Vagadia et al. (2015) state that soya “contains a variety of bioactive anti-nutritional compounds including protease trypsin inhibitors, phytic acid, and isoflavones that exhibit undesirable physiological effects and impede their nutritional quality. Inactivation of these trypsin inhibitors, along with deleterious enzymes, microbes, bioactive components and increasing the protein quality by improving its texture, colour, flavour, functionality and digestibility are the most important factors to be considered in the crucial stage in the manufacturing of soy products.” Are there reasons to be concerned and what can we learn about its history and possible applications in the meat industry?
Historically Valued Plant
Before we break down the concerns raised by Vagadia et al. (2015), it is instructive to know that soya has been consumed in many countries since before recorded history. A rich tradition developed around its use in medicine from antiquity. Duke (1991) showed that a search of his “Medicinal Plants of the World” database (Sept. 1981) indicated that soybeans are or have been used medicinally in China to treat the following symptoms/diseases or for the following medicinal properties (listed alphabetically; Most information from: Li Shih-Chen. 1973. Chinese Medicinal Herbs. San Francisco: Georgetown Press):
Uses in other parts of the world include cancer, and cyanogenetic, shampoo (USA), diabetes (Turkey), soap (Asia), stomach problems (India).
Not only was it recognized as a superfood in many parts of the world, but it was celebrated for its medicinal value. Looking at the factors of concern raised by many, we begin by looking at the most well-known concern factor of its role as a trypsin inhibitor.
The German physiologist Wilhelm Kühne (1837-1900) discovered trypsin in 1876. It is an enzyme that cleaves peptide bonds in proteins (serine protease) and is therefore essential in digestion. It is found in the digestive system of many vertebrates, where it hydrolyzes proteins. (Kühne, 1877) Trypsin is formed in the small intestine when its proenzyme form, the trypsinogen, produced by the pancreas, is activated. (Engelking, 2015) A trypsin inhibitor (TI) is then something (a protein) that reduces the biological activity of trypsin and as such have a negative effect on nutrition by impairing the digestion of food.
The concern about soya’s trypsin inhibitors is of no real concern to us. It turns out that trypsin in humans is more resistant to inhibition than is the trypsin of other mammalian species. “The effect on human trypsin of soybean trypsin inhibition in soy protein does not appear to be a potential hazard to man. Therefore, the elimination of STI does not seem to be necessary for humans.” (Flavin DF, 1982)
“In animal diets, however, pancreatic toxicity must be considered whenever soybean protein is utilized. Soybeans should be treated to increase their nutritional benefits and decrease any animal health risks. This will ensure healthy control subjects in laboratory situations and avoid misinterpretation of pathologic data.
The treatment suggested is heat since heat will destroy most of the soybean trypsin inhibitors. Additional supplementation is required following heat treatment for amino acids such as methionine, valine, and threonine; for choline; and for the minerals zinc and calcium. Excessive heat must be avoided since it will decrease the nutritional value of soybean protein and increase lysinoalanine, a nephrotoxic substance.
Finally, the use of STI as a promotor in the study of potential pancreatic carcinogens may prove beneficial for cancer research and might be considered in the future.” (Flavin DF, 1982)
Phytic acid also is suspect due to its inhibitory effect related to nutrition. Anderson (2018) states “It is a unique natural substance found in plant seeds. It has received considerable attention due to its effects on mineral absorption. Phytic acid impairs the absorption of iron, zinc, and calcium and may promote mineral deficiencies” (Arnarson, 2018)
As is the case with the trypsin inhibition, the story is a bit more complicated than that because phytic acid also has a number of health benefits.
Anderson writes that “phytic acid, or phytate, is found in plant seeds. It serves as the main storage form of phosphorus in the seeds. When seeds sprout, phytate is degraded and the phosphorus released to be used by the young plant. Phytic acid is also known as inositol hexaphosphate, or IP6. It’s often used commercially as a preservative due to its antioxidant properties.
Phytic acid is only found in plant-derived foods. All edible seeds, grains, legumes and nuts contain it in varying quantities, and small amounts are also found in roots and tubers. The following table shows the amount contained in a few high-phytate foods, as a percentage of dry weight:
As you can see, the phytic acid content is highly variable. For example, the amount contained in almonds can vary up to 20-fold.
Phytic acid impairs absorption of iron and zinc, and to a lesser extent calcium. This applies to a single meal, not overall nutrient absorption throughout the day. In other words, phytic acid reduces mineral absorption during the meal but doesn’t have any effect on subsequent meals. For example, snacking on nuts between meals could reduce the amount of iron, zinc and calcium you absorb from these nuts but not from the meal you eat a few hours later.
However, when you eat high-phytate foods with most of your meals, mineral deficiencies may develop over time. This is rarely a concern for those who follow well-balanced diets but may be a significant problem during periods of malnutrition and in developing countries where the main food source is grains or legumes.
Avoiding all foods that contain phytic acid is a bad idea because many of them are healthy and nutritious. Also, in many developing countries, food is scarce and people need to rely on grains and legumes as their main dietary staples.
Phytic acid is a good example of a nutrient that is both good and bad, depending on the circumstances. For most people, it’s a healthy plant compound. Not only is phytic acid an antioxidant, but it may also be protective against kidney stones and cancer. Scientists have even suggested that phytic acid may be part of the reason why whole grains have been linked with a reduced risk of colon cancer.
Phytic acid is not a health concern for those who follow a balanced diet. However, those at risk of an iron or zinc deficiency should diversify their diets and not include high-phytate foods in all meals. This may be especially important for those with an iron deficiency, as well as vegetarians and vegans.
There are two types of iron in foods: heme iron and non-heme iron. Heme-iron is found in animal foods, such as meat, whereas non-heme iron comes from plants.
Non-heme iron from plant-derived foods is poorly absorbed, while the absorption of heme-iron is efficient. Non-heme iron is also highly affected by phytic acid, whereas heme-iron is not. In addition, zinc is well absorbed from meat, even in the presence of phytic acid.
Therefore, mineral deficiencies caused by phytic acid are rarely a concern among meat-eaters. However, phytic acid can be a significant problem when diets are largely composed of high-phytate foods while at the same time low in meat or other animal-derived products. This is of particular concern in many developing nations where whole grain cereals and legumes are a large part of the diet.” (Arnarson, 2018)
Isoflavones are a class of phytoestrogens — plant-derived compounds with estrogenic activity. Soybeans and soy products are the richest sources of isoflavones in the human diet. (oregonstate.edu)
“Since many breast cancers need estrogen to grow, it would stand to reason that soy could increase breast cancer risk. However, this isn’t the case in most studies.
In a review of 35 studies on soy isoflavone intake and breast cancer incidence, higher soy intake reduced breast cancer risk in both pre- and postmenopausal Asian women. For women in Western countries, one study showed soy intake had no effect on the risk of developing breast cancer.
This difference may be due to the different types of soy eaten in the Asian compared to the Western diet. Soy is typically consumed whole or fermented in Asian diets, whereas in Western countries, soy is mostly processed or in supplement form.
In an animal study, rats fed fermented soy milk were 20% less likely to develop breast cancer than rats not receiving this type of food. Rats fed soy isoflavones were 10–13% less likely to develop breast cancer. Therefore, fermented soy may have a more protective effect against breast cancer compared to soy supplements. Additionally, soy has been linked to a longer lifespan after breast cancer diagnosis.
In a review of five long-term studies, women who ate soy after diagnosis were 21% less likely to have a recurrence of cancer and 15% less likely to die than women who avoided soy.” (Groves, 2018)
From the above notes, it may appear that it is perfectly safe for humans to consume raw soya. There is however one very good reason to cook soya well before it is consumed.
“Soybeans contain lectins, glycoproteins that bind to carbohydrates in cells. This can damage the cells or lead to cell death in the gastrointestinal tract. Lectins may bind to the intestinal walls, damaging the cells and affecting nutrient absorption as well as causing short-term gastrointestinal side effects. Unlike most proteins, lectins aren’t broken down by enzymes in the intestine, so the body can’t use them. Lectins can affect the normal balance of bacteria in the intestine and the immune system in the digestive tract.” (Perkins, 2018)
Dr. Mark Messina discussed the issue with Lectin in soya in a brilliant article entitled “Is Soybean Lectin an Issue?” He writes, “Given all the attention they’re receiving, you might think these proteins are newly discovered, perhaps because of a sudden advance in technology. Given all the concerns being raised about them, you might be thinking of avoiding foods that contain them. If you do, you can pretty much say goodbye to a long list of healthy foods such as legumes (including soy and peanuts), eggplant, peppers, potatoes, tomatoes, and avocados. Despite the hoopla, studies show there is little reason for concern.
Lectins are anything but new to the scientific community. They are a class of protein that occurs widely in nature and have been known to exist in plants for more than a century. Much of the lectin research has focused on legume lectins but these carbohydrate-binding proteins are widely distributed throughout the plant kingdom. The lectin in soybeans was discovered in the 1950s.
In plants, lectins appear to function as nitrogen storage compounds, but also have a defensive role, protecting the plant against pests and predators. They are capable of specific recognition of and binding to carbohydrate ligands. The term lectin (legere = Latin verb for to select) was coined by Boyd circa 1950 to emphasize the ability of some hemagglutinins (lectins) to discriminate blood cells within the ABO blood group system.5-The term lectin is preferred over that of hemagglutinin and is broadly employed to denote “all plant proteins possessing at least one non-catalytic domain, which binds reversibly to a specific mono- or oligosaccharide.”
Orally ingested plant lectins remaining at least partially undigested in the gut may bind to a wide variety of cell membranes and glycoconjugates of the intestinal and colonic mucosa leading to various deleterious effects on the mucosa itself as well as on the intestinal bacterial flora and other inner organs. The severity of these adverse effects may depend upon the gut region to which the lectin binds. Several cases of lectin poisoning due to the consumption of raw or improperly processed kidney beans have been reported.
The lectin content of soybeans varies considerably among varieties, as much as fivefold. However, from a nutritional perspective, it is the amount in properly processed soyfoods that is most relevant. Although there has been a lot of debate about whether even active soybean lectin is harmful, a true pioneer in this field, Irvin E. Liener, concluded that soybean lectin isn’t a concern because it is readily inactivated by pepsin and the hydrolases of the brush border membrane of the intestine. But, others think soybean lectin does survive passage through the small intestine.
Not surprisingly, autoclaving legumes including soybeans completely inactivates lectins. However, foods aren’t typically autoclaved. The most practical, effective, and commonly used method to abolish lectin activity is aqueous heat treatment. Under conditions where the seeds are first fully soaked in water and then heated in water at or close to 100°C, the lectin activity in fully hydrated soybeans, kidney beans, faba beans, and lupin seeds is completely eliminated. Thompson et al. noted that cooking beans to the point where they might be considered edible are more than sufficient to destroy virtually all of the hemagglutinating activity of lectins. More recently, Shi and colleagues23 found that soaking and cooking soybeans destroyed more than 99.6% of the lectin content, which agrees with earlier work by Paredes-Lopez and Harry.
