Counting Nitrogen Atoms – The History of Determining Total Meat Content (Part 4): The Background of the History of Nutrition
By: Eben van Tonder
For part 1, 2 and 3, click on:
As background to the Kjeldahl method of nitrogen determination and the Jones factors, commonly used to determine lean meat content, we look at the history of the discovery of nitrogen in protein. These methods link the relatively fixed proportion of nitrogen in protein to the calculation of protein content and are the basis of the determination of lean meat content.
The background story of nitrogen and protein is told through two lenses as described by two giants in science. The lens we concluded within our last installment is the history of unraveling protein metabolism up to the early 1960s. I relied mostly on the work of Hamish Nisbet Munro who was described in a biography written for the National Academy of Sciences by Robert M. Russell and Nevin S. Scrimshaw as “by far this generation’s most illustrious and productive expert on mammalian protein metabolism.” In one of the closing paragraphs of the previous article, I quoted Hamish when he wrote, that in “1810 Gay-Lussac, pupil of Lavoisier’s colleague, Berthollet, devised a system of analysis of organic compounds which allowed the identification of the nitrogen-rich organic compounds we know as the proteins . . . To the laboratory of Gay-Lussac came the young Liebig in 1823, to take back to Germany the new science of organic analysis and apply it to the study of biological materials. In Munich, Liebig had in 1854 as a pupil in his class in chemistry Carl Voit, who was to lay the foundations of modern studies on nitrogen balance. In Voit’s laboratory, numerous investigators from Germany and from abroad underwent a period of training—including Rubner, who especially studied the specific dynamic action of proteins; Atwater and Lusk, who continued the study of protein metabolism in America; and Cathcart, who returned to Scotland and was the teacher” of none other than Hamish Munro himself, thus endowing him with the best possible credentials to tell the story.
“In 1946, Hamish received his first grant from the British National Research Council
and set up a research unit at Glasgow University to study metabolic responses to injury. He then accepted a position as assistant professor in the Physiology Department at Glasgow University and transferred to the Biochemistry Section, where he remained for 20 years, during which time he rose to the rank of professor. Throughout this period, Hamish continued his studies on protein metabolism and also ventured into the investigation of nucleic acids and protein metabolism. Toward the end of this time, he completed his first two volumes of Mammalian Protein Metabolism, coauthored with James B. Allison.” (Russel and Scrimshaw, 2014) It was the last section of his first chapter of this work that we quoted in its entirety in our 3rd installment of “Counting Nitrogen Atoms – The History of Determining Total Meat Content.” In 1966 Hamish was recruit as professor of nutritional biochemistry and metabolism in MIT’s new Department of Nutrition and Food Science.
The second lens that we used to look at the history of nitrogen and protein and our historic understanding of the relationship between the two is through the unfolding history of nutrition. Here we relied mostly on the work of another icon in the scientific community namely Kenneth Carpenter.
Kenneth . . . “was an eminent British nutrition scientist whose career, spanning approximately 60 years, was almost equally spent in the UK and the USA. In the UK, from 1946 to 1976, he focused on some of the key nutrition issues of the time, starting with B vitamins, including niacin, folic acid, and riboflavin, and moving on to the influence of processing and storage on protein quality. He pioneered the notion of nutrient bioavailability and the concept that a nutrient can be present in a foodstuff, as measured analytically, but is not absorbed and utilised because it is present in a non-digestible bound form. His research led to the identification of bound niacin in maize and explained why pellagra was common in most but not all maize-eating populations. He identified bound lysine in certain high-protein animal foods and explained why chickens and pigs fed rations based on ‘high-lysine’ fishmeals, meat meals or milk powder did not grow as well as would be expected. The Carpenter analytical method to measure available lysine in foods based on fluorodinitrobenzene (FDNB) is still a standard laboratory procedure. It has been used extensively in the milk industry to control lysine losses during heat processing so as to ensure the nutritional quality of infant formula and complementary foods.” (Hurrell, R. F., 2018) Kenneth was a historian of note even though he did not think of himself in those terms. “In the USA from 1977 onwards, he gradually moved from nutrition research to the history of nutrition as he became more interested in the evolution of ideas in nutrition science. He is credited as making this complex history widely accessible to both serious scholars and the general public through a series of highly acclaimed monographs and papers. In his work, he saw himself as a nutrition scientist rather than historian as he did not, as does the classical historian, use archival records as a source of his information but reviewed early published literature and presented the problem as seen in the publications of the time.” (Hurrell, R. F., 2018)
A moving obituary was published in the science column of The Guardian on Thursday, 12 January 2017 by Roger Carpenter. He noted about his style that “Kenneth wrote with both elegance and clarity.” It is this clarity that I enjoy in his work and will return to his work many times. His paper on the nutritive value of meat meals which was done in 1970 with Atkinson is of particular interest. There is his work on the impact of storage on protein quality, obviously of immense interest. Another is his work on the influence of raw materials and processing on protein quality and the many articles on the effect of heat on protein will have to be digested fully at some stage so that we can glean the full value from the master.
