Soya: Review of some health concerns and applications in the meat industry


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):

“Abortion, ague, alcoholism, anodyne, antidote for aconite or centipede or croton, antivinous, anus, apertif, ascites, ataxia, blindness, bone, bugbite, burn, carminative, chestcold, chill, circulation, cold, complexion, decongestant, diaphoretic, diuretic, dogbite, dysentery, dyspnea, eczema, edema, enuresis, feet, fever, halitosis, headache, hematuria, impotence, intoxication, kidney, labor, laxative, leprosy, malaria, marasmus, marrow, melancholy, metrorrhagia, nausea, nervine, ophthalmia, pile, pregnancy, preventive (abortion) puerperium, refrigerant, resolvent, rheumatism, scald, sedative, skin, smallpox, snakebite, sore, splenitis, splinter, stomach, tinea, venereal, vertigo, vision.”

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.

Trypsin Inhibitors

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

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:

Phytic Acid in food

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.  (

“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.

Lectin Effects

“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)

Further reading

A tremendous resource on research on soya is HISTORY OF SOYBEANS AND SOYFOODS IN THE MIDDLE EAST


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.

Arnarson, A.  2018. Phytic Acid 101: Everything You Need to Know.

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.

Engelking, Larry R. (2015-01-01). Textbook of Veterinary Physiological Chemistry (Third Edition). Boston: Academic Press. pp. 39–44. ISBN 9780123919090.

Flavin DF. The effects of soybean trypsin inhibitors on the pancreas of animals and man: a review. Review article. Vet Hum Toxicol. 1982. 1982 Feb;24(1):25-8.

Groves, M..  2018.  Is Soy Good or Bad for Your Health?

Hassan, S. M..  2013.  Soybean, Nutrition, and Health.  Intech

Kühne, W. 1877. “Über das Trypsin (Enzym des Pankreas)”, Verhandlungen des naturhistorisch-medicinischen Vereins zu Heidelberg, new series, vol. 1, no. 3, pages 194-198

Messina, M.  2018.  Is Soybean Lectin an Issue?  The Soy Nutrition Institute
The latest findings in soy health research,

Perkins, S.  2018. What Happens if You Eat Raw Soybeans?

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

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The Chemistry of Sulfur Dioxide in Boerewors

The Chemistry of Sulfur Dioxide in Boerewors
By Eben van Tonder
15 November 2018


When making boerewors for commercial sale, we add sulfur dioxide as preservative and giving longevity to the product colour.

Spoilage of meat by microorganisms leads to the development of off-flavors, oxidative rancidity, discoloration, gas production and, often, slime formation (LLOYD- PURYEAR et al., 1991; COCOLIN et al., 2004). The reason for fresh sausage being highly perishable are their characteristic pH and aw values. In boerewors the pH is kept low through the addition of vinegar which itself is a string anti-microbial which should aid greatly in preserving the sausage.

It may however not be sufficient and sulfur dioxide is added as an additional hurdle. Along with factory cleaning and maintaining processing temperatures of the meat between 2 and 3 deg C, boerewors should have a good shelf life under chilled conditions and vacuum packed or packed in a foamo tray.

Here we review sulfur dioxide.

Mechanism as antimicrobial

Sulfur dioxide (SO2) is a broad spectrum antimicrobial agent and antioxidant. It has been known since the early 1900 that only the free form of sulfur dioxide (i.e. unbound to another molecule) have any antimicrobial efficacy. In the 1960’s it was shown that molecular SO2 is several hundred times more effective than bisulfite. (Henderson, Pat. 2009)

The antimicrobial mechanism of SO2 is that it enters the microbe and disrupts the activity of the enzymes and proteins of the cell. (Henderson, Pat. 2009)

Only the SO2 molecule can enter through the cell membrane, it is the concentration of SO2 that controls the antimicrobial efficacy. (Henderson, Pat. 2009)

The percentage of SO2 is again in turn dependent on pH. The lower the pH, the greater the percentage of SO2. SO2 readily dissolves in water. The reaction is

H2O + SO2 ↔ H+ + HSO3– ↔ 2H+ + SO3=

SO2 is what we refer to as molecular SO2. The products to the right of the balanced reaction are called the sulfites. HSO3 is called bisulfite and SO3= is called sulfite. “The negative signs (– and =) denote the negative charge of the bisulfite and sulfite ions (molecules with a charge are called ions). The double arrows (↔) of the equation denote that the reaction is at equilibrium.” (Henderson, Pat. 2009)