Finally, evidence from clinical trials in no way suggests that the possible residual lectin content of soyfoods is a cause for concern. Adverse effects typically associated with lectin toxicity don’t show up in the hundreds of clinical trials involving a range of soy products that have been published. Not surprisingly, the U.S. Food and Drug Administration recently concluded that soy protein is safe.” (Messina, 2018)
Saponins in Soybeans
Saponins in soya are responsible for the bitter taste, foam-forming, and activities that rupture or destroy red blood cells. Its presence in soya is probably an evolutionary development to protect it against, for example, Callosobruchus chinensis L., a common species of beetle. Its protecting properties can be seen for example by the fact that [certain strains of] the first instar larvae, after burrowing beneath the seed coat, subsequently die without moulting. (Applebaum, 1965)
There are five known soya saponins: Soya sapogenols A, B, C, D, and E. Saponins cannot be inactivated by cooking because cooking doesn’t break down this toxin like it does lectins.” (Perkins, 2018) “Triterpenoid saponins in the mature soybean are divided into two groups; group A soy saponins have undesirable astringent taste, and group B soy saponins have health-promoting properties. Group A soy saponins are found only in soybean hypocotyls, while group B soy saponins are widely distributed in legume seeds in both hypocotyls (germ) and cotyledons. Saponin concentrations in soybean seed are ranged from 0.5 to 6.5%.” (Hassan, 2013)
Bondi and Birk (1966) investigated soybean saponins as related to the processing of petroleum etherextracted meal for feed and to the preparation of soy foods. They found that “soybean saponins are harmless when ingested by chicks, rats and mice even in a roughly threefold concentration of that in a 50% soybean meal supplemented diet.” They are decomposed by the caecal microflora of these 3 species. Their non-specific inhibition of certain digestive enzymes and cholinesterase is counteracted by proteins which are present in any natural environment of these saponins. The haemolytic activity of soybean saponins on red blood cells is fully inhibited by plasma and its constituents –
which naturally accompany red cells in blood. Soybean saponins and sapogenins are not absorbed into the blood-stream (Note: Or perhaps not observed in the bloodstream). It may, therefore, be concluded that haemolysis – one of the most significant in vitro [in glass/test tubes] properties of soybean saponins and others–bears no ‘obligation’ for
detrimental activity in vivo [in living organisms].” (Bondi, et al, 1966)
Birk, et al, 1980, found that “saponins are glycosides that occur in a wide variety of plants. They are generally characterized by their bitter taste, foaming in aqueous solutions, and their ability to hemolyze [break down] red blood cells. The saponins are
highly toxic to cold-blooded animals, their toxicity being related to their activity in lowering surface tension. They are commonly isolated by extraction of the plant material with hot water or ethanol.” (Birk, 1980) Leaching the saponins out of the soybeans, removing the bitter taste. (Perkins, 2018)
Applications and History
Reviewing the history of the development of soya industry in Israel, brought up some interesting perspective on its application in food.
“Hayes Ashdod was one of Israel’s first company to make foods from soybeans and Israel’s first manufacturer of modern soy protein products. In 1963 the company launched its first product, a soy protein concentrate named Haypro. This product was also the first commercial soy protein concentrate manufactured outside the United States. The main applications for Haypro were as a meat extender.” (Chajuss, 2005)
“In 1966 Hayes Ashdod Ltd. introduced texturized soya protein concentrates under the brand names Hayprotex and Contex. Hayprotex was designed for use mainly as a minced
meat extender, while Contex was designed mainly for vegetarian analogs.” (Chajuss, 2005)
“Concerning early textured soy protein concentrates: Hayes Ashdod introduced Hayprotex and Contex in 1966, and a company we are well familiar with for making nitrite curing of meat commercially available around the world through their legendary Prague Powder, the Griffith Laboratories from Chicago introduced GL-219 and GL-9921 in 1974, and Central Soya introduced Response in 1975.” (Chajuss, 2005)
“In 1969 Hayes started to produce Primepro, a more functional and soluble soy protein concentrate, by further treatment of the aqueous alcohol extracted soy protein concentrate (Haypro), for use as substitutes for soy protein isolates and for caseinates in various food systems, especially in the meat processing industries.” (Chajuss, 2005)
Soya is a tremendous food and protein source. The health concerns are addressed at the manufacturing stage. Application of isolates, concentrates and TVP are multiple. Even today, after being available on the market for so many years, all its various applications in foods have not been exhausted. We are limited only by our imagination and interesting work remains to integrate its use into modern meat processing plants.
Applebaum, S.W.; Gestetner, B.; Birk, Y. 1965. Physiological aspects of host specificity in the Bruchidae–IV. Developmental incompatibility of soybeans for Callosobruchus. J. of Insect Physiology 11(5):611-16. May.
Birk, Yehudith; Peri, Irena. 1980. Saponins. In: I.E. Liener, ed. 1980. Toxic Constituents of Plant Foodstuffs. 2nd ed. New York: Academic Press. xiv + 502 p. See p. 161-182. Chap. 6.
Bondi, A.; Birk, A. 1966. Investigation of soybean saponins as related to the processing of petroleum ether-extracted meal for feed and to the preparation of soy foods, to provide information basic to improving the nutritional value of soybean protein products. Rehovot, Israel: Hebrew University. 80 + xvii p. USDA P.L. 480. Project no. UR-A10-(40)-18. Grant no. FG-IS-112. Report period 1 March 1961 to 28 Feb. 1966. Undated. 28 cm.
Chajuss, D.. 2005. Brief biography and history of his work with soy in the USA and Israel. Part II (Interview). SoyaScan Notes. Feb. 19. Followed by numerous e-mails. Conducted by William Shurtleff of Soyfoods Center.
Duke, J. A. 1991. Research on biologically active phytochemicals in soybeans (Interview). SoyaScan Notes. Oct. Conducted by William Shurtleff of Soyfoods Center.
Vagadia, B. H., Vanga, S. K., Raghavan, V. 2015. Inactivation methods of soybean trypsin inhibitor – A review. Received 14 December 2015, Revised 21 January 2017, Accepted 19 February 2017, Available online 27 February 2017. Elsevier. Trends in Food Science & Technology, Volume 64, June 2017, Pages 115-125
We have progressed in our study of the historical development of the concept of using Nitrogen to determine meat content to the Proximate analysis, and its accompanying use of the Kjeldahl method, the Jones factors and a review of the nutritional importance of the Proximate system. Our study leads us to unexpected places as we are challenged in our views on managing a complex operation like a large food factory.
The history of the development of food analysis goes back to the people we met in our introductory articles in the persons of Baussingault, and Liebig. To the list, we should probably add Sir Humphrey Davey, but Davey held a fundamentally different view of nutrition compared to Liebig and Baussingault. Where these two men held the basis for plant nutrition to be mineral, Davey was in the camp of Albrecht Daniel von Thaer (1752-1828) on the subjected who believed humus to be the foundational principle of plant nutrition. “According to this theory, humus is the main source of plant nutrients, next to the previously recognized role of water, obviously. In Thaer’s opinion, minerals played only a supporting role in providing plants with humic compounds. Therefore, the whole soil fertility depends only on the amount of humus present in it. He presented his views in his work “The Principles of Agriculture”.” (Antonkiewicz and Łabetowicz, 2016)
“The humus theory for plant nutrition was the dominant concept explaining the essence of plant nutrition for tens of years. Von Liebig was the first to explain, through his experimental works, the basics of the problem of mineral plant nutrition. In 1841, a publication entitled “Die Organische Chemie in ihrer Anwendung auf Agrikultur und Physiologie” – “Organic Chemistry in Its Applications to Agriculture and Physiology” was released, with a new theory of mineral plant nutrition. This book opens a new chapter in the development of the science of plant nutrition. It attracted great interest not only in scientific world but also among a lot of farmers. Liebig wrote that not humus but mineral salts (are taken up with water by roots from soil) and carbon dioxide assimilated from air in the photosynthesis process are the direct food for plants. For stable plant yields, soil should be supplied with mineral fertilizers in order to replenish the deficiency of nutrients caused by their removal from the field along with plant yield. Liebig formulated his theory about mineral plant nutrition based on other scientists’ studies, and also through deduction from a chemical analysis of plants. As a chemist and analyst, he conducted many studies on the chemical composition of plants. He determined that plants release carbon, hydrogen, oxygen and nitrogen (which are present in them) during combustion, and composition of the generated ash always includes phosphorus, sulfur, calcium, potassium, magnesium, silicon, and many times sodium.” (Antonkiewicz and Łabetowicz, 2016)
In the end, it was the scientific rigour of Liebig that won the day. Not just his new techniques opened up new discoveries, but also the question of whether science and practice presented a duality. These two concepts were juxtaposed in the mind of the landowners who saw the views of Liebig and Albrecht Daniel von Thaer as much more than a debate about the essence of plant nutrition. Liebig’s word was scientific and based in a laboratory. Of course, it had to have practical application, but he wrestled with solving fundamental questions first before he moved on to the practical and in many instances, as we know from our own experiences, even the best scientific work doesn’t always work in practice at the first attempt. Such is the nature of the beast.
Von Thaer, on the other hand, was a consummate pragmatist and by all accounts, a skilled manager. I am impressed by the reported neatness of the workshops on the estates that he was in charge of. Reports have it that they were open for inspection by the public and everything had its place. Thaer’s work, “Principles of Agriculture” contain the result of his experience through a series of years. We can feel his passion and approach in his work. It embraces the theory of the soil, the clearing of land, ploughing, manuring, and irrigation, hedges and fences, management of meadow and pasture lands; the cultivation of wheat, rye, corn, oats, barley, buckwheat, hops, tobacco, clover, and all the varieties of grasses; the economy of kine stock, breeding and feeding; the management of the dairy, and the use of manures, and the various systems of cultivation, keeping journals and farm records. In brief, it is a complete cyclopaedia or circle of practical agriculture. (Homans, 1857)
These issues that we don’t necessarily see as opposing views today would take on a life of its own in Germany which impacted (determined?) the course of history related to the nutritional sciences and the evaluation of foods.
As Liebig’s approach of rigorous science and experimentation started to dominate, tools were being developed on which more discoveries were predicated. Better techniques were developed, gradually, to separate the food fragments which played a role in nutrition including protein, fat, and fibre. The Liebig/ Dumas method for example, for determining the Nitrogen content in food was developed in 1830 and 1840. The famous Kjeldahl method was published in 1883 and much later the use of the 6.25 conversion number of N to protein would become the more complete Jones numbers. At the dawn of the 20th century, food chemistry was firmly established. (Dryden, 2008) Along with improved techniques and tools, the philosophical wars raged on.