He did four landmark articles entitled A Short History of Nutritional Sciences, Part 1, covering 1785–1885, Part 2, covering 1885–1912, Part 3, covering 1912–1944 and Part 4, covering 1945–1985. I already made extensive use of his work from part 1. Part 2 – 4 are equally applicable as vital background information to our present study. I decided to select information from these remaining 3 articles that directly speak to our subject of the history of the development our understanding of protein and in particular as it relates to the nitrogen content, in this section then, from the perspective of nutrition. In the next installment, I will directly move to the history of the Kjeldahl method of nitrogen determination and the Jones factors. A 6th chapter has to follow where we look critically at an evaluation of these methods of protein determination and better alternatives that emerged over the last few years.
The importance of a thorough understanding of protein in meat processing cannot be overstated since it is the essence of the subject matter. Its chemistry and physiology is the basis of every process and product. It is therefore fitting that in considering the determination of meat content, we should begin by reviewing how our current understanding of protein came about, both in terms of its metabolism and function in nutrition.
Young, John Richardson, (1782–1804). Found that regurgitated stomach contents did not undergo acetous fermentation.
William Beaumon, (1785 – 1853). Viewed as the father of gastric physiology, he observed that gastric juice, which always contained hydrochloric acid, was secreted only in response to eating. He also saw that oily food was only slowly digested, but that it was speeded by “minuteness of division”.
Claude Bernard, (1813 – 1871). Discovered that the secretions into the small intestine from the pancreas, together with the emulsifying effect of the bile, were of the greatest importance for the digestion of fat into glycerol and free fatty acids, and its absorption.
Wilbur Atwater, (1844 – 1907). A student of Carl Voit, Atwater estimated that American workmen were generally better off and ate more than German counterparts. He also thought they worked harder and he set his standard required protein intake per day at 125 g/d.
Russell Chittenden, (1856 – 1943). A professor of Physiological Chemistry at Yale University, we review some of his work on low protein diets.
We review the discovery of amino acids and its implications to the study of nutrition. The work of F. Gowland Hopkins (1861 – 1947) who the Nobel Prize in Physiology or Medicine in 1929, with Christiaan Eijkman, for the discovery of vitamins, and S. W. Cole who isolated tryptophan. The work of Wilcock and Hopkins in 1906 could show that mice lived longer on zein and tryptophan. Tryptophan became the first amino acid to be recognized as being essential for the normal growth of young animals.
We examine the work of William Cumming Rose (1887 – 1985) and colleagues who discovered the amino acid threonine and his research determined the requirement for essential amino acids in diets. Their work showed that mixtures of amino acids could replace protein completely in a diet.
We look at the unusual studies by Elsie Widdowson, (1906 – 2000) and dr. Robert McCance (1989 – 1993), responsible for overseeing the government-mandated addition of vitamins to food and wartime rationing in Britain during World War II.
Finally, we consider the state of the world in the 1960’s when a senior nutritionist said, “We have moved from the era of vitamin research to protein research,” and the head of the Nutrition Division of FAO (the Food and Agriculture Organization of the United Nations) wrote that, “deficiency of protein in the diet is the most serious and widespread problem in the world.” We end by concluding that measuring nitrogen and nutritional value of meat products is not just a matter of complying with government regulations but is a deeply moral question as well, deserving the NPD departments full attention.