At equilibrium, the rate at which bisulfite ions become sulfite is the same as the rate at which sulfite ions become bisulfite. The reaction between the different types of sulfite is going both ways at a steady state so the concentration of the sulfite compounds remains steady.” (Henderson, Pat. 2009)

“While the concentration of the different forms of sulfites may be steady, it does not mean there are equal amounts of the compounds in solution; the acidity or pH of the water has a huge effect on their concentration. The more acidic or the lower the pH of the water, the more heavily the reaction is weighted to the molecular SO2 side. The more basic or higher the pH is, the more sulfite is present.” (Henderson, Pat. 2009)

“Sulfites will also react with other chemical constituents found in a meat cure such as sugars, acetaldehyde, and phenolic compounds, added to the meat as liquid smoke or during the smoking process. When a sulfite reacts with another molecule and becomes part of its structure it no longer takes part in the equilibrium reaction and it is called bound. Sulfites that still are part of the equilibrium reaction are called free. The combined amounts of free and bound sulfites are called “total SO2.”” (Henderson, Pat. 2009)

The more compounds that are available in meat and in the meat cure for sulfites to bind to, the higher the ratio of bound to total sulfites there will be. Therefore, smoked sausages that are produced with a sweet cure and where SO2 is relied on for preservation will have a lower ratio of free to total SO2. (Henderson, Pat. 2009)

“Knowing both the amount of free and total sulfites is very important because only the free forms of sulfites are available for providing a preservative role. This is often expressed as ppm free SO2/ppm total SO2 to denote which number is free and which is total; these numbers can readily be determined by chemical analysis.” (Henderson, Pat. 2009)

Effect in Meat Spoilage Organisms

“Some common spoilage organisms are Acetobacter, Lactobacillus, Pediococcus, and Brettanomyces. All of these are sensitive to some degree to sulfur dioxide but the best results come from a combination of sulfur dioxide and good factory hygiene practices.” (Henderson, Pat. 2009)

“Acetobacter is also known as acetic acid or vinegar bacteria. As the name implies, it can grow in meat and produce vinegar (acetic acid). It can be controlled using sulfur dioxide.” (Henderson, Pat. 2009)

If Lactobacillus has already become established, lysozyme (an antimicrobial enzyme that is effective at high pH), can be added to control growth. Pediococcus produces an off-aroma that is described as “vegetal” or “dirty socks” and often comes from equipment and meat working surfaces that have not been kept clean. (Henderson, Pat. 2009)

Mechanism as antioxidant

The role of an antioxidant in the boerewors will be to provide cour stability. Fading of the cour will happen due to oxidation or the action of light.

Although the sulfite ion (SO3=) can bind with oxygen, there is almost no sulfite ion present in solution at the pH range found in boerewors. Rather sulfur dioxide prevents oxidation by binding with the precursors involved in oxidative reactions preventing them from reacting with oxygen or by binding with compounds already oxidized to reverse oxygen’s effect. (Henderson, Pat. 2009)

In fruit juices, sulfur dioxide acts by reducing the activity of the degenerative enzyme tyrosinase (polyphenol oxidase). (Henderson, Pat. 2009)

If colour is the only reason for adding sodium or potassium metabisulfite, I would seriously consider rather using ascorbic acid or erythorbic acid. The latter is a stereoisomer of ascorbic acid and a lot less expensive even though one sacrifice a considerable amount of functionality. It may be easier to work with erythorbic acid. In combination with isocitric acid, these have been proven to be highly effective. Isocitric acid is a structural isomer of citric acid.

I refer to the use of the acids, but of course, the salts may be used with the same results, depending on price and availability. Care must, however, be taken that the pH of the sausage does not drop below 5, to prevent denaturing of the meat proteins.

Mix the ingredients in a solution and determine its pH. Adjust to around 5.7 by using sodium hydroxide or potassium carbonate or sodium hydrogen carbonate or something similar.

The amount of isocitric acid to be added is 0.2 to 20 times the ascorbic or erythorbic acids. Ascorbic or erythorbic acid is normally added at 0.05% of FP.