The Proximate Analysis
The German Agriculture Research Stations was a driving force in the development of German farming from the mid-1800s and a model for similar developments around the world. Wilhelm Crusius has it that the first German Agricultural Research Station was created on 28 September 1850 during a banquet honouring Leipzig’s new marble statue of Albrecht Daniel von Thaer. He recalls that several agricultural leaders from the kingdom of Saxony agreed to terms that saw the Möckern estate near Leipzig transformed into an institution to investigate the application of scientific knowledge to agriculture. The Möckern facility is widely believed to be the words first state-supported agriculture research station. It was believed that the Möckern facility represented a fulfilment of Thaer’s vision. He propagated a system of “rational” agriculture. Landowners loved him as they looked for ways to increase their yields through comparative investigations, but was sceptical of what we call research. (Finlay, 1988)
It is generally believed to be Liebig who founded the agriculture research stations, through his 1840 work Chemistry and its application to Agriculture and Physiology. Many suggested that it was the excitement created by this publication around the world, that Germanys research stations were founded upon. It is believed by many that the agricultural research station became a haven for the agricultural chemists. The line of thinking then continues that the American Agricultural stations were created based on the German model in the 1870’s and 80’s. Even the notion of research is also linked to Liebig through his famous research laboratory in Giesen. (Finlay, 1988)
A study of the Möckern facility challenge these notions. Fundamental science and agriculture chemistry were not, in fact, initial driving forces behind this first agriculture station. The Saxon officials had praise for Liebig’s recognition of the importance of chemical compounds in plants and animal growth but scorned his insistence on laboratory research. Liebig created plant manure in his laboratory. It was practically insoluble. A white chemical crust formed over fields in practical demonstrations and his invention was a disaster. Many believe that the creation of the agriculture stations would provide an opportunity to verify such work. They saw a division between science and practice and the stations would be a place to unite these two polar opposites. In the early days of the Möckern facility, scientists and what was called “practitioners” had equal authority. As in America, in Germany, the scientists did not win control over these stations for some time and not after a long and hard battle. (Finlay, 1988)
The German Agriculture Experiment stations became the model for similar stations set up in America. Wilbur Atwater of Connecticut had great admiration for the Möckern station. He got involved in work at another station, the one at Weende. Here they were involved in calorimeter research in the 1860s and Atwater expanded on the research. (Marcus, 2015)
Weende Experiment Station
The physiological chemistry work of Liebig had only an indirect application in agriculture. Wilhelm Henneberg was one of his students who applied his theories and methods directly in agriculture research. This would be one example of the triumph of science and laboratory research and fundamental to our understanding of the current methods for determining meat content. Scientists at these research stations directed the priority of work away from the achievement of immediate practical goals and towards the examination of basic scientific questions. Henneberg became the director at the Agriculture Experiment Station at Weende near Göttingen in 1857. He made a huge contribution to this shift and introduced a program using livestock as experimental organisms, incorporating the methods and instruments that he was introduced to in Munich. Precision and quantification were very important to him. He used instruments like the Petterkoffer respiration apparatus. (Phillips and Kingsland, 2015)
He stressed the importance of controlling environmental variables in laboratory settings and focused on fundamental questions in animal metabolism. His assistant was Frederich Stohmann who helped with the findings of his experiments. They directed the findings at farmers and physiologists, but in reality, made no effort to practically apply the results of their work. (Phillips and Kingsland, 2015)
Henneberg challenged the view of Thaer who emphasised close interaction of science and practice and the integration of plant and animal agriculture. Agriculture sciences rose to great prominence in Germany during this time and animal nutrition was one of its most successful branches. (Phillips and Kingsland, 2015)
Henneberg and Stohmann (1860, 1864) developed a top-level, very broad, classification of food components for routine analysis which they devised for animal feed. It is a “partitioning of compounds in feed into six categories based on the chemical properties of the compounds. This analysis was an attempt to duplicate animal digestion. (Artemia)
After extracting the fat, the sample is subjected to an acid digestion, simulating the acid present in the stomach, followed by an alkaline digestion, simulating the alkaline environment in the small intestine. The crude fibre remaining after digestion is the portion of the sample assumed not digestible by monogastric animals. In the proximate analysis of feedstuffs, Kjeldahl nitrogen, ether extract, crude fibre, and ash are determined chemically. The determination of nitrogen allows the calculation of the protein content of the sample. It is important to remember that proximate analysis is not a nutrient analysis, rather it is a partitioning of both nutrients and non-nutrients into categories based on common chemical properties.” (Artemia)
“At that time the nutritionally important components of protein had not been recognized, all neutral fats were considered to be nonspecific sources of energy, and vitamins were unknown. However, the multiplicity of the carbohydrates and the practical difficulties of their separate chemical determination were clearly recognized. These workers believed that for nutritional description the carbohydrates could be grouped into (1) the starches and the sugars, and (2) a coarse fibrous fraction. The latter they isolated as an insoluble residue after boiling the food sample first with dilute acid and then with dilute alkali. These procedures were intended to simulate the acidic gastric digestion and the subsequent alkaline intestinal digestion of ingested food. The insoluble residue they called crude fibre. With analytical figures for ether extract, ash, nitrogen, and crude fibre of a moisture-free food sample, they needed only to convert the value for nitrogen to its equivalent in terms of protein (i.e., N x 6.25), add to this the other three group values, and subtract the total from the original weight of dry sample, thus by difference to arrive at an estimate of the “soluble carbohydrates.” This fraction they called nitrogen-free extract (NFE).” (Loyed, et al. 1960)
“The majority of foods in human diets, as well as those in the diets of some laboratory animals used in nutrition studies, are so low in crude fibre that this fraction can often be disregarded, and the custom has gradually become general, especially in human nutrition, to omit the crude fibre determination. When this is done it is the total carbohydrate that is estimated “by difference.” (Loyed, et al. 1960)
“Probably because the chief components of nitrogen-free extract (NFE) are sugars and starches, we are prone to forget that this fraction includes all the nonfibrous, ether–insoluble, water-soluble organic materials of the food (or other material analyzed). Thus all water-soluble vitamins must be included in this fraction. Quantitatively, the vitamins are an insignificant part of the NFE, but in any broad charting of the makeup of foods in terms of the Weende partition these vitamins are part of the NFE in the same way that the fat-soluble vitamins are part of ether extract.” (Loyed, et al. 1960)
“Being determined by difference, the figure for NFE is also subject to an appreciable but variable error that may be as large as the algebraic sum of any analytical and/or sampling errors of each of those fractions determined by direct analysis.
Variability of average
Weende analysis values
It is appropriate at this point to comment on the errors to be expected in numerical values obtained from the several parts of the Weende analysis. These arise from several sources. Errors in the chemical manipulations-that are, analysts’ errors are usually negligible. Sampling errors, however, are often large because foods and the residues of animal digestion are not usually homogeneous. In addition, different lots of foods called by the same name are seldom identical in “proximate” makeup. Consequently, average composition figures found in tables of food composition are not necessarily applicable to a particular lot of a foodstuff. Nevertheless, it is often more feasible to estimate the protein, or the fat, or the carbohydrate, of some particular lot of a foodstuff by referring to tables of average composition than to obtain specific values by analysis. When average values are used in this way it should be remembered that the composition figures given for natural foods may be subject to coefficients of variation such as those listed in the table below.” (Loyed, et al. 1960)
“For example, if the average crude protein content of cornmeal is given in a table as 10%, it is probable that two samples out of three purchased at random would on analysis give values between 9.2 [10 minus 10 (8%)] and 10.8 [10 plus 10(8%)] percent protein (see figure above). Similarly, cornmeal may average 72% NFE, and hence two samples out of three might be expected to give values between 69.8% and 74.2% (that is, 72 ± 3%).” (Loyed, et al. 1960)
This current application of this system of analysis can be summarised as follows:
The moisture content is determined as the loss in weight that results from drying a known weight of food to constant weight at 100 degrees C. This method is satisfactory for most foods, but with a few, such as silage, significant losses of volatile material may take place.
The ash content is determined by ignition of a known weight of the food at 550°C until all carbon has been removed. The residue is the ash and is taken to represent the inorganic constituents of the food. The ash may, however, contain material of organic origin such as sulphur and phosphorus from proteins, and some loss of volatile material in the form of sodium, chloride, potassium, phosphorus, and sulphur will take place during ignition. The ash content is thus not truly representative of the inorganic material in the food either qualitatively or quantitatively. There is incomplete recovery of individual minerals. It is one of the aspects of the proximate analysis, less used in modern food analysis. (hmhub.me) “Ash is a mixture of food minerals. The food Organic Matter (OM) content is (OM = DM – ash) is frequently used as a way of correcting data for mineral contamination, as will happen when measurements are made with grazing animals.” (Dryden, 2008)
The crude protein (CP) content is calculated from the nitrogen content of the food, determined by a modification of a technique originally devised by Kjeldahl over 100 years ago. In this method, the food is digested with sulphuric acid, which converts to ammonia all nitrogen present except that in the form of nitrate and nitrite. This ammonia is liberated by adding sodium hydroxide to the digest, distilled off and collected in standard acid, the quantity so collected being determined by titration or by an automated colourimetric method. It is assumed that the nitrogen is derived from protein containing 16 percent nitrogen, and by multiplying the nitrogen figure by 6.25 (i.e. 100/16) an approximate protein value is obtained. This is not ‘true protein’ since the method determines nitrogen from sources other than protein, such as free amino acids, amines and nucleic acids, and the fraction is therefore designated crude protein. (hmhub.me)
The Dumas method in which a sample is burnt and the N gas released is measured, was developed before the Kjeldahl method but has become popular only following the development of automated methods of carrying out the analysis. The method recovers all the sample N and so may give slightly higher values than the Kjeldahl method, depending on the sample analysed.” (Dryden, 2008)
The ether extract (EE) fraction is determined by subjecting the food to a continuous extraction with petroleum ether for a defined period. The residue, after evaporation of the solvent, is the ether extract. As well as lipids it contains organic acids, alcohol, pigments, fat-soluble vitamins, waxes, as well as fats. (hmhub.me) It is used to isolate lipids for more detailed fractionation into fatty acids and waxes. The EE is, nevertheless, still reported as a measure for total lipid. In the current official method, the extraction with ether is preceded by hydrolysis of the sample with sulphuric acid and the resultant residue is the acid ether extract. (Dryden, 2008)
crude fibre, and
Einhof extracted the fibrous part of food in 1805. His concept of fibre is very distant from our present-day understanding. To him, it was what was obtained after rubbing and washing the food to obtain the residue that is “resistant.” He may have thought that it was not nutritious. Boussingault and Davy specifically stated that it is not since it could not be digested. They had no experimental proof of this. (Dryden, 2008) Henneberg and Stohmann developed a method for analyzing crude fiber in 1859. The carbohydrate of the food is contained in two fractions, the crude fibre (CF) and the nitrogen-free extractives (NFE). The former is determined by subjecting the residual food from ether extraction to successive treatments with boiling acid and alkali of defined concentration; the organic residue is the crude fibre. (hmhub.me)
When the sum of the amounts of moisture, ash, crude protein, ether extract and crude fibre (expressed in g/kg) is subtracted from 1000, the difference is designated the nitrogen-free extractives. The crude fibre fraction contains cellulose, lignin, and hemicelluloses, but not necessarily the whole amounts of these that are present in the food: a variable proportion, depending upon the species and stage of growth of the plant material, is contained in the nitrogen-free extractives. Nitrogen Fee Extracts (NFE) was originally assumed to be mainly soluble carbohydrate and so was expected to be highly digestible. The nitrogen-free extractives fraction is a heterogeneous mixture of all those components not determined in the other fractions. It includes sugars, fructans, starch, pectins, organic acids, and pigments, in addition to those components mentioned above. (hmhub.me)
“Unfortunately, the reagents used to measure crude fibre (CF), may remove up to 60% of the cellulose, about 80% of the hemicellulose and a highly variable (10 – 95%) proportion of the lignin.The NFE contains some of the plant cell wall material an can be less digestible than CF. Besides this, NFE contains all those chemical entities which are not measured by the other methods. NFE is not now used in food analysis.” (Dryden, 2008)
Schematically, it can be represented as follows: (chart by (Dryden, 2008))
This system had a long-lasting effect on our approach to food analysis. We still use Dry Matter as the basis for expressing analytical data in calculating food intake of formulating diets. (Dryden, 2008)
“The chemistry of nitrogen is complex due to the fact that nitrogen assumes several oxidation states (Sawyer et al., 2003). Nitrogen is one of the most important elements for plant nutrition. The compounds of nitrogen are of great worth in water resources, in the atmosphere, and in the life process of all plants and animals. Four forms of dissolved nitrogen are of greater interest: organic, ammonia, nitrite, and nitrate, ordered in an increasing state of oxidation. All these forms of nitrogen, as well as nitrogen gas (N2), are mutually convertible, being components of the biological nitrogen cycle (Pehlivanoglou-Mantas and Sedlak, 2006; Worsfold et al., 2008). It is very important to ascertain the contribution (fractions) of different nitrogen species to the total nitrogen content (Prusisz et al., 2007).