The question of digestion had to be solved for is to understand how a balance of ingested nitrogen was possible. Kenneth brilliantly reviews the impact of the work of the work of the American, John Young at the beginning of the 1800’s who had found that regurgitated stomach contents did not undergo acetous fermentation, which was contrary to the current opinion. Then, some 20 years later there was William Beaumont who, as an army surgeon, “had the opportunity to become a pioneering physiologist. At a remote trading post a young man was accidentally shot in the stomach and the wound left a permanent fistula through which food samples could be introduced and removed. Because the victim was destitute, Beaumont took him into his house and used him as a subject intermittently for almost 10 y. He observed that gastric juice, which always contained hydrochloric acid, was secreted only in response to eating. He also saw that oily food was only slowly digested, but that it was speeded by “minuteness of division”.” (Carpenter)
“In the 1850s, “Claude Bernard discovered that the secretions into the small intestine from the pancreas, together with the emulsifying effect of the bile, were of the greatest importance for the digestion of fat into glycerol and free fatty acids, and its absorption. This and the later discoveries of the proteolytic activity in the small intestine, to be discussed later made the study of purely gastric digestion seem less important.”” (Carpenter)
Diseases Due to Nutritional Deficiencies
“In 1842 George Budd, Professor of Medicine at King’s College, London, gave a memorable lecture titled “Disorders resulting from defective nutriment,” from which these are some of his opening comments: “There is no subject of more interest to the physiologist or of more practical importance to the physician … than the disorders resulting from defective nourishment. … These disorders are, no doubt, frequently presented to us by the destitute poor in our large towns; but … from our not being acquainted with all the circumstances in which they arise, their real cause escapes us. It is only—as in ships, garrisons, prisons, and asylums—when large numbers of men … become affected with one disease, that our attention is fixed upon it, and that we can succeed in discovering its cause by considering what is peculiar in their circumstances”. (Carpenter)
An understanding emerged that protein and the accompanied measurement of the nitrogen content is not the only “wellness factor” in food. Kenneth brilliantly reviews the history of the development of the concept that nutrition is crucial to wellness at a time when the germ theory of disease was predominant.
Over the course of his life, he studied and wrote extensively on the history of the research into arctic scurvy, goiter, and cretinism, anemia among young women, beriberi, chicken polyneuritis, rickets in young children, infantile scurvy, adult scurvy, guinea pig scurvy, night blindness, and xerophthalmia and how the work on these contributed to our understanding of nutrition and its direct link to wellness. Its importance to our goal is that it neatly introduces the subject of vitamins, minerals, and different amino acids profiles of protein. This will especially become important in our next article when we evaluate the different ways that meat content can be measured and the total nutritional benefit of meat vs a plant-based diet.
Even looking back at the material we have covered so far, it explains some of the earlier results of animal studies that were fed only one kind of food in early “balanced trails” since the results may have been due to a vitamin deficiency and not protein deficiency.
Protein research continued
“Until this time, there had been little significant work in nutritional science in the United States, but Wilbur Atwater, born in 1844 in New England and by 1885, a professor of chemistry at Wesleyan University, was determined to change that. He had already spent several months in Munich studying the nitrogen balance procedures in use at the laboratory of Carl Voit, who had been Liebig’s protégé. Voit believed that people with sufficient income to choose the diet that they preferred would instinctively select a diet containing the amount of protein that they needed to remain healthy and productive. His estimate was that the average German workman doing moderate physical work chose to eat 118 g protein/d, and this became his standard. Atwater found that American workmen were generally better off and ate more. They also, he thought, worked harder and he set his standard at 125 g/d.” (Carpenter)
“With hindsight, it seems ironic that he should not have been more questioning concerning whether they really needed so much of this relatively expensive ingredient. Apparently, he looked to the German school of nutritionists as the authorities in a field in which he was only a newcomer. Voit accepted that vegetarians who lived on a much lower protein intake could remain in nitrogen balance, but he remained convinced that such people “exposed themselves to disadvantages”. The American group suggested that even if protein was not directly used as the fuel for muscular contraction, it provided the nervous energy required to “wish to make the effort”.” (Carpenter)
