Soya: Review of Health Concerns and Applications in the Meat Industry
By: Eben van Tonder
20 Jan 2019
Introduction
Many popular articles state that soya, in its raw form is poisonous to people. I have always thought that in order for it to be fit for human consumption, one must heat it up to at least 80 deg C. A producer of soya products for the food industry told me, no to long ago, that they heat soya up to 155 deg C during processing in order to destroy all anti-nutritional enzymes.
I was wondering about the use of soy in antiquity because heating soy to 155deg C would have required the right container and a lot of fuel. Was this the way that soy was prepared for millennia for human consumption? If not, is the very high processing parameters really necessary. What is does the latest research tell us about the toxicity of soy?
Vagadia et al. (2015) state that soya “contains a variety of bioactive anti-nutritional compounds including protease (also called a peptidase or proteinase, an enzyme that catalyzes (increases the rate of) proteolysis, the breakdown of proteins into smaller polypeptides or single amino acids; by cleaving the peptide bonds within proteins by hydrolysis, a reaction where water breaks bonds) 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.”
In this introductory article on the subject I start interrogating these matters. Is the processing technology used in many parts of the world not reflective of the prevailing scientific understanding of soy at the time it was invented and popularized? I have seen, many times over, that current science does not always line up with scientific consensus of ages past. Records of modern science are, after all, replete with accounts where, over time, firmly held beliefs were proved wrong and ancient practices and beliefs that were ridiculed, were actually proven right. At the very least, I believe it is justified to ask questions about the modern processing of soy.
Historically Valued Plant
The consideration of modern soy processing, starts in the past. Here I endeavor to look at how old soy is as a stable food and to introduce us to some of the processing methods used. I do a review of some of the modern processing methods in Soya – Its production, Processing and the Danger of Over-Processin, where I also deal with some of the inherent dangers of over-processing it.
“The earliest document with an illustration of the soybean is probably the illustrated Hsin Hsiu Pên Ts’ao (Newly Improved Pharmacopoeia) (659 CE). Illustrations to this work are now lost, but some are preserved in the T’u Ching Pên Ts’ao of 1061 CE and later in the Ch’ung Hsiu Cheng-Ho ChingShih Cheng-Lei Pei-Yung Pên Ts’ao, generally known as
Cheng Lei Pên Ts’ao (CLPT), 249 CE (final version), which remains available today. The entry on soybean (Dadou) in the CLPT includes a picture of the plant. A copy is attached.” Letter from Dr. H.T. Huang, expert on the history of Chinese food and agriculture. 1996. Sept. 29. (Shurtleff, 2014)
An analysis of the earliest references to soy preparations reveals that our current processing methods mimic ancient practices in terms of its broad categories. I share some relevant and interesting dates from Shurtleff (2014). The fact that there are broad similarities between our use of soy and past processing methods does not mean that there is agreement on the particulars of the processing methods. This consideration will be for another time, but as an introduction, looking at the past already inspired us to some exciting possibilities.
Domestication and Boiling in Water
Soy has been used as a food source probably since humans first set eye on the wild soybean plant in China, the home of the soybean. “It was domesticated in the eastern half of north China around the 11th century BCE (Hymowitz 1970, p. 417). More precisely, it probably originated in Liaoning province because the wild soybean grows everywhere and the stages of evolution are apparent (Fehr 1980, p. 3-4)” (Shurtleff, 2014)
“1024 BCE – The ancient character for soybean (shu) appears on four early Zhou dynasty bronze vessels, indicating that the soybean plant was already of some importance by this time (Hu Daojing 1963).” (Shurtleff, 2014)
Roasting
“300 BCE – The words dou and (by inference) dadou are first used to refer to soybeans, and the term daxiaodou is first used to refer to “soybeans and azuki beans” (Rites of the Zhou Dynasty; Zhouli). Increasingly soybeans and azuki beans are mentioned as a pair. This is the also earliest document seen that uses the word qu (“mold ferment,” called koji in Japanese) – but it does not describe what it is or how it is made. The invention of qu is a milestone in Chinese food technology, for it provides the conceptual framework for the three major soyfood fermentations: jiang / miso, soy sauce, and fermented black soybeans (shih). This may be the earliest document seen that mentions roasted soy fl our (douxie).” (Shurtleff, 2014)
The Leaves was used in Food as well as the Bean
“240 BCE – The Book of Master Xun (Xunzi). Master Xun was a philosopher and this is a very well-known work. Chapter 4 mentions soybean leaves (shuhuo).” (Shurtleff, 2014)
In an evaluation of new processing technology and ingredients for the production of hybrid sausages with meat, the use of the soy leaves, therefore, emerges as an ancient contender for inclusion.