Testing for N
The modern version of the proximate analysis uses mostly the Kjeldahl method of testing for N. Few other companies in history had such a dramatic effect on chemistry in general and food chemistry in particular as the Danish beer producer, Carlsberg. S.P.L. Sørensen was Director of the Carlsberg Laboratory’s Department of Chemistry from 1901 to 1938. In 1909, he developed the pH scale – a method for specifying the level of acidity or alkalinity of a solution on a scale from 0-14 and demonstrated the significance of pH for biochemical reactions, including those involved in brewing. With the invention of the pH scale, Carlsberg could ensure high quality of every beer. The applications of the pH scale have since been countless throughout all fields. (carlsberggroup.com)
It is remarkable that more than 20 years before the pH scale was invented, his predecessor from the same institution invented the definitive measurement for N in protein. Here is the story, told by Sáez-Plaza, et al. in their Overview of the Kjeldahl Method of Nitrogen Determination, Part I and Part II.
“The Danish chemist Johan Gustav Christoffer Thorsager Kjeldahl (1849–1900), Head of Chemistry Department of the Carlsberg Foundation Laboratory of the Danish Brewing Carlsberg Company, introduced a method known later under the eponym the Kjeldahl method that basically is still in use. It was first made public at a meeting of the Danish Chemical Society (Kemisk Forening) held on March 7, 1883 (Burns, 1984; Johannsen, 1900; McKenzie, 1994; Oesper, 1934; Ottensen, 1983, Veibel, 1949). Within the same year, the method was published in the German journal Zeitschrift f¨ur Analytische Chemie (Kjeldahl, 1883a), and written in French and Danish languages in communications from the Carlsberg Laboratory (Holter and Møller, 1976; Kjeldahl, 1883b, 1883c; Ottesen, 1983).” (Sáez-Plaza, et al, 2013)
“Because of the respect that the founder of the laboratory, the Danish brewer J. C. Jacobsen, had for Pasteur and his work for the French wine industry (Burns, 1984), extensive French summaries of the Carlsberg papers were also published. As an extended summary of the Kjeldahl paper appeared in Chemical News in August (Kjeldahl, 1883d), the method was quickly taken up (Sella, 2008). The Analyst first gave details of the method in 1885 “for the benefit of those who may have missed the original paper” (Burns, 1984; Editor of The Analyst, 1885, p. 127), although the method had been briefly mentioned by Blyth (1884), who gave Kjeldahl’s name incorrectly as Vijeldahl. A surprisingly short period went by between the publication of the Kjeldahl method and the appearance of publications affecting further improvements (Dyer, 1895; Hepburn, 1908; Kebler, 1891; Vickery, 1946a), both in Europe and the U.S., due to the tremendous impact that the Kjeldahl work had on others, especially in Germany (McKenzie, 1994).
Most of the earlier contributions were discussed by Fresenius in the Zeitschrift, often to a length of several pages (Vickery, 1946a). Throughout the history of analytical chemistry, none of the methods has been as widely adopted, in so short a time, as the “Kjeldahl Method” for the estimation of nitrogen, as stated by Kebler (1891) at the beginning of an annotation in which he compiled references on the estimation of nitrogen by the Kjeldahl method (some 60) and by all other methods (about 200).” (Sáez-Plaza, et al, 2013)
“The Kjeldahl method was originally designed for the brewing industry as an aid in following protein changes in grain during germination and fermentation (Bradstreet, 1940; Kjeldahl, 1883b); the lower the amount of protein in the mush, the higher the volume of beer produced. It was Berzelius who suggested the use of the word “protein” in 1838 in a letter to Mulder because it was derived from the Greek word meaning “to be in the first place” (Zelitch, 1985). The Kjeldahl protein content is strictly dependent on total organic nitrogen content (Wong et al., n.d.); i.e., protein structure will not interfere
with the accuracy of protein determination.”
As we have mentioned earlier in this article, a drawback of the Kjeldahl method is that it lacks the “analytical selectivity because it does not distinguish protein-based nitrogen from nonprotein nitrogen. Adulteration incidents (e.g., adulteration of protein-based foods with melanine and related nonprotein compounds) exploiting this analytical vulnerability have been recently detected (Breidbach et al., 2010; Levinson and Gilbride, 2011; Moore et al., 2010; Tyan et al., 2009) and are new examples of a problem that dates back to before the Kjeldahl method was introduced (M¨oller, 2010a).” (Sáez-Plaza, et al, 2013)
“The presence of non-protein nitrogen (NPN) compounds in foods (aminoacids, ammonia, urea, trimethylamine oxide) overestimates their true protein content (M¨oller, 2010a; van Camp and Huyghebaert, 1996; Yuan et al., 2010) as derived from the current nitrogen determination methods. Separation of NPN from true protein nitrogen may be carried out by adding a protein precipitating agent such as trichloroacetic acid or perchloric acid (Rowland, 1938a, 1938b). The process conditions applied during protein precipitation, however, affect the composition and the amount of NPN, so it is mandatory to specify the type and concentration of precipitating agents used in each case. Alternative techniques such as dialysis and gel filtration are probably more accurate in removing the NPN fraction (van Camp and Huyghebaert, 1996), but they remain unacceptable for routine analysis. Reviews of NPN determination methods in cow milk, and on aspects concerning the composition of NPN fraction, are given by Wolfschoon-Pombo and Klostermeyer (1981, 1982). The Kjeldahl method measures what is termed total protein (American Jersey Cattle Association, n.d.). The alternative use of true protein (total nitrogen minus the NPN) has been under debate for some years (Grappin, 1992; Harding, 1992; Rouch et al., 2007; Salo-V¨a¨ananen and Koivistoinen, 1996). A fundamental change in milk pricing in the U.S. was introduced January 1, 2000, with the implementation of producer payments in Federal Milk Marketing orders on the basis of the true protein content (American Jersey Cattle Association, n.d.; Stephenson et al., 2004; Zhao et al., 2010).” (Sáez-Plaza, et al, 2013)
“The protein content in a foodstuff is estimated by multiplying the nitrogen content by a nitrogen-to-protein conversion factor, usually set at 6.25 (Comprehensive Review of Scientific Literature . . . , 2006; Mariotti et al., 2008), which assumes the nitrogen content of proteins to be 16%. It is not clear who first reported such a factor for use (Moore et al., 2010). This general conversion factor is used for most foods because their non-protein content is negligible. However, pure proteins differ in terms of their nitrogen content because of differences in their amino acid composition, ranging from 13.4% to 19.3%; different multiplying factors are suitable for samples of different kinds. The factor 5.7 is applied for wheat and 6.38 for dairy products (O’Sullivan et al., 1999) and 6.394±0.004 for cheddar cheese, as shown recently (Rouch et al., 2008). The proximate system where protein is measured as total nitrogen multiplied by a specific factor clearly dominates food composition studies (Greenfield and Southgate, 2003). As a matter of fact, most cited values for protein in food composition databases derive from total nitrogen or total organic nitrogen values.” (Sáez-Plaza, et al, 2013)
“A large variety of food proteins, either from animals (milk, meat, eggs, blood, fish) or plants (seeds, cereals), is nowadays available in the food industry. The determination of protein in foods and food products has important nutritional, functional, and technological significance (Van Camp and Huyghebaert, 1996). The protein content determines the market value (Krotz et al., 2008; Wiles et al., 1998) of major agricultural commodities (cereal grains, legumes, flour, oilseeds, milk, and livestock feeds). In addition, the quantitative analysis of protein content is necessary for quality control, and also a prerequisite for accurate food labelling (Owusu-Apenten, 2002). Protein analysis is required for a very wide range of animal and human nutrition products. Consumer interest in soy protein products has increased rapidly in Western cultures in recent years. This trend is due in part to the high-quality protein of soy foods and soy protein ingredients and in part to their associated health benefits (Jung et al., 2003); 25 g of soy protein per day may improve cardiovascular health (U. S. Food and Drug Administration, 1999). Consequently, precise determinations of protein content of soy products are very important. Total nitrogen concentration in soils is one of the most frequently measured nutrients in soil-testing laboratories (Sharifi et al., 2009). Determination of nitrogen content plays a key role in assigning values to insulin reference materials (Anglow et al., 1999). Primarily devised for the determination of protein nitrogen, the Kjeldahl method has been extended to include the determination of various other forms of nitrogen, e.g., in soils, plant materials, biological tissues, and wastewater matrices (Chemat et al., 1998). (Sáez-Plaza, et al, 2013)
“Though the Kjeldahl procedure is hazardous, lengthy, and labour-intensive, it has become the industry standard; it remains an accurate and reliable method and is used to standardize other methods (ISO, 2009a, 2011; Orlandini et al., 2009a; Orlandini et al., 2009b; Rayment et al., 2012). Semiautomated or fully automated nitrogen (protein) analysis systems based on the classical Kjeldahl procedure (Rhee, 2001; Wright and Wilkinson, 1993) are preferable in order to cut costs and to save time when a large number of samples need to be analyzed.” (Sáez-Plaza, et al, 2013)
The automation of chemical methods used routinely in research can lead to a considerable saving in time and labor and, thus, efficiency in carrying out a particular piece of work (Davidson et al., 1970; Feinberg, 1999). Automation makes it possible to avoid direct handling of dangerous reagents (Pansu and Gautheyrou, 2006), such as boiling sulfuric acid or concentrated soda. Ferrari (1960) succeeded in automating the Kjeldahl nitrogen procedure, describing the new concept of continuous nitrogen determination. The automated macro Kjel-Foss analyzer was introduced in 1973, with which one can routinely perform 20 analyses/hour (Oberreith and Neil, 1974). Various degrees of automation are available for the Kjeldahl method, including automated digestion and distillation followed by manual titration; fully automated digestion, distillation, and titration; and the use of block digesters and autosamplers for the unattended analysis of a maximum of 60 samples per batch. Semiautomated equipment is available with digestion and distillation determination units at macroscale and microscale from, for example, the manufacturers Bicasa, B¨uchi, Gerhardt, Skalar, Foss- Tecator, and Velp (Pansu and Gautheyrou, 2006; Pansu et al., 2001). Depending on the analysis procedure used, the scale of operation applied, and the degree of automation installed, the analysis time of the procedure could be further reduced, corresponding to frequencies of analysis up to 20 samples/hour.” (Sáez-Plaza, et al, 2013)
An important feature of the Proximate Analysis is the conversion of measured nitrogen to protein by multiplying total N by a factor to estimate the total protein content. It is still used for its simplicity and relative accuracy. The commonly used factor is 6.25 derived from the fact that protein contains 16% nitrogen. 100/16 = 6.25. Who the first person is to use this factor is not known. N in food can be measured by the Kjeldahl Method (1883) in which protein-N is dissociated from its combination with other elements by digestion in concentrated sulfuric acid (H2SO4) followed by conversion to the hydroxide and subsequent distillation and titration.” (Dryden, 2008)
“Jones, Munsey and Walker (1942) measured the nitrogen content of a wide range of isolated proteins and proposed a series of specific factors for different categories of food. These factors have been widely adopted and were used in the FAO/WHO (1973) review of protein requirements. These are listed in the table below. Several authors have criticized the use of these traditional factors for individual foods (e.g. Tkachuk, 1969). Heidelbaugh et al. (1975) evaluated three different methods of calculation (use of the 6.25 factor, use of traditional factors and summation of amino acid data) and found variations of up to 40 percent. Sosulski and Imafidon (1990) produced a mean factor of 5.68 based on the study of the amino acid data and recommended the use of 5.70 as a factor for mixed foods.
In principle, it would be more appropriate to base estimates of protein on amino acid data (Southgate, 1974; Greenfield and Southgate, 1992; Salo-Väänänen and Koivistoinen, 1996) and these were incorporated in the consensus document from the Second International Food Data Base Conference held in Lahti, Finland, in 1995, on the definition of nutrients in food composition databases (Koivistoinen et al., 1996).