“The main thrust of Atwater’s work in this period was to analyze foods by the proximate system (nitrogen, fiber, ash, ether extract, moisture and “carbohydrate by difference”)) and to use these values to teach the poor how they could obtain their requirement for protein, the most expensive of their needs, more economically. An unfortunate effect of recommending diets only on the basis of the economic provision of protein and energy was that fruits and green vegetables became dispensable luxuries. At this period, the purchase of food typically took ∼50% of a working family’s income.” (Carpenter)
The challenge to high protein standards came finally from Russell Chittenden, Yale University’s Professor of Physiological Chemistry. He had found some relief from what may have been a rheumatic condition after he had deliberately reduced his general intake of food, and particularly that of meat, and was greatly impressed by having fully maintained both his physical and mental activity, although his intake of protein had not been >40 g/d (equivalent to 48 g for someone of the “standard” weight of 150 lb). (Carpenter)
“Chittenden then organized three controlled trials using low protein diets. In the first, Chittenden and three scientific colleagues remained healthy and in nitrogen balance for 6 mo on daily diets containing 62 g protein on average, after adjustment to “standard” body weight. The second trial used 11 corpsmen from the U.S. army who also remained in good health and physical condition with a standardized daily intake of 61 g protein. In the final trial, a group of 7 Yale student-athletes consumed ∼64 g protein (standardized) per day, maintained their levels of athletic performance and said that they felt better for it.” (Carpenter)
“Others were reluctant to accept Chittenden’s recommendation of such diets as representing “physiological economy,” and argued that the almost universal consumption of high protein diets in prosperous countries showed an important relationship that might not become apparent in short-term trials. He replied that his critics were reversing cause and effect; people did not become rich because they ate more protein, but ate meat and other more expensive high protein foods because they had already attained an income sufficient to afford them. Later studies have only confirmed Chittenden’s findings.” (Carpenter)
Protein digestion and interconversion
“Throughout the writings of Voit, Atwater, and Chittenden, there was the unstated assumption that all proteins were of equal quality. Thus, Atwater had no doubt that meat protein in the diet could safely be replaced by the same quantity of protein from beans. With hindsight, this is surprising because Mulder’s hypothesis that all proteins contained the same radical had collapsed, and even the ratio of carbon : nitrogen had been reported to differ between “legumin” extracted from beans and some animal proteins.” (Carpenter)
“For most of the 19th century, even after the breakdown of Mulder’s theory, it had been assumed by workers in nutrition that proteins ingested in foods were absorbed almost intact and then modified in some slight ways, if necessary, to convert them from “fibrin” to “albumin,” for example. However, other workers studying the physiology of digestion first showed the existence of a substance (pepsin), secreted by the stomach wall, that converted proteins into more soluble derivatives. Liebig regarded this as being no more than breaking up aggregations of molecules, allowing them to pass through the gut more easily. A few years later, the pancreas was found to secrete another substance (trypsin) that further broke down the products of treating proteins with pepsin to produce materials that were noncoagulable, diffusible through parchment and included the chemicals tyrosine and leucine. This subject has been thoroughly reviewed, with full references, by Greenstein and Winitz in an easily available volume.” (Carpenter)
“Now, tyrosine and leucine were already known as two of the compounds, first called “amino-bodies” and then “amino acids,” that chemists had obtained by boiling proteins in strong acids. These breakdown products had not been considered of interest to nutritionists because the kind of destruction effected by strong, boiling acids had been assumed to be quite different from what happened under the mild conditions in the gut. However, the discovery of amino acids as products in a biological system was obviously highly relevant, especially because analysts had already reported that proteins appeared to differ in the relative quantities of different amino acids that they yielded on treatment with acids.” (Carpenter)
“There always seems to be a way around unwelcome findings and in 1895 Chittenden wrote: “We may well consider the formation of these amino acids in pancreatic proteolysis as a means of quickly ridding the body of any excess of ingested protein food, with the least possible expenditure of energy on the part of the system”. Thus, he was suggesting that the proteins that the body needed were still being absorbed pretty well intact, and it was just the unwanted surplus that was being broken down before its disposal. Even in 1902, a German textbook was saying essentially the same thing: “such a profound decomposition would be a waste of chemical potential energy, and a reunion of such products is highly improbable”.” (Carpenter)