Dried and Cooked
“220 BCE – The Record of the Warring States Period (Zhanguoce) states: In the kingdom of Han [near today’s Korea]… The five grains (wugu) are grown. They do not grow wheat; they grow dou (soybeans). The people eat mostly whole dry soybeans cooked into granules like cereal grains (doufan) and soybean leaves in a soup (huogeng). Cooked like cereal grains (doufan), soybeans are said to be quite hard and difficult to digest.” (Shurtleff, 2014)
Fermented
“90 BCE – Records of the Historian (Shiji) by Sima Qian mentions that soybeans (shu) were transported [as a commodity] and that soup was made from soybean leaves (huo). Chapter 69, titled “Economic affairs” (Huozhi liezhuan, a famous chapter) refers to one thousand earthenware vessels of mold-fermented cereal grains and salty fermented soybeans (fermented black soybeans) (niequ yanshi qianhe) as articles of commerce. Soybeans and fermented black soybeans have now clearly become major commodities in the Chinese economy.” (Shurtleff, 2014)
Milled into Flour
“Before and during the Han dynasty (202 BC–220 AD), wheat and soybeans were often mentioned together as inferior or undesirable foods. But when the hand-turned stone mill was introduced (shortly before the Han dynasty), Chinese learned to grind hard-to-cook wheat into flour. This transformed wheat into a very desirable, superior grain whose flour could be used to make a variety of delicious breads, steamed buns, noodles, etc. This development took place during the Han dynasty. When Chinese stopped trying to cook soybeans like cereal grains (fan) or congee / gruel (zhou) or other beans and instead started to experiment to find other ways to transform them into entirely new foods, they first began to realize the great potential of the soybean as a condiment and a protein-rich food. Using fermentation, early Chinese developed fermented black soybeans (chi), fermented soybean paste (jiang), soy sauce, fermented tofu, etc. By sprouting they made soy sprouts for use as a medicine or food. By grinding they created soymilk, yuba, and tofu. These developments were well underway during the Han dynasty, but they continued into the 10th century with the creation of tofu and of soybean oil and cake, into the 16th century with yuba, and on to the 20th century with the concoction of such condiments as black bean sauce, hoisin sauce, jiang-based sauces, etc. Only in the form of green vegetable soybeans (maodou) are soybeans still cooked whole.” (Shurtleff, 2014)
It is in an expansion of this grinding technology, invented shortly before the Han dynasty, where there is the first to bring a new method of processing soy to the fore. We are able to either start the process, using raw soy or we can use as starting material, the soy cakes from the 10th century. I am fully convinced of the need to roast (heat treat) soy for animal food, but is this a requirement for human consumption. An initial discussion follows when we consider the health effects on humans. This will ultimately inform our process parameters.