If these recommendations are to be adopted, the amino acid data should include values for free amino acids in addition to those for protein amino acids because they are nutritionally equivalent. The calculations require very sound amino acid values (measured on the food) as discussed below, and involve certain assumptions concerning the proportions of aspartic and glutamic acids present as the amides and correction for the water gained during hydrolysis. Clearly, this approach would not be very cost-effective when compared with the current approach.
At the present time, it is probably reasonable to retain the current calculation method, recognizing that this gives conventional values for protein and that the values are not for true protein in the biochemical sense. However, it is important to recognize also that this method is not suitable for some foods that are rich in non-amino non-protein nitrogen, for example, cartilaginous fish, many shellfish and crustaceans and, most notably, human breast milk, which contains a substantial concentration of urea.
Factors for the conversion of nitrogen values to protein (per g N)*
Meat and fish
Milk and milk products
Rice and rice flour
Rye and rye flour
Barley and barley flour
* (Where a specific factor is not listed, 6.25 should be used until a more appropriate factor has been determined.)
Source: FAO/WHO, 1973.
A number of direct methods for protein analysis have been developed for specific foods based on reactions involving specific functional groups of the amino acids present; these are thus not applicable to the measurement of proteins in general. Such methods include formol titration (Taylor, 1957) and the biuret reaction (Noll, Simmonds and Bushuk, 1974). A widely used group of colorimetric methods is based on reaction with Folin’s reagent, one of the most widely used biochemically in the dairy industry (Lowry et al., 1951; Huang et al., 1976). These methods are most commonly calibrated with bovine serum albumin, which is available at high purity.” (Greenfield and Southgate, 2003)
Nutrient makeup of proximate principles
The Proximate Analysis is not used for deriving nutritional values, but it is still important, before leaving this subject, that we should specifically relate it to several nutrients. “We shall thus also delimit the extent to which the Weende scheme can be expected usefully to describe specific nutrients and groups of nutrients found in the animal body and in its food.” (Loyed, et al. 1960) I quote this from Loyed, et al. who was published in the 1960s. Despite the age of the work, I find it remarkably complete as an introduction to the subject.
“Carbohydrates The total number of edible materials that are carbohydrate by definition is large. There are, for example, a dozen or more that are found in everyday foods, either as one of six or seven “sweet” sugars, or in combinations of them comprising numerous more complex molecules such as the starches, hemicelluloses, or celluloses. The monosaccharide sugars are classified according to the number of carbon atoms in their molecules. Thus there are 5-carbon or pentose sugars, and 6-carbon or hexose sugars. All pentose sugars have the same empirical formula, C5H10O5; the empirical formula for all hexoses is C6H12O6. The complex carbohydrates are merely polymers of the simple sugar units, as (C5H8O4)n or (C6H10O5)n. Cellulose, for example, has been estimated to consist of 1000-2000 hexose units polymerized into the long fibrous chains characteristic of the cellulose structure. The distribution of the carbohydrates between the Weende nitrogen-free extract and crude fibre fractions is shown in the table below.” (Loyed, et al. 1960)
“It will be seen that the carbohydrate portion of our foods and feeds consists either of single 1-carbon or 6-carbon units or of larger molecules formed by combinations of such structures. Before the larger molecules can be useful in nourishing the body they all must be degraded by enzymes in the digestive tract to their simple 5- or 6-carbon units; or, in the case of cellulose and perhaps of some of the hemicelluloses, to either the 2-, 3-, or 4-carbon molecules of acetic, propionic, or butyric acids, respectively. (These three acids are products of digestion by microflora inhabiting the digestive system of animals, such as herbivores.)” (Loyed, et al. 1960)
“The nutritional significance of the fact that carbohydrates are all assemblies of 5- or 6-carbon units is that they have potentially about the same energy value, roughly between 3.75 and 4.25 kilocalories per gram of dry substance. Except for small amounts of ribose, carbohydrates can be considered useful primarily as sources of energy. These facts make it clear that even though the carbohydrate portion of a food or a diet is estimated “by difference” in the Ween de scheme of analysis, little if any, useful information is lost by this group treatment.” (Loyed, et al. 1960)
“The digestible or the metabolizable energy the body ultimately obtains from the nitrogen-free extract, from the crude fibre, or from the total carbohydrate (i.e., the nitrogen-free extract plus the crude fibre) of a food, is a somewhat different matter since the completeness of the digestion of these two groups of carbohydrates is often appreciably different. This matter will be considered later when the question of digestibility is dealt with. For the moment it will suffice to note that celluloses and hemicelluloses yield less useful energy to nonherbivores than do the carbohydrates of the nitrogen-free extract category.” (Loyed, et al. 1960)
Crude protein is also a group name; it refers collectively to the sum of up to 20 nutrients, the amino acids, each of which has one or more specific roles in metabolism. In addition, each of these protein components, if present in excess of that needed for its specific function, may, following absorption, be split into a nitrogen-containing entity NH3 and a daemonized residue, the latter becoming a nonspecific source of energy.” (Loyed, et al. 1960)
“Most of the amino acid residues that can be metabolized for energy contain 3-carbon atoms. In any case, only that fraction of an amino acid that is equivalent to some intermediate in the metabolism of sugars (or of fats) is so used. However, the potential energy in proteins, as measured by their complete combustion in a bomb calorimeter, is considerably greater than that in carbohydrates. This is true because, with protein, oxygen is required not only – to oxidize the carbon, but, unlike carbohydrates, is required also to oxidize some of the hydrogen atoms; and the heat of water formation is much higher than that of carbon dioxide. Thus, typical pure proteins yield 5.25-5.75 kilocalories of gross energy per gram.” (Loyed, et al. 1960) “Nevertheless, the amount of nutritionally useful energy of protein is not greatly different from that of carbohydrate. This is so because the amino group that is split off in the deaminization of each “discarded” amino acid forms urea, which is eliminated in the urine. Urea contains combustible carbon and hydrogen, and this part of the potential energy from protein is lost the body. In humans it amounts to about 1.25 kilocalories per gram of protein so that the maximum usable energy from typical protein does not exceed 5.50 – 1.25 or 4.25 kilocalories per gram; this is usually reduced further by the incompleteness of digestion to about 4 kilocalories per gram. This can be stated in another way: whereas carbohydrate yields to the body, on average, about 95% of its potential energy, only some 70% of the potential energy of protein can be used to meet energy needs. Protein is obviously not normally the preferred source of energy in nutrition.” (Loyed, et al. 1960)
“Incidentally, crude protein, by itself, describes only the energy of this nitrogenous fraction of foods. Without other information, the figure for the amount of crude protein in a food gives no reliable clue to the makeup of its nutrient units, the amino acids. Of these acids, we shall learn more later. It is sufficient here to tabulate them as some of the nutrients that we must deal with in nutrition (see table below).” (Loyed, et al. 1960)
Lipids, fats, and ether extract “In a beginning course in nutrition there is a tendency to use almost interchangeably the terms lipid, fat, and ether extract. In particular, when we record the total of the ether extractives, We often designate it merely as fat. This rather loose usage of these terms does not often lead us astray, for reasons that will become obvious as one delves deeper into the subject. But it may be well at the outset to define these terms in a more specific way, in order to have a clearer conception of what substances are included in that fraction of the Weende analysis called ether extract.” (Loyed, et al. 1960)
“Lipids Ure naturally occurring substances soluble in organic solvents, such as diethyl ether. A classification of these substances is given in the table below.” (Loyed, et al. 1960)
Calorie value of ether extract “This classification does not include all of the substances that may be found in the ether extract of foods or of tissue of the animal body. In general, the presence of substances other than triglycerides in ether extract dilutes its useful energy. They are mentioned here chiefly to show what a mixture the ether extract of foods may be. In foods of animal origin, such as meat fats, lard, or butter, it may be composed almost entirely of triglycerides. But in foods of plant origin, as much as half the total ether extract may be composed of sterols, waxes, and various other lipids. Since the nonglyceride lipids yield little utilizable energy to animals, the caloric value of ether extract is characteristic of specific foods: a single energy value, such as 9 kilocalories metabolizable energy per gram, while perhaps satisfactory for the fats of animal origin, the refined vegetable oils, or the shortenings prepared from them, is usually too high for the ether extract of foods of plant origin.” (Loyed, et al. 1960)
“The usefulness of the ether extract of the Weende scheme as a source of energy is dependent almost entirely on its total content of triglycerides. Ether extract values by themselves give no indication of the particular fatty acids in the fraction, nor of the amount of nonglyceride lipid. These values, therefore, are only an indication of the energy of a feed, which in turn is subject to considerable variation from one type of feed to another because of the possible variation in the composition of the lipid fraction.” (Loyed, et al. 1960)
Ash-the inorganic nutrients “The Weende analysis includes an inorganic fraction-the total of the noncombustible substances of the material. The quantity of ash in a feed or in some biological product does not of itself give information about any specific nutrient, and frequently the figure is used only to calculate the amount of carbohydrate by difference. The combination of mineral elements found in foods of plant origin is so variable that the ash figure of our analysis is useless as an index of the quantity of any particular element, or even of the total of the nutritionally essential ones. In the case of certain animal products, such as bone, milk, or cheese, whose composition is relatively constant, the approximate quantities of calcium and phosphorus can be predicted from the total ash figure. Thus, so far as useful information about the inorganic nutrients of foods is concerned, the ash figure is merely a starting point for specific analysis for one or another of some 21 to 26 mineral elements required by the body, and for a few about which information may be needed because of their toxic nature.” (Loyed, et al. 1960)
Classification of the nutrients
“To summarize this what we discussed here, the table below identifies the principal nutrients by name and indicates the fractions of the Weende analysis into which they fall.”
“The table makes it clear that the Weende analysis does not describe nutrients individually; when this is necessary, some other scheme of description must be used. But, in spite of limitations, the Weende analysis is the basis for the everyday chemical description of foods, body tissues, and excreta that are of concern in such calculations as the estimation of digestibility and utilization of foods and the establishment of feeding standards for all animal species.” (Loyed, et al. 1960)
The young man who took over from me as production manager at Woody’s Consumer Brands has a saying that managing a production department of a meat factory is a team sport. On the one hand, one needs the experienced manager’s approach of Albrecht Daniel von Thaer. On the other hand, I know from first-hand experience the financially devastating effect if a management team gets a call on a scientific matter related to meat science wrong. Managing a large food manufacturing concern is the job of an experienced team, not a lone ranger or a single night in shining armour and discipline in science and discipline in management has equally valid places.
A week ago an old friend visited from the United States and as we discussed these matters he commented that no matter what detours we take, we seem to always get back to clear management principles laid down by people like Peter Drucker. The study of the development of the proximate analysis and the examples of marrying good management and science as exemplified in the life of Carlsberg come to us through our analysis of the history of what led us to our current day determination of meat content in formulations. It is a subject so rich. We gain from it on every level.
(c) eben van tonder
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Bacon and the art of living is a study in the birth of the elements of bacon curing. Neither the chemical reactions, nor the different mechanical processes are simple. Everything about bacon is complex and beautiful. One of the most amazing stories within the grand story of bacon, is the story of sodium nitrite.
Pork is changed into bacon by the reaction of nirtrite (NO2-). With salt, it is the curing agent. The meat industry uses nitrite in the form of an ionic compound, sodium nitrite. It is sold as Quick Cure or Insta’ Cure, Prague Salt, Prague Powder or simply Pink Salt or Curing Salt. It is coloured pink to distinguish it from ordinary salt (sodium chloride). Every spice company sells it. It is the essential ingredient in the meat curing process.