“However, other workers in Germany and Denmark were studying whether animals could use mixtures of amino acids as substitutes for dietary protein. Most found that meat proteins treated with pepsin and trypsin for long periods, and apparently free of intact protein, did serve as nutritional substitutes, when fed to adult dogs, but that acid hydrolysates of protein, even after neutralization and removal of excess salts, did not.” (Carpenter)
“It had been suspected that strong acid treatment was destroying some component of the protein because proteins, and even enzymic digests, gave a color reaction suggesting the presence of an indole derivative, but acid hydrolysates did not. Finally, in 1902, F. G. Hopkins and S. W. Cole, working in Cambridge, isolated the amino acid tryptophan, which contains an indole ring, from an enzymic digest and showed that it was destroyed by conditions of acid hydrolysis. Then in 1906, Hopkins and another colleague reported that mice receiving zein (which contains no tryptophan) as their sole protein source, lived longer if they also received a supplement of tryptophan. And in 1909, Abderhalden found that adult dogs could remain in nitrogen balance if the acid-hydrolysates of protein that they were receiving were supplemented with this amino acid. These results did not yet prove that tryptophan was utilized for protein synthesis because there was no growth, but they did show that this organic compound had some essential function.” (Carpenter)
Vitamins and Minerals
We skip over Kenneth’s review of the discovery of minerals as nutrient in the diet since it falls outside the scope of our investigation. Save to say that it is an important constituent of ash obtained in meat analysis. He brilliantly deals with the discovery of the value of selenium, chromium, zinc in diet and the bioavailability of minerals.
Amino acid patterns.
Precisely to our point, Kenneth returns to proteins. He writes, “I have not tried to cover work designed to measure the quantitative requirements for individual nutrients; however, protein is not in this category. No two proteins are identical, nor is the mix of proteins from one food identical to that from another. Therefore, the question remained as to how closely the amino acid pattern of our food needed to match that of our body proteins, which in practice related to the extent to which either animal protein or synthetic amino acids were needed to balance vegetable proteins for a diet to be ideal.” (Carpenter)
“Workers hoped to overcome this problem by stating requirements in terms of individual amino acids, but in 1945 it had not been demonstrated that mixtures of amino acids could completely replace protein in the human diet. William Rose and his colleagues at the University of Illinois had been working to resolve this since 1942 and they reported their findings from 1948 to 1955.” (Carpenter)
Rose’s findings of the amino acids needed by the growing rat and the quantities needed for nitrogen balance in young men.
|Amino acids found essential for the growing rat||Daily need of human adults||Subjects tested|
|Total of the upper levels of essential amino acid needs||6.35|
“Additional glycine and urea were added to raise the total nitrogen intake of the men to 10 g/day, equivalent to 62.5 g crude protein. In further trials with double the upper level of each essential amino acid, it was found that nitrogen balance could be maintained if urea was eliminated and the glycine reduced to 6.5 g/d, so that the total nitrogen content of the diet was only 3.85 g, equivalent to 24 g of crude protein.” (Carpenter)
“Arginine can be synthesized by the rat, but not at a sufficiently rapid rate to meet the demands for growth. Its classification, therefore, as essential or non-essential is purely a matter of definition).” (Carpenter)
“They found that young men would remain in nitrogen balance with surprisingly low levels of amino acids (equivalent to only 24 g crude protein) but only with energy intakes higher than were required with equivalent quantities of intact protein. This was disturbing because it was known that increased energy intakes had an effect on the retention of nitrogen. Even though the quantitative requirements had a question mark attached to them, Rose made the point that the list of essential amino acids required by human adults must now be complete because, in the absence of even one, nitrogen balance would not be obtained at any level of intake.” (Carpenter)
The nitrogen balance (g/d) of an experimental subject receiving 10 g nitrogen/d and either 35 or 45 kcal/d of total energy intake.
|Nitrogen source||35 kcal/d1||45 kcal/d|
|Whole casein||+0.14 (7)1 ; +0.46 (5)||+0.63 (5)|
|Acid-hydrolyzed casein + tryptophan||−0.29 (8)||+0.50 (6)|
|Enzymically hydrolyzed casein||−0.09 (6)||—|
|8 essential amino acids + glycine + urea||−0.91 (6)||+0.33 (5)|
Duration of test period (d).