Stems for human food
“510 CE – Informal Records of Famous Physicians (Mingyi Bielu), by Tao Hongjing, a typical pharmacopoeia, is the first to use the term heidadou to refer to black soybeans. They are used to make sprouts (nie). When the sprout is five inches (cun) long, you dry it; it is called “yellow curls” (huangjuan). After you cook it, it can be eaten. It adds: The leaves can be used to feed livestock. The pods can be used to feed cattle and horses. The stems can be used as fuel to cook food.” (Shurtleff, 2014)
Soy as a Meat Replacer
“965 CE – Anecdotes, Simple and Exotic (Qing Yilu), by Tao Ku is the earliest known document to mention tofu, which it calls doufu. This is the earliest document seen that advocates both vegetarianism and soyfoods, and that recommends the use of soyfoods (tofu) as a replacement for meat.” (Shurtleff, 2014)
Late Reference to Oil Extraction
“980 CE – Treatise on the Mutual Responses of Things According to Their Categories (Wulei Xianggan Zhi) by Lu Zanning (Se Shi) is the earliest document seen that mentions soybean oil or fried tofu. It states: Soybean oil can be mixed with tung oil for use in caulking boats / ships. It also states that frying tofu in soybean oil produces a flavorful dish. Even though soybean cake / beancake is not mentioned, it must have existed in China by this time since it is always a by-product or co-product of the process for making soybean oil.” (Shurtleff, 2014)
It is interesting that soy has been used for almost 2000 years in its cultivated form before mention is made of oil extraction.
Roasted Soy Flour
“1061 – Illustrated Pharmacopoeia: Or, Illustrated Treatise of Pharmaceutical Natural History (Bencao Tujing), by Su Song et al. contains a wealth of information about soybeans and soyfoods. This may be the earliest document seen that mentions roasted soy flour (tangmo).” (Shurtleff, 2014)
The same is true for roasted flour as with oil. It has existed for almost 2000 years as an important food source before roasting the flour is mentioned.
The use of the Entire Plant
“1406 – Treatise on Wild Food Plants for Use in Emergencies (Jiuhuang Bencao), by Zhu Xiao. The most famous “famine herbal,” it described unusual ways of using every part of the soybean plant as human food in times of hunger.” (Shurtleff, 2014)
This fits perfectly into our “root-to-tip” philosophy of using every bit of the plant for food. Its use in the context of drought or famine points to the fact that not every aspect of the plant would be on the same level organileptically, but it is possible to use the entire plant. If we have the technology to process the entire plant in all its aspects into food, in a way that is organoleptically acceptable, it will merely represent a progression of an idea that existed from as early as 1406, and possibly centuries older.
Press-cake and dietary Fibre
“1621 – The Assembly of Perfumes, or Monographs on Cultivated Plants (Qunfang Pu), by Wang Xiangjin is the earliest document seen concerning the use of soybean presscake (zhi or cake or beancake – the residue from pressing out soy oil) as a fertilizer, and the earliest document seen that mentions okara, the residue of dietary fibre that is a by-product of making soymilk or tofu, which it calls zhi (meaning “residue”), and the earliest document seen concerning the use of okara (residue) as a feed for pigs or other animals. In times of famine, people also eat this okara.” (Shurtleff, 2014)
Koji-making
“1637 – Exploitation of the Works of Nature (Tiangong Kaiwu), by Song Yingxing is a very important book, containing many illustrations, showing the advanced state of Chinese technology. It is the earliest document seen that describes the feeding of defatted soybean cakes to livestock – in this case, pigs. It contains the earliest illustrations seen that show clearly the koji-making process for regular or red koji.” (Shurtleff, 2014)
Soy has not only been a super-food for centuries, but its use in medicine is well documented.
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).
Without doing a blow for blow comparison of the ancient processing techniques listed above, one thing is for certain and that is that every soy ingested as a regular food by ancient Chinese were not heated to 155 deg C as is done in some of today’s processes. Reviewing the historical data made me very suspicious about the claims of the toxicity of this plant for humans.
We return to the statement of Vagadia et al. (2015) 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.” Let’s now examine the claim that “inactivation of these trypsin inhibitors, along with deleterious enzymes, microbes, bioactive component.. is crucial”.
Do we have to increase the protein quality by improving its texture, colour, flavour, functionality and digestibility and are these the most important factors to be considered in the crucial stage in the manufacturing of soy products?