Meat changes colour from the red fresh meat colour to an unappetising brown colour within days. (1) If one injects nitrite into the meat or rubs a mixture of salt and a small percentage of nitrite onto it, the meat will develop an appatizing reddish/ pinkish fresh meat colour (Hoagland, Ralph. 1914) and a characteristic cured taste. It will retain this colour for weeks and months if packed in the right conditions. (1) Nitrite provides an indispensable hurdle against a particularly nasty food pathogen, clostridium botulinum. It also endows the meat with a distinct cured taste.
During ages past, it has however not been nitrite that was added to meat to accomplish this, but its cousin, nitrate (NO3-). They may be cousins, but are very different in characteristics. Nitrate takes several weeks or even months to cure meat where nitrite accomplishes the same task in 12 hours. How the change happened from using nitrate or salpeter in meat curing to nitrite is an epic story.
This article tracks the migration of the meat industry from the use of saltpeter (potassium or sodium nitrate) as curing agent to sodium nitrite. It gives an overview of the scientific discoveries which started to reveal the mechanisms of meat curing. This understanding lead to the realisation that a direct application of nitrite as the curing agent will be vastly superior to the use of saltpeter (nitrate).
This was a dramatic discovery since in the late 1800’s and early 1900’s, the world saw nitrite as a dangerous drug at best and a poison that polluted drinking water and cause death of cattle. Using this directly in food and meat curing was unthinkable.
Sodium nitrite was available in this time for application in the coal-tar dye and medical industries. Science and engineering have however not worked out its large scale production in a way that will make it a commercially viable proposition for direct use in meat curing from a price and availability perspective.
World War One provided the transition moments required to change everything. Germany invested heavily in nitrogen related technology for the war. The most organised scientific and engineering environment on the planet in the early 1900’s focused its full attention on overcoming the manufacturing challenges in the service of the manufacturing of munitions. It also required this technology to overcome the challenge of being cut off, as a result of the war, from the natural sodium nitrate deposits in Chili that it required as fertilizer to drive its enormous agriculture sector during the war. At the same time, the use of saltpeter in meat curing was prohibited under the leadership of Walther Rathenau so that the valuable nitrate could be reserved for manufacturing of munitions.
This prohibition, I believe, was the initial spark that caused butchers to change to the use of sodium nitrite. At the same time, sodium nitrite was being produced in large volumes since it had, in its own right, application in the manufacturing of explosives. Health concerns and probably the need to have it reserved for munitions, lead to a ban, similar to nitrate, on its use in meat curing. So, World War One solved the scientific challenges of large scale manufacturing of sodium nitrite, the engineering challenges of building production facilities and provided the impetus for the meat industry to change by banning the use of saltpeter in meat curing. The ban was lifted after the war.
Following the war, Germany had to find markets for its enormous war time chemical stock piles. One of the ways it “sold” sodium nitrite was as a meat curing agent based on its inherent benefits of curing consistency and the vastly shorter curing time required.
It was introduced to the world mainly through the Chicago based firm, Griffith Laboratories, who imported it as Prague Salt from Germany and later improved on it by fusing the sodium nitrite to sodium chloride and sold it as Prague Powder.
Early humans to Polenski (1891)
Early humans did not know they added nitrate to the meat. A mixture of salt and a small amount of saltpeter was used to cure meat in order to preserve it and to retain the fresh meat colour.
Saltpeter is found naturally around the world in typically dry areas. Deposits exist in India, China, Mexico, the USA, and the Middle East. Despite its wide occurrence, the concentration of natural saltpeter is low. (Whittaker, CW, 1932: 10)
Saltpeter is also made by human effort. Europe, particularly Germany and France, Great Britain, India and the United States all acquired the technology to produce satpeter. (Van Cortlandt, P, 1776: 7, 8)
In South Africa, saltpeter deposits are found in the Griquatown beds of the Transvaal geological system. It extends from just South of the Orange River Northwards to the Kalahari Desert and then Eastwards into the Old Transvaal from Zeerust to Polokwane. The nitrate deposits occur in the middle portions of these beds, in softer and more decomposed shale. These South African reserves have fortunately never been mined even though it was used on a small scale to make gunpowder for the old Boer government. (Whittaker, CW, 1932: 10)
Saltpeter was at the heart of the arms race of the middle ages. It was used mainly in gunpowder, but as the worlds population grew, it became indispensable as a fertilizer and for curing meat. (See Bacon and the art of living, chapters 2, 3 and 4)
The French chemist, Antoine Lavoisier worked out its chemical composition. It is an ionic compound consisting of the metal potassium and its power is nitrate. Potassium Nitrate. (Mauskopf, MSH. 1995: 96) Trade in Saltpeter around the world was done through companies such as the Dutch East Indian Company (Dutch abbreviation, VOC) who traded it for its main use as an ingredient in gunpowder. It was by volume one of the largest commodities traded by the Dutch East Indian Company who set up the trading post in 1652 that became Cape Town.
Major developments shifted the balance of power away from Indie, China and home grown saltpeter production to South America where huge deposits of sodium nitrate were discovered that would become the principal source of the worlds nitrate for much of the 1800’s.
A popular legend tells the story of the discovery by two Indians in the Atacama desert in the South of Peru. According to the legend, after a hard day’s work, they camped in the Pampa and started a campfire to warm themselves. All of a sudden the ground started to burn and they ran away, thinking that they have seen the devil. They reported the event later to a priest in Camina who returned to the site. He had it analysed and found it to contain sodium nitrate (the same power as potassium nitrate, but linked to another common metal). The priest, according to the story, threw the rest of the soil in the courtyard of his house and saw the plants grew vigorously. He recommended the soil as an excellent tonic for the plant kingdom. (Wisniak, J, et al., 2001 :433)
So was discovered the enormous sodium nitrate deposits of the Atacama desert. The fertilizer properties of the salt was known long before the 1600’s. There are references to saltpeter and the nitrate ground in 1604. During the time of the Spanish Conquest, in the 1700’s, miners working in the South of Peru realised that gunpowder could be manufactured from the material in the soil instead of potassium nitrate. (Wisniak, J, et al., 2001 :433)
A report published in 1803 by Juan Egana, Secretary of the Royal Court of Mines in Chile showed the Huasco region is “covered in a large part by a crust of niter salt, well crystallized, and several inches thick” (Wisniak, J, et al., 2001 :434)
The region was developed and by 1850 exports reached 24 000 tons/ year. In 1910 it was 2.4 million tons per year and by 1916, 3 million tons per year from 97 plants. (Wisniak, J, et al., 2001 :434)
By the beginning of the 1900’s the country buying the largest quantity of the Chilean saltpeter was Germany (Wisniak, J, et al., 2001 :434) who used it aggressively in their agriculture sector as fertilizer.
There is a close correlation between sodium and potassium nitrate. Its difficult to distinguish between sodium and potassium nitrate just by tasting it. Scientists were able to distinguish between the two compounds from the mid 1600’s and knew that sodium nitrate had a much greater ability to attract water (Whittaker, CW, 1932: 3). This made sodium nitrate a much better curing agent than potassium nitrate.
Nitrite was described in 1864 by the English Physiologist, B. W. Richardson. He outlined how to manufacture it and its chemical properties. (Wells, D. A., 1865: 233) Much earlier, in 1777 the prolific Swedish chemist Scheele,working in the laboratory of his pharmacy in the market town of Köping, made the first pure nitrite. (Scheele CW. 1777) He heated potassium nitrate at red heat for half an hour and obtained what he recognized as a new “salt.” The two compounds (potassium nitrate and nitrite) were characterized by Péligot and the reaction established as 2KNO3→2KNO2+O2. (Péligot E. 1841: 2: 58–68) (Butler, A. R. and Feelisch, M.)
The technology existed in the 1800’s to not only produce potassium nitrate (salpeter) and nitrite, but to also test for these.
Remember that curing up till 1890 has been attributed to saltpeter (potassium nitrate) or Chilean saltpeter (sodium nitrate). In 1891 a German food scientist, Dr Ed Polenski, working for the German Department of Health made an observation that would change the world while studying curing brines. When he tested the curing brine made from saltpeter and salt, days after it was made, he found nitrite to be present. This was surprising since saltpeter is potassium or sodium nitrate, not nitrite.
Dr Ed speculated that the nitrate (NO3-) was changed into nitrite (NO2-) through bacterial action, a reduction step between nitrate and nitrite that was well understood by this time. He had a hunch that nitrite is responsible for curing of meat and not the nitrate directly, as was previously thought.
From Polenski (1891) to WWI (1914 to 1918)
Following Dr Ed’s observations in 1891, considerable resources from around the world were dedicated to understand the chemistry of meat curing.
When World War One broke out, the concept of nitrite as curing agent (as opposed to nitrate) was firmly established.
Ralph Hoagland, Senior Biochemist, Biochemie Division, Bureau of Animal Industry, United States Department of Agriculture, published an article in 1914, Coloring matter of raw and cooked salted meats. In this article, he shows that nitrite as curing agent was a known and accepted fact by the outbreak of World War One (Hoagland, Ralph. 1914)
Readers who dont have an interest in the detailed description of the key discoveries may want to skip over the rest of this section altogether or glance over it generally. The goal of the section is to give the reader a sense of how firmly and universally the concept of nitrite as the curing agent was established by 1914. In the midst of the technical names and jargon, don’t lose the sense of the universal interest. The 1700’s, 1800’s and beginning of the 1900’s was a time when the average person was as interested in chemistry as we are today about communication and information technology.
The difference between nitrates and nitrites, for example, was taught in school curriculum. An article appeared in the Daily Dispatch in Brainerd, Minnesota in the 20’s, that gives as an example of a diligent high school student, that he or she would know the difference. (The Brainerd Daily Dispatch (Brainerd, Minnesota). 17 January 1923. Page 3.)
Following Dr. Polenski’s observation, the German scientist, Notwang confirmed the presence of nitrite in curing brines in 1892, as observed by Dr Polenski, but attributed the reduction from nitrate to nitrite to the meat tissue itself. The link between nitrite and cured meat colour was finally established in 1899 by another German scientist, K. B. Lehmann in a simple but important experiment.
Karl Bernhard Lehmann (September 27, 1858 – January 30, 1940) was a German hygienist and bacteriologist born in Zurich.
In an experiment he boiled fresh meat with nitrite and a little bit of acid. A red colour resulted, similar to the red of cured meat. He repeated the experiment with nitrates and no such reddening occurred, thus establishing the link between nitrite and the formation of a stable red meat colour in meat. (Lee Lewis, W., 1925: 1243)
In the same year, another German hygienists, K. Kisskalt, confirmed Lehmann’s observations but proved that the same red colour resulted if the meat was left in saltpeter (potassium nitrate) for several days before it was cooked. (Lee Lewis, W., 1925: 1243)
K. B. Lehmann made another important observation that must be noted when he found the colour to be soluble in alcohol and ether and to give a spectrum showing an absorption band just at the right of the D line, and a second band, often poorly defined, at the left of the E line. On standing, the color of the solution changed to brown and gave the spectrum of alkaline hematin, the colouring group (Hoagland, Ralph. 1914).
The brilliant British physiologist and philosopher, John Scott Haldane weighed in on the topic. He was born in 1860 in Edinburgh, Scotland. He was part of a lineage of important and influential scientists. (Lang, M. A. and Brubakk, A. O. 2009. The Haldane Effect)
J. S. Haldene contributed immensely to the application of science across many fields of life. This formidable scientist was for example responsible for developing decompression tables for deep sea diving used to this day. (Lang, M. A. and Brubakk, A. O. 2009. The Haldane Effect)
“Haldane was an observer and an experimentalist, who always pointed out that careful observation and experiments had to be the basis of any theoretical analysis. “Why think when you can experiment” and “Exhaust experiments and then think.” (Lang, M. A. and Brubakk, A. O. 2009. The Haldane Effect)
An interesting anecdote is told about him from the time when he was studying medicine in Jena. He apparently carefully observed the amount of beer being drunk, noting that the students on the average drank about 20 pints per evening.” (Lang, M. A. and Brubakk, A. O. 2009. The Haldane Effect)
Before we look at Haldene’s contribution, let us re-cap what has been determined thus far.