“Elsie Widdowson and Robert McCance took advantage of the unusual situation in Germany after World War II when food rations were severely limited, so that it was ethical to compare the performance of orphanage children receiving different kinds of special supplements. One group of 47 children was provided with all the bread (85% extraction, i.e., brown but not whole wheat) that they could eat, with calcium and vitamin supplements and their small ration of milk that contributed only 8.8 g protein. Another matched group received the same with extra milk providing three times as much animal protein. These treatments continued for 6 mo under careful supervision. The children, averaging age 9–10 y, grew equally well on both diets, even though in one <12% of their energy came from protein and of this only 14% was animal protein (or “first class” according to some writers). It is unfortunate that this important study was published in a series of monographs not available in many academic libraries, although some of the results have been summarized and discussed elsewhere.” (Carpenter)
The performance of orphanage children receiving unrestricted bread and different rations of milk for 6 mo.
|Low milk||Higher milk|
|Protein intake, g/d|
|85% extr. wheat bread||41.0||34.6|
|Other vegetable foods||11.5||11.5|
|Total energy intake, kcal/(kg · d)||66.6||67.0|
|Nitrogen intake, mg/(kg · d)||322||381|
|Weight gain over 6 mo, kg||2.5||2.5|
|N gain, mg/(kg · d)||13.9||13.9|
|Obligatory N loss, mg/(kg · d)||73||73|
|Theoretical N need, mg/(kg · d)||87||87|
|Efficiency required of dietary N, %||27||23|
“These orphanage children were growing both in height and weight at a rate ∼25% above the average for their ages, perhaps as a “catch up” phenomenon. It is notable that this was possible on the low protein diet, in which mixed proteins themselves contained only ∼3.7% lysine, about half the level in our own body proteins. Human growth is extremely slow and the children were estimated to have gained on average only 14 mg N/(kg body wt·d) with an intake of 322 mg/(kg·d).” (Carpenter)
“A group at the Massachusetts Institute of Technology suggested that, although people on relatively low protein intakes were in nitrogen balance, their equilibrium might be at the expense of lower rates of protein turnover and of potential synthesis of antibodies when exposed to infection. This was an important question and by 1985 procedures were being developed for its measurement using turnover and oxidation studies with isotope-labeled amino acids. However, no definitive answer had been obtained and another worker recommended caution in justifying the need for increased protein on the basis of such measurements.” (Carpenter)
“It was also demonstrated that the requirement of growing chicks for the limiting essential amino acid, lysine, was increased from 0.85% of the diet to ∼1.1% when the total level of protein in the diet was raised from 20% to 30%. Alfred Harper and colleagues at Wisconsin then demonstrated that adding a single amino acid at a fairly high level, for example 2% l-histidine to a diet containing 12% casein (plus methionine) that supported rapid weight gains (56 g in 9 d) in young rats, could inhibit their appetite and performance (in this example to 45 g). Attempts have been made to divide effects of this general kind into toxicities, antagonisms and imbalances. However, there was no evidence that they were likely to occur in practice with humans. One possible concern was that high protein Western diets might be causing an acidosis that resulted in a compensating loss of calcium, and thus of bone.” (Carpenter)
The world protein problem.