Anti-nutritional properties of soybean
“In their natural form, soybeans contain anti-nutrients or phytochemicals which bear toxic effects when ingested by both humans and monogastric food animals. These anti-nutrients are nature’s means of protection for the soybean plant from invasion by animals, bacteria, viruses and even fungi in the ecosystem. The major anti-nutrients in soybean are phytates, protease enzyme inhibitors, soyin, goitrogens, hemagglutinins or lectins, giotrogens, cyanogens, saponins, estrogens, antigens, non-starch polysaccharides and soy oligosaccharide.” (Samuel, 2013)
We start by considering the inactivation of the trypsin inhibitors.
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. Flavin (1982) concludes in a review article that “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. 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)
Ample evidence points to at least one possible health benefit of protease inhibitors. Das and Mukhopadhyay (1994) refer to Kennedy and Troll & Kennedy who discussed the possible role of protease inhibitors in cancer prevention at length. In their 1994 review article, Protease Inhibitors in Chemoprevention of Cancer, Das and Mukhopadhyay (1994) state that the “consumption of soybeans, known to be a rich source of protease inhibitors, has been associated with a decreased incidence of pancreatic cancer in the human population. They also make the excellent point that rice, maize, beans, bread and cereals, all are good sources of protease inhibitors and in the case of rice, maize and beans, reduce the incidence of prostate, colon and breast cancers. In the case of bread and cereals, these have been shown to lower the incidence of oral and pharyngeal cancers among women. (Das & Mukhopadhyay, 1994)
“Of particular interest to us is the detailed review they do on protease inhibitors in soya. They state that “seeds of many leguminous plants, particularly soyabeans and peanuts, are rich sources of protease inhibitors. Soyabean is known to contain at least five protease inhibitors and diets containing soyabeans were shown to inhibit the appearance of tumours in mouse skin treated with nitroquinoline oxide and phorbol myristate acetate, to inhibit formation of breast tumour in Sprague Dawley rats subjected to ionizing radiation and to reduce incidence of spontaneous liver cancer in C, H mice. Feeding of soyabean extracts containing Bowman Birk inhibitor (BBI) was found to suppress dimethylhydrazine-induced colon carcinogenesis in mice. Protective effect of soyabean feeding on experimental carcinogenesis in liver and bladder in mice with nitrite and dibutylamine was reported by Mokhtar et al. and Fitzsimons et al.. A similar observation on the effect of dietary soyasauce was also made in forestomach of mice. Nagao et al. observed that oral administration of nitrite with soyasauce failed to induce cancers in stomach or intestine in Fisher 344 rats. Other studies have revealed that soyabeans can inhibit mammary tumours and that miso, a soyabean paste, can reduce the incidence of DMBA induced mammary adenocarcinoma in rats. Dietary soyabean isolate, low in methionine content, significantly repressed mammary tumour progression in Sprague Dawley rats induced by nitrosomethyl urea. Our studies on the murine system have revealed
that feeding of raw water soaked soyabean was effective in reducing the incidence and growth of leukaernias and lymphomas in experimental animals. An autoclave resistant factor in soyabeans was found to be capable of reducing metastasis of radiation induced lymphosarcoma in mice.” (Das & Mukhopadhyay, 1994)
“While most of these reports have suggested a role for soyabean and soyaproducts in reducing risk of carcinogenesis and reduction in tumour growth, contradictory reports also exist. The potential toxic effects of protease inhibitors which could lead to loss of body weight and produce other associated problems have been a matter of concern to many authors. Kimura et al. noted that diet containing defatted soyabean could induce malignant tumours of the thyroid in iodine-deficient condition. It was also observed by Mc Guinness et al. that a diet of raw soyaflour (containing trypsin inhibitor) increased the DNA, RNA and protein content and weight of pancreas in rats and long-term feeding with the same diet resulted in development of adenocarcinomas and carcinomas of acinar pancreas. Soyabean trypsin inhibitor concentrate was found to enhance the carcinogenicity of azaserine in rat pancreas, but the inhibitor alone did not appear to initiate pancreatic lesions. Hasdai & Liener also concluded from their investigation that raw soyaflour itself has no carcinogenic effect on mouse pancreas and Gumbmann and his group found that while short-term feeding with soya and potato trypsin inhibitor