Polenski and Notwang discovered that nitrite were present in a mix of saltpeter and salt, after a while, even though no nitrite were present when the brine was mixed.
Karl Bernhard Lehmann linked nitrite conclusively with the reddening effect of fresh meat that was boiled in a nitrite and water solution with some free acid. He also showed that this does not happen if fresh meat is placed in saltpeter and water solution and boiled immediately. K. Kisskalt showed that the same reddening occurred if fresh meat is left in saltpeter for some time.
K. B. Lehmann managed to “isolate” the colour by dissolving it in ether and alcohol and analyze it spectroscopically.
What S. J. Haldele did was to apply the same rigor to cured meat and became the first person to demonstrate that the addition of nitrite to hemoglobin produce a nitric oxide (NO)-heme bond, called iron-nitrosyl-hemoglobin (HbFeIINO). (Lang, M. A. and Brubakk, A. O. 2009: 119)
Nitrite is further reduced to nitric oxide (NO) by bacteria or enzymatic reactions and in the presence of muscle myoglobin forms iron-nitrosyl-myoglobin. It is nitrosylated myoglobin that gives cured meat, including bacon and hot dogs, their distinctive red color and protects the meat from oxidation and spoiling. (Lang, M. A. and Brubakk, A. O. 2009: 119)
This is how he did it. He concluded (1901) that its red colour is due to the presence of the nitricoxid hemochromogen resulting from the reduction of the coloring matter of the uncooked meat, or nitric-oxid hemoglobin (NO-hemoglobin). (Hoagland, Ralph. 1914)
Remember the observation made by K. B. Lehmann that the colour of fresh meat cooked in water with nitrites and free acid to give a spectrum showing an absorption band just at the right of the D line, and a second band, often poorly defined, at the left of the E line. (Hoagland, Ralph. 1914)
Haldene found the same colour to be present in cured meat. That it is soluble in water and giving a spectrum characteristic of NO-hemoglobin. The formation of the red color in uncooked salted meats is explained by the action of nitrites in the presence of a reducing agent and in the absence of oxygen upon hemoglobin, the normal coloring matter of fresh meats. (Hoagland, Ralph. 1914)
Ralp Hoagland (1908) studied the action of saltpeter upon the colour of meat and found that its value as an agent in the curing of meats depends upon the nitrate’s reduction to nitrites and the nitrites to nitric oxid, with the consequent production of NO-hemoglobin. The red colour of salted meats is due to this compound. Hoagland conclusively shows that saltpeter, as such, has no value to preserve the fresh colour. (Hoagland, Ralph, 1914: 212)
The reason why the knowledge did not translate to a change in curing brines was very simple. The technology and infrastructure did not exist to produce enough nitrite commercially to replace saltpeter. This means that to produce nitrite was very expensive.
There were some attempts to capitalise on the knowledge gained. The German scientist, Glage (1909) wrote a pamphlet where he outlines the practical methods for obtaining the best results from the use of saltpeter in the curing of meats and in the manufacture of sausages. (Hoagland, Ralph, 1914: 212, 213)
Saltpeter can only effect the colour of the meat if the nitrate in the saltpeter is reduced to nitrite. Glage gives for the partial reduction of the saltpeter to nitrites by heating the dry salt in a kettle before it is used. It is stated that this partially reduced saltpeter is much more efficient in the production of color in the manufacture of sausage than is the untreated saltpeter. (Hoagland, Ralph, 1914: 212, 213)
The fear of nitrites
The lack of a large scale production process for sodium nitrite and the engineering to build these plants were however not the only factors preventing the direct use of sodium nitrite in meat curing brines. As one review literature from the late 1800’s and early 1900’s, one realises that a major hurdle that stood between the use of sodium nitrites in meat curing was the mistrust by the general public and authorities of the use of nitrites in food. The matter relate to the high level of toxicity of nitrite, a matter that will be dealt with separately in Bacon and the art of living.
The first recorded direct use of nitrite as a curing agent was in 1905 in the USA where it was used in secret. (Katina, J. 2009) The USDA finally approved its use as a food additive in 1906. (porkandhealth) This did not mean that the public would accept it.
Sodium Nitrite started to be used in this time as a bleach for flour in the milling industry. Several newspaper articles reveal public skepticism and the great lengths that the scientific community and industry had to go to in order to demonstrate its safety as a bleaching agent for flour. An article appeared in The Nebraska State Journal Lincoln, Nebraska on 29 June 1910 entitled, “All for bleached flour. No harm can come from its consumption says experts”. The article deals with a federal court case about the matter and interestingly enough, it seems from newspaper articles that the government was opposing its use. Many other examples can be sited.
There is a 1914 reference in the London Times that shows the general view of nitrite as not just restricted to the USA. The article appeared on 9 June 1914 and a reference is made to sodium nitrite where it is described as “a dangerous drug with a powerful action on the heart.” (The London Times. 1914. Page 118) The reference was to the use of nitrite for certain heart conditions.
It is interesting that sodium nitrite did not find an immediate application in the meat industry, even after it was allowed in 1906 in the USA.
In my view, this points to problems surrounding availability and price. If the issue was the public perception alone, this could have been overcome with a PR campaign by the meat industry as was successfully done by the milling industry.
On 13 Dec 1915 George F. Doran from Omaha, Nebraska, filed an application for a patent for a curing brine that contained nitrites. His application strengthens the evidence that it was not the knowledge of nitrite and its role in curing that was lacking, but availability and price. He states the objective of his patent application to “produce in a convenient and more rapid manner a complete cure of packing house meats; to increase the efficiency of the meat-curing art; to produce a milder cure; and to produce a better product from a physiological standpoint.”
One of Doran’s sources of nitrite is “sterilized waste pickling liquor which he [I have] discovered contains soluble nitrites produced by conversion of the potassium nitrate, sodium nitrate, or other nitrate of the pickling liquor when fresh, into nitrites. . .” “Waste pickling liquor is taken from the cured meats. Nitrites suitable for use in carrying out the present invention may be produced by bacterial action from nitrates and fresh pickling liquor by adding a small percentage of old used pickling liquor. The bacteria in old pickling liquor are reducing bacteria and change nitrates to nitrites.” (Process for curing meats. US 1259376 A)
The use of old pickle has been described much earlier than Doran’s patent. His usage of old pickle when he understood the reduction of nitrate to nitrite and nitrite’s role in curing along with the fact that sodium nitrite was available can point to only one reason – price. It comes 10 years after sodium nitrite was first tested in curing brines for meat and shows that it has never become the curing agent of choice most probably due to limited availability and price. Much more about this later.
The postWWI era (1918 and beyond)
After WWI something changed. Saltpeter (potassium or sodium nitrate) has been substituted by the direct addition of nitrite to the curing brines.
The question is who pioneered this. Why and how did sodium nitrite production become so commonplace that it became available to bacon curing plants around the world?
Industry developments like this do not happen “by itself.” Someone drives it in order for it to become general practice in an industry.
Chilean Saltpeter is a good case in point. Even though natural sodium nitrate deposits were discovered in the Atacama desert, it took a considerable effort on the side of the producers (mainly the Chilean Government) to work out the benefits of sodium nitrate and to market it to the world. It is, for example, famously reported that the first shipment to Britain was dumped in the sea before the ship docked on account that the cargo attracted customs duty and the ships owners could not see any commercial application for sodium nitrate. (2)
In the same way, the direct application of nitrite in curing brines must have been driven by someone.
The Griffith Laboratories, Inc.
The Chicago based company of Enoch Luther Griffith and his son, Carroll Griffith started to import a mixture of sodium nitrite and salt as a curing substitute for saltpeter from Germany in 1925. The product was called Prague Salt (Prague Powder, 1963: 3)
The Griffith Laboratories (3) played a key role in marketing the new curing brine in the USA. They took the concept of the Prague Salt (sodium nitrite) and in 1934 announced an improved curing brine, based on the simple use of sodium nitrite, where they fuse nitrite salt and sodium chloride in a particular ratio. They called it Prague Powder. Their South African agents, Crown Mills (4), brought the innovation to South Africa. (Prague Powder, 1963: 3, 4)
It is fair to assume that if Prague Salt was being sold to Griffith in the 1920’s, the German producers must have sold it to other countries and companies around the world also.
The benefits of Prague Salt and later Prague Powder over Saltpeter is dramatic. Prague Salt (sodium nitrite) does not have the slightly bitter taste of saltpeter (Brown, 1946: 223). It allows for greater product consistency since the same percentage of nitrate was not always present in the saltpeter and the reduction of nitrate to nitrite takes longer or shorter under various conditions (Industrial and Engineering Chemistry, December 1925: 1243). The big benefit was however in the curing time required. Instead of weeks or even months that is required with saltpeter, curing could now be done in days or even hours with sodium nitrite. (The Food Packer, 1954: 64) From there, brand names like Quick Cure or Instacure.
This means that we have narrowed the time line for invention of Prague Salt (Sodium Nitrite) to between 1914, the beginning of the Great War and 1925 when Griffith imported it from Germany.
However, a document, published in the USA in 1925 shows that sodium nitrite as curing agent has been known well before 1925.
The document was prepared by the Chicago based organisation, The Institute American Meat Packers and published in December 1925. The Institute started as an alignment of the meat packing companies set up by Phil Armour, Gustavus Swift, Nelson Morris, Michael Cudahy, Jacob Dold and others with the University of Chicago.
A newspaper article about the Institute sets its goal, apart from educating meat industry professionals and new recruits, “to find out how to reduce steers to beef and hogs to pork in the quickest, most economical and the most serviceable manner.” (The Indiana Gazette. 28 March 1924).
The document is entitled, “Use of Sodium Nitrite in Curing Meats“, and it it is clear that the direct use of nitrites in curing brines has been practiced from earlier than 1925. (Industrial and Engineering Chemistry, December 1925: 1243)
The article begins “The authorization of the use of sodium nitrite in curing meat by the Bureau of Animal Industry on October 19, 1925, through Amendment 4 to B. A. I. Order 211 (revised), gives increased interest to past and current work on the subject.”
Sodium Nitrite curing brines would therefore have arrived in the USA, well before 1925.
It continues in the opening paragraph, “It is now generally accepted that the salpteter added in curing meat must first be reduced to nitrite, probably by bacteria, before becoming available as an agent in producing the desirable red color in the cured product. This reduction is the first step in the ultimate formation of nitrosohemoglobin, the color principle. The change of nitrate to nitrite is by no means complete and varies within considerable limits under operating conditions. Accordingly, the elimination of this step by the direct addition of smaller amounts of nitrite means the use of less agent and a more exact control.”
Griffith describes the introduction and origin of Prague Salt and later, Prague Powder as follows in official company documents:
“The mid-twenties were significant to Griffith as it had been studying closely a German technique of quick-curing meats. Short on manpower and time, German meat processors began curing meats using Nitrite with salt instead of slow-acting saltpeter, potassium nitrate. This popular curing compound was known as “Prague Salt.” (Griffith Laboratories Worldwide, Inc.)
The World War One link
The tantalizing bit of information from Griffith sets World War One as the background for the practical and large scale introduction of direct addition of nitrite into curing brines through sodium nitrite.
There has to be more to the reason for saltpeter being replaced by sodium nitrite as curing agent than the reasons given by Griffith. For starters, the meat industry has always been under pressure to work fast with less people due to pressure on profit margins. The need to cure meat quicker due to short manpower and time as a result of the war could not be the full story.