“The period had begun therefore with studies indicating that the supply of protein, at least for diets based on cereals, was not a problem. Nevertheless, in 1960, a senior nutritionist said, “We have moved from the era of vitamin research to protein research,” and the head of the Nutrition Division of FAO (the Food and Agriculture Organization of the United Nations) wrote that, “deficiency of protein in the diet is the most serious and widespread problem in the world”.” (Carpenter)
“This idea grew from the finding that a serious disease, called “kwashiorkor” in West Africa and recognized by flaky dermatitis, hair changes, edema and apathy, was also common among 1–4-y-old children in other parts of the developing world. It was found to respond to concentrated relatively high protein nutritional supplements such as skim milk powder, and the previous idea that it was an infantile form of pellagra was abandoned because it did not respond to nicotinic acid or other B-vitamins.” (Carpenter)
“Kwashiorkor was also characterized by liver damage and, because cirrhosis of the liver was common among adults in Africa, it was initially suspected at FAO that the African diet remained protein-deficient throughout life, and that the same might be true throughout the developing world. Milk and milk powder was expensive and in short supply, and it was urged that substitutes needed to be developed.” (Carpenter)
“Much work was carried out in areas where the problem existed, for example at the Institute for Nutrition in Central America and Panama, to develop and test cheaper alternatives to milk powder based on locally available cereals and oilseed flours. These could prevent the condition from developing and also cure it, although not quite as quickly as with milk powder. Individual babies could also be deficient in electrolytes and vitamins as well as in protein and energy. Others suggested that essential fatty acids might also be deficient.” (Carpenter)
“In 1968 the United Nations published a paper entitled International Action to Avert the Impending Protein Crisis. By then, several projects had been set up, with substantial funding (some from governments and foundations), to develop processes and machinery in advanced countries for the preparation of stable, solvent-extracted high protein powders from fish [fish protein concentrate (FPC)] and other materials. This was encouraged by enthusiastic international conferences, even though the original idea had been to devise new crops or simple methods of food processing that could be adopted in underdeveloped villages. In addition, even more sophisticated processes were being planned to produce “single cell protein” (SCP) from yeasts, fungi and bacteria, grown on media ranging from molasses waste to petroleum. Doris Calloway drew attention to the poor tolerance and even toxicity of some SCP materials, and that their high content of nucleic acids was also a problem for humans, who metabolize purines only to the relatively insoluble uric acid, so that they were more suited for animal species that do not have this problem.” (Carpenter)
““Hi-tech” projects, which were supposed to be aiding relatively primitive communities, received particularly bitter criticism from the faculty at the London School of Hygiene and Tropical Medicine who referred to “a continuing process of justifying scientific enthusiasms by the drawing of facile and tenuous links between research which is intellectually exciting to the investigator and problems which are of sufficient public concern to make it politically attractive to devote funds to them”. Even in the U.S., where scientists are usually less willing to risk giving offense, the leader of the government-financed FPC project was to say later (in a book worth reading) that, “Much of the motivation for FPC development had little or nothing to do with the ostensible and well-publicized humanitarian goal”.” (Carpenter)
“This is an episode in our history that nutritional scientists would probably like to forget, but one use of history is to learn from our mistakes and to not repeat them. It was brought to an end by the realization that most kwashiorkor victims had been receiving diets that were as deficient in energy as they were in protein, and too bulky for the youngsters to take in sufficient amounts. The general need was to provide more concentrated foods and correct electrolyte deficiencies rather than concentrate just on protein. It was especially difficult to improve diets based on roots such as cassava that were very bulky as well as low in protein. The United Nations Organization, which had previously emphasized its concerns about “a world protein problem,” made no mention of it at its 1974 World Food Conference.” (Carpenter)
“The synthetic production of essential amino acids likely to be first-limiting in Third World diets was also stimulated in the 1960s. Although results with human trials were generally disappointing, these compounds have found practical uses in intensive pig and poultry feeding.” (Carpenter)
“I include the last section for an important reason. The matter of the determination of meat content is not just an academic consideration for the purpose of complying with some arbitrary national legislative requirement. There is an important moral consideration also.” (Carpenter)
With these set of articles and extracts from some of the best sources on earth, a very broad background is set for a detailed evaluation of the Kjeldahl method of nitrogen determination and the Jones factors, commonly used to determine lean meat content. We achieved much more here. We moved protein and its role in human nutrition to the front and central position in terms of meat processing. Bacon and sausages, like all processed meats, are designed as delicacies for the wealthy. There is no question about this. It is, however, also the staple of the poor and the challenge and responsibility of the meat processor who targets these markets are to provide protein sources that are both delicious and affordable so that every person on earth can enjoy it and derive maximum nutrition from it. As a personal rule of thumb. Myself and my son, determined not to produce something that we are not prepared to eat ourselves or give to our family in the same quantities that clients are likely to consume it.
For part 5, click on
Counting Nitrogen Atoms – The History of Determining Total Meat Content (Part 5):
Carpenter, K. J.; A Short History of Nutritional Science: Part 1, 2, 3, 4, which appeared in The Journal of Nutrition. The links to the four articles are given below.
Russell, R. M., and Scrimshaw, N. S.. 2014. Hamish N. Munro 1915–1994 Biographical Memoires.