produced hypertrophic and hyperplastic response in the pancreas, the animals were resistant to formation of these lesions after long-term feeding. Moreover, it was felt that humans and mice were not expected to be affected adversely as human trypsin is not strongly inhibited by soyabean trypsin inhibitor. Messadi et al. compared the effect of BBI and trypsin inhibitor (TI) on DMBA induced oral carcinogenesis in hamster cheek pouches and found significant reduction in the number of invasive carcinomas, total number of tumours and turnour mass with BBI but not with TI. Suppression of DMH-induced carcinogenesis by BBI in liver and gastrointestinal tract of mice was noted by St Clair et al. and Billings et al.. N-nitrosornethylbenzylamine-induced oesophageal turnorigenesis was also found to be inhibited by BBI. (Das & Mukhopadhyay, 1994)
They conclude that “protease inhibitors are found to occur naturally in a
variety of leguminous plants as well as in other grains and cereals. Their biological role is not clear, but their function is, in the main, to prevent proteolysis which could results in injury. While protease inhibitors presumably protect plants from the attack of insects and herbivores, epidemiological data implicate an anticarcinogenic property of these agents in humans.” (Das & Mukhopadhyay, 1994)
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:
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 the absorption of iron and zinc, and to 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
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 possibly one very good reason to cook soya well before it is consumed. Lets look at it and determine if it is a real concern.
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. 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 colleagues 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 (the structure that lifts and pulls the cotyledons up through the soil surface; upon germination of the soyabean seed, the hypocotyl elongates, pulling the two cotyledons (seed leaves) above the soil surface with the growing point at at the top of the hypocotyl where the two seed leaves are attached), 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. What happened in Israel, as around the world, is nothing more than the propagation of technology invented in the USA, decades earlier which themselves was a reflection of the prevailing scientific consensus of the time related to the health risks of soya. In itself, it bore little resemblance to age-old processing techniques in the East apart from broad similarities.
“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
Conclusion
Soya is a tremendous food and protein source. The health concerns that existed when processing techniques were invented are reflected in the equipment and process design at that time. What we have around the world is a reflection of the available date and therefore the concerns of the 1940s, ’50s, ’60s and ’70s. I believe it is time for a rethink of our processes. As far as its toxicity for humans is concerned, evidence points to the fact that it is not toxic for humans which is consistent with its wide use in China before more sophisticated processing techniques were invented. It seems as if the entire plant can be used. Before this conclusion can be reached, more investigation is required.
Reference
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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.
Das, S and Mukhopadhyay. 1994. Protease in Chemoprevention in Cancer.
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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 http://dx.doi.org/10.5772/54545
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, https://thesoynutritioninstitute.com
Perkins, S. 2018. What Happens if You Eat Raw Soybeans?
Samuel N. Nahashon and Agnes K. Kilonzo-Nthenge (February 20th 2013). Soybean in Monogastric Nutrition: Modifications to Add Value and Disease Prevention Properties, Soybean – Bio-Active Compounds, Hany A. El-Shemy, IntechOpen, DOI: 10.5772/52991. Available from: https://www.intechopen.com/books/soybean-bio-active-compounds/soybean-in-monogastric-nutrition-modifications-to-add-value-and-disease-prevention-properties
Shurtleff, W., Huang, H.T. & Aoyagi, A. 2014. History of Soybeans and Soyfood in China and Taiwan, and in Chinese Cookbooks, Restaurants, and Chinese Work With Soyfoods Outside China (1024 BCE to 2014): Extensively Annoted Bibliography and Sourcebook Including Manchuria, Hong Kong and Tibet. See also:Li Yu-ying (Li Shizeng) – History of His Work with Soyfoods and Soybeans in France, and His Political Career in China and Taiwan (1881-1973) Soyinfo Centre.
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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