Such a blend was proposed in 1969 by Nakao, Seishi Takagi, and Hiromi Nakatani on behalf of Takeda Pharmaceutical Co Ltd.

How to add SO2?

“Sulfur dioxide is available in its pure form as a compressed gas that can be made into an aqueous solution. Most processors use a stable, powdered form of sulfur dioxide called potassium metabisulfite or sodium metabisulfite. Potassium metabisulfite has the molecular formula of K2S2O5 and is 57.6% available SO2 by weight. Potassium metabisulfite is usually abbreviated as PMBS or sometimes KMB or KMBS (K is the chemical symbol for potassium).

The molecular formula for sodium metabisulfite is Na2S2O5 and is 66.5% available SO2 by weight. we abbreviate it SMBS.

The formula and calculations for determining how many grams of PMBS you need to add for a given rise in ppm of SO2 are:

final product weight x ppm required /1000 x 0.576 = grams of SMBS to add

The formula for SMBS is:

final product weight x ppm required /1000 x 0.665 = grams of SMBS to add

1000 converts mg/L to g/L.

0.576 and 0.665 are the g’s of SO2 in PMBS and SMBS respectively.

There is a certain amount of guesswork in how much SO2 will be available. Always add a bit more. Many countries around the world, including South Africa, allows 500ppm in the final product. At least 30% of the SO2 from PMBS or SMBS added to meat will be lost immediately. Therefore, aim for 600 ppm inclusion which should get you to the 500 ppm. I suggest 1g to 1.2g per kg FP in sausages.

The differences between PMBS and SMBS are sodium metabisulfite has a molecular weight of 190.1 g/mole. A maximum of 650 g of this chemical can be dissolved in 1 liter of water at 20 degrees Celsius. Potassium metabisulfite has a molecular weight of 222.32 g/mole and is less soluble in water. Only 450 g can be dissolved in 1 liter of water. (Morgan, S. 2017)

Some processors prefer to use a premixed aqueous solution of sulfur dioxide rather than PMBS. The liquid is typically 5% to 10% SO2 by weight and it can be purchased or made up at the processing plant by dissolving SO2 gas or PMBS into distilled water. The liquid can be directly added to meat without mixing and the proper amount is measured volumetrically instead of weighed on a scale.

Measuring Sulfur Dioxide

The exact amount of both free and total sulfur dioxide in meat can only be determined by chemical analysis. Two primary methods that are used are known as the Ripper method and the Aeration-Oxidation method. Both methods have limitations and require an investment in laboratory equipment and chemicals and a degree of expertise in laboratory practices.


Vinegar or acetic acid provides powerful antimicrobial action in boerewors. Adding Sulfur Dioxide will contribute to the overall antimicrobial action and enhance and prolong the fresh meat colour. It will also increase the molecular Sulfur Dioxide in the sausage matrix. Smoking boerewors will reduce this by depleting the molecular Sulfur Dioxide.

Producers must consider adding sulfur dioxide carefully since it is a known allergen. Despite this, it is a very popular chemical to add to fresh sausages. Greater care should be taken with hygiene during production, keeping meat temp < 3 deg C and it should not be necessary to add this. A suggestion that will horrify meat scientists around the world and masters butchers alike is that if there is any doubt about the micro on the meat such as will be the case if mince is used, I would wash the trim first with a 2% acetic acid solution in cold water. Dip it using a clean crate. I would then use sodium ascorbate or erythorbate in conjunction with isocitric acid to address the matter of colour fading.

Overall Boerewors should have a good shelf life.


COCOLIN, L. et al. Study of the ecology of fresh sausages and characterization of populations of lactic acid bacteria by molecular methods. Applied and Environmental Microbiology, v. 70, p. 1883-1894, 2004. PMid:15066777 PMCid:PMC383013. http://

Henderson, Pat. 2009. Science behind this anti-microbial, anti-oxidant, wine additive. Practical Winery & Vineyard Journal. January/ February 2009.

LLOYD-PURYEAR, M. et al. Meningitis caused by Psychrobacter immobilis in an infant. Journal of Clinical and Microbiology, v. 29, p. 2041-2042, 1991. PMid:1774332 PMCid:PMC270256.

Morgan, S. 2017. Sodium Metabisulfite Vs. Potassium Metabisulfite.