The World War One link from Griffith does not give all the answers, but it puts the introduction of sodium nitrite to meat curing between 1914 and 1918, at least 7 years before Griffith started to import Prague Salt.
A document from the University of Vienna would fill out the story. According to it, saltpeter was reserved for the war effort and was consequently no longer available as curing agent for meat during World War One. (University of Vienna). It was reserved for the manufacturing of explosives, and for example, the important industry of manufacturing nitrocellulose, used as base for the production of photographic film, to be employed in war photography. (Vaupel, E., 2014: 462) It gets even better. Not only did the prohibition on the use of saltpeter expand the information from Griffith as to why people started using sodium nitrite (macro movements in culture does not take place because of one reason only), but it provide a name to the prohibition.
In August 1914, the War Raw Materials Department (Kriegsrohstoffabteilung or KRA) was set up under the leadership of Walther Rathenau. It was Rathenau who was directly responsible for the prohibition on the use of salpeter. (5) He therefore is the person in large part responsible creating the motivation for the meat industry in Germany to change from saltpeter to sodium nitrite as curing medium of choice for the German meat industry during Wold War One.
Walter Rathenau’s actions may have motivated the change, but it was the developments in synthesizing ammonia, sodium nitrate and sodium nitrite which provided the price point for the compound to remain the curing agent of choice, even after the war and after the prohibition on the use of saltpeter was lifted.
One ofthe most important scientific riddles to be solved in the late 1800’s/ early 1900’s was how to produce ammonia and its related chemicals from atmospheric nitrogen. Sir William Crookes delivered a famous speech on the Wheat Problem at the annual meeting of the British Association for the advancement of Science in 1898.
In his estimation, the wheat production following 1897 would seriously decline due to reduced crop yields, resulting in a wheat famine unless science can step in and provide an answer. He saw no possibility to increase the worlds wheat yield under the prevailing agricultural conditions and with the increase in the world population, this posed a serious problem. He said, “It is clear that we are taxed with a colossal problem that must tax the wits of the wisest.” He predicted that the USA who produced 1/5th of the worlds wheat, would become a nett importer unless something change. He pointed to the obvious answer of manure, but observed that all available resources are being depleted fast.
Sir William saw a “gleam of light in the darkness” and that “gleam” was atmospheric nitrogen. (Otago Witness. 3 May 1900, Page 4)
It was the German Chemist, Fritz Harber who solved the problem, with the help of Robert Le Rossignol who developed and build the required high pressure device to accomplish this. (www.princeton.edu)
In 1909 they demonstrated that they could produce ammonia from air, drop by drop, at the rate of about a cup every two hours. “The process was purchased by the German chemical company BASF (a coal tar dye supplier), which assigned Carl Bosch the difficult task of scaling up Haber’s tabletop machine to industrial-level production.Haber and Bosch were later awarded Nobel prizes, in 1918 and 1931 respectively, for their work in overcoming the chemical and engineering problems posed by the use of large-scale, continuous-flow, high-pressure technology.” (www.princeton.edu)
“Ammonia was first manufactured using the Haber process on an industrial scale in 1913 in BASF’s Oppau plant in Germany.” (www.princeton.edu)
It was the vision and leadership of Walther Rathenau, the man responsible for restricting the use of saltpeter, that drove Germany to produce synthesized Chilean Saltpeter. He saw this as one of the most important tasks of his KRA. He said: “I initiated the construction of large saltpeter factories, which will be built by private industries with the help of governmental subsidies and will take advantage of recent technological developments to make the import of saltpeter entirely unnecessary in just few months“. (Lesch, J. E., 2000: 1)
Fritz Harber was one of the experts appointed by Rathenau to evaluate a study on the local production of nitric acid.
During World War One production was shifted from fertilizer to explosives, particularly through the conversion of ammonia into a synthetic form of Chile saltpeter, which could then be changed into other substances for the production of gunpowder and high explosives (the Allies had access to large amounts of saltpeter from natural nitrate deposits in Chile that belonged almost totally to British industries; Germany had to produce its own). It has been suggested that without this process, Germany would not have fought in the war, or would have had to surrender years earlier.” (www.princeton.edu)
So it happened that Germany became the leader in the world in synthesised sodium nitrate production and it effectively replaced its reliance on saltpeter from Chile with sythesised sodium nitrate, produced by BASF and other factories.
So, as a result of the First World War, sodium nitrite was produced at levels not seen previously in the world and in large factories that was build, using the latest processing techniques and technology from a scientific and an engineering perspective. Sodium nitrite, like sodium nitrate was being used in the production of explosives. Nitroglycerin is an example of an explosive used extensively by Germany in World War One that uses sodium nitrite in its production. (Wikipedia.org. Nitroglycerin and Amyl Nitrite)
Sodium nitrite and the coal-tar dye industry
The importance of the manufacturing cost of nitrite and the matter surrounding availability can be seen in the fact that sodium nitrite has been around since well before the war. Despite the fact that it was known that nitrite is the curing agent and not nitrate, and despite the fact that sodium nitrite has been tested in meat curing agents, probably well before the clandestine 1905 test in the USA, it did not replace saltpeter as the curing agent of choice. My hunch is that it did not enter the meat industry as a result of cost.
The technology that ultimately is responsible for synthesising Chilean Saltpeter and made low cost sodium nitrite possible was being incubated in the coal-tar dye and textiles industry and in the medical field. The lucrative textiles and dye industry was the primary reason for German institutions of education, both in science and engineering to link with industry, resulting in a strong, well organised skills driven German economy. For example, “Bayer had close ties with the University of Göttingen, AGFA was linked to Hofmann at Berlin, and Hoechst and BASF worked with Adolph Baeyer who taught chemists in Berlin, Strasbourg, and Munich.” (Baptista, R. J.. 2012: 6)
“In the late 1870s, this knowledge allowed the firms to develop the azo class of dyes, discovered by German chemist Peter Griess, working at an English brewery, in 1858. Aromatic amines react with nitrous acid to form a diazo compound, which can react, or couple, with other aromatic compounds.” (Baptista, R. J.. 2012: 6)
Nitrous acid (HONO) is to nitrite (NO2-) what nitric acid (NO3) is to nitrate (NO3-).
According to K. H. Saunders, a chemist at Imperial Chemical Industries, Ltd., Martius was the chemist to whom the introduction of sodium nitrite as the source of nitrous acid was due. (Saunders, K. H., 1936: 26)
The economic imperative
The simple fact is that ammonia can be synthesized through the direct synthesis ammonia method at prices below what can be offered through Chilean Satlpeter. (Ernst, FA. 1928: 92 and 100) Sodium Nitrite can be supplied at prices below Chilean saltpeter and this made sodium nitrite the most effective curing agent at the lowest price since World War One.
As an example of the cost differences, the price of Nitric Acid (HNO3) from direct synthesis in 1928 was $23.60 per ton HNO3 plus the cost of 606 lb. of NH3 by-product and from Chilean Nitrate at $32.00 per ton of HNO3, plus the cost of 2840 N NO3 by-product. (Ernst, FA. 1928: 112)
The advantage of scale and technology
By 1927, Germany was still by far the worlds largest direct syntheses ammonia producer. Production figures of the year 1926/ 1927 exceeded Chilean saltpeter exports even if compared with the highest levels of exports that Chilean saltpeter ever had in 1917. A total of 593 000 tons of nitrogen was fixed around the world in 1926/27. Of this figure, Germany produced 440 000 tons or 74%. The closest competitor was England through the Synthetic Ammonia and Nitrates Ltd. with a total capacity of 53 000 tons of nitrogen per year. (Ernst, FA. 1928: 119, 120)
In the USA 7 direct synthesis plants were in operation with a combined capacity of 28 500 tons of nitrogen per year. (Ernst, FA. 1928: 120)
Supporting evidence from the USA
The thesis that before the war, the production of sodium nitrite was not advanced enough for its application in the meat industry (resulting in high prices and low availability) is confirmed when we consider the situation in the USA.
The first US plant for the fixation of atmospheric nitrogen was build in 1917 by the American Nitrogen Products Company at Le Grande, Washington. It could produce about one ton of nitrogen per day. In 1927 it was destroyed by a fire and was never rebuild. (Ernst, FA, 1928: 14)
An article in the Cincinnati Enquirer of 27 September 1923 reports that as a result of cheap German imports of sodium nitrite following the war, the American Nitrogen Products Company was forced to close its doors four years before the factory burned down. The imports referred to, was as a result of Germany selling their enormous stockpiles of sodium nitrite at “below market prices” and not directly linked to a lower production price in Germany, even though this was probably the case in any event. ( The Cincinnati Enquirer ( Cincinnati, Ohio), 27 September 1923. Page 14.)
The Vienna University document indicate that the fast curing of sodium nitrite was recognised and the ban was lifted when the war ended. It was this fact that Griffith picks up on in their literature.
This is how it happened that sodium nitrite replaced saltpeter as curing salt.
The ban on the use of saltpeter for non military uses by Walther Rathenau is the likely spark that caused butchers to look at alternative curing systems. A known alternative was sodium nitrite. Despite a similar ban on the use of nitrite, later imposed for concerns over the safety of nitrite in meat and because sodium nitrite was also used to produce explosives, it was available in such large quantities around Germany that it was possible to defy the ban.
The likely consequence of the developments surrounding the production of atmospheric nitrogen is that sodium nitrite was being produced at prices that was previously not possible. These prices, combined with the volume of sodium nitrite now available made it a viable proposition to replace saltpeter in meat curing and to remain the curing brine of choice, following the war.
(1) “The red color of fresh lean meat, such as beef, pork, and mutton, is due to the presence of oxyhemoglobin, a part of which is one of the constituents of the blood remaining in the tissues, while the remainder is a normal constituent of the muscles. When fresh meat is cooked or is cured by sodium chloride, the red color changes to brown, owing to the breaking down of the oxyhemoglobin into the two constituents, hematin, the coloring group, and the protein, globin.
On the other hand, when fresh meat is cured by means of a mixture of sodium chloride and a small proportion of potassium nitrate, or saltpeter, either as a dry mixture or in the form of a pickle, the red color of the fresh meat is not destroyed during the curing process, the finished product having practically the same color as the fresh meat. Neither is the red color destroyed on cooking, but rather is intensified.” (Hoagland, Ralph. 1914)
(2) The first export of salitre (sodium nitrate) was authorised by the Chilean government in March 1830 and went to the USA, France, and to Liverpool. It is the latter shipment which failed and was thrown overboard. Different sources give different reasons for the action. One, that price was not attractive, another, that the excise duties were to high, and a third that the Port captain did not allow the boat to come in because it was carrying a dangerous load. A few farmers in Glasgow received a few bags. They used it as fertalizer and reported a three fold increase in crop yield. (Wisniak, J, et al. 2001: 437)
(3) Steve Hubbard, Vice President, Global Marketing and Innovation at Griffith Laboratories Worldwide, Inc. graciously provided me with much of the information from company documents.
(4) Crown Mills was bought out by Bidvest and became Crown National.
(5) The first War Raw Materials Department (KRA) in Germany was created (KRA) in mid-August 1914, as suggested by Walther Rathenau. (Vaupel, E. 2014: 462) Walter was the son of the founder of AEG and “one of the few German industrialists who realized that governmental direction of the nation’s economic resources would be necessary for victory, Rathenau convinced the government of the need for a War Raw Materials Department in the War Ministry. As its head from August 1914 to the spring of 1915, he ensured the conservation and distribution of raw materials essential to the war effort. He thus played a crucial part in Germany’s efforts to maintain its economic production in the face of the tightening British naval blockade.”
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