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Soy protein is a protein that is isolated from soybean. It is made from soybean meal that has been husk and defatting. Dehulled and defatted soybeans are processed into three kinds of high protein commercial products: soy flour, , and protein isolate, which is used in food and industrial manufacturing.
Soy protein is generally regarded as being concentrated in protein bodies, which are estimated to contain at least 60–70% of the total soybean protein. Upon germination of the soybean, the protein will be digested, and the released amino acids will be transported to locations of seedling growth.
Legume proteins, such as soy and pulses, belong to the globulin family of seed storage proteins called legumin and , or in the case of soybeans, glycinin and beta-conglycinin. Soybeans also contain biologically active or metabolic proteins, such as enzymes, trypsin inhibitors, , and cysteine proteases similar to papain. The soy cotyledon storage proteins, important for human nutrition, can be extracted most efficiently by water, water plus dilute alkali, or aqueous solutions of sodium chloride from dehulled and defatted soybeans that have undergone only a minimal heat treatment so the protein is close to being native or undenatured.
At the start of World War II, Glidden sent a sample of Julian's isolated soy (alpha) protein to National Foam System Inc. (today a unit of Kidde) which used it to develop Aero-Foam, used by the United States Navy for firefighting and referred to as "bean soup". While not exactly the brainchild of Dr. Julian, it was the meticulous care given to the preparation of the soy protein that made the fire fighting foam possible. When a hydrolysis of isolated soy protein was fed into a water stream, the mixture was converted into a foam by means of an aerating nozzle. The soy protein foam was used to smother oil and gasoline fires aboard ships, and was particularly useful on aircraft carriers. It saved the lives of thousands of sailors.
In 1958, Central Soya of Fort Wayne, Indiana, acquired Julian's Soy Products Division (Chemurgy) of the Glidden Paint Company, Chicago. Central Soya's Bunge Limited Protein Division, in January 2003, joined/merged with DuPont's soy protein business Solae, which in 1997 had acquired Ralston Purina's soy division, Protein Technologies International (PTI) in St. Louis. On May 1, 2012 DuPont announced its complete acquisition of Solae from Bunge.
Food-grade soy protein isolate first became available on October 2, 1959 with the dedication of Central Soya's edible soy isolate, Promine D, production facility on the Glidden Company industrial site in Chicago.William Shurtleff, Akiko Aoyagi History of Cooperative Soybean Processing in the United States: Extensively Annotated Bibliography and Sourcebook Soyinfo Center, 2008 An edible soy isolate and edible spun soy fiber have also been available since 1960 from the Ralston Purina Company in St. Louis, who had hired Boyer and Calvert. In 1988, PTI became the world's leading maker of isolated soy protein.
Soy protein concentrate is produced by immobilizing the soy globulin proteins while allowing the soluble carbohydrates, soy whey proteins, and salts to be leached from the defatted flakes or flour. The protein is retained by one or more of several treatments: leaching with 20-80% aqueous ethanol/solvent, leaching with aqueous acids in the isoelectric zone of minimum protein solubility, pH 4-5; leaching with chilled water (which may involve calcium or magnesium cations), and leaching with hot water of heat-treated defatted soy meal/flour.
All of these processes result in a product that is 70% protein, 20% carbohydrates (2.7 to 5% crude fiber), 6% ash and about 1% oil, but the solubility may differ. One tonne of defatted soybean flakes will yield about 750 kg of soybean protein concentrate.
Soy isolates are mainly used to improve the texture of meat products, but are also used to increase protein content, to enhance moisture retention, and as an emulsifier.
Pure soy protein isolate is used mainly by the food industry. It is sometimes available in health stores or in the pharmacy section of the supermarket. It is usually found combined with other food .
Soy protein concentrate retains most of the fiber of the original soybean. It is widely used as functional or nutritional ingredient in a wide variety of food products, mainly in baked foods, breakfast cereals, and in some meat products. Soy protein concentrate is used in meat and poultry products to increase water and fat retention and to improve nutritional values (more protein, less fat).
Soy protein concentrates are available in different forms: granules, flour and spray-dried. Because they are very digestible, they are well-suited for children, pregnant and lactating women, and the elderly. They are also used in , milk replacements for babies (human and livestock), and even used for some nonfood applications.
Soy grits are similar to soy flour except the soybeans have been toasted and cracked into coarse pieces.
Kinako is a roasted whole soy flour used in Japanese cuisine. The earliest known reference to kinako dates from 1540 CE. A history of kinako has been published.Shurtleff, W.; Aoyagi. A.. 2012. "History of Roasted Whole Soy Flour (Kinako), Soy Coffee... (1540–2012)." Lafayette, California: Soyinfo Center. 709 pp. (1,420 references; 76 photographs and illustrations, Free online).
Soy flour contains 50% protein.
The digestibility of some soyfoods are as follows; steamed soybeans 65.3%, tofu 92.7%, soy milk 92.6%, and soy protein isolate 93–97%."Nutritional Value of Food Protein Products", I.E. Liener; In Smith and Circle, editors; "Soybeans: Chemistry and Technology." Published by The AVI Publishing Co. 1972. Westport, Connecticut. Some studies on rats have indicated the biological value of soy protein isolates is comparable to animal proteins such as casein if enriched with the sulfur-containing amino acid methionine.Hajos, G., et al., Effects of Proteolytic Modification and Methionine Enrichment On the Nutritional Value of Soya Albumins For Rats. Nutri. Biochem. 7:481-487, 1996.
When measuring the nutritional value of protein, the original protein efficiency ratio (PER) method, first proposed by Thomas Burr Osborne and Lafayette Mendel in 1917, was the most widely used method until 1990. This method was found to be flawed for the biological evaluation of protein quality because the young rats used in the study had higher relative requirements for sulfur-containing amino acids than did humans. As such, the analytical method universally recognized by the FAO/WHO (1990), as well as the FDA, USDA, United Nations University and the National Academy of Sciences when judging the quality of protein is the PDCAAS, as it is viewed as accurately measuring the correct relative nutritional value of animal and vegetable sources of protein in the diet.FAO/WHO (1991) Protein Quality Evaluation Report of Joint FAO/WHO Expert
Consultation, Food and Agriculture Organization of the United Nations, FAO Food
and Nutrition Paper No. 51, Rome.Schaafsma, G. (2000) 'The protein digestibility-corrected amino acid score. Journal of Nutrition 130, 1865S-1867S
Based on this method, soy protein is considered to have a similar equivalent in protein quality to animal proteins. Egg white has a score of 1.00, soy concentrate 0.99, beef 0.92, and isolated soy protein 0.92. In 1990 at an FAO/WHO meeting, it was decided that proteins having values higher than 1.0 would be rounded or "leveled down" to 1.0, as scores above 1.0 are considered to indicate the protein contains essential amino acids in excess of the human requirements.FAO/WHO 1990. Expert consultation on protein quality evaluation. Food and Agriculture Organization of the United Nations, Rome.
In 1999, the US FDA granted a health claim for labeling of manufactured food products containing soy: "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease." In 2019, the FDA reassessed and supported the 1999 health claim by looking at data from 46 randomized controlled trials.
In 2006, an American Heart Association review of soy protein benefits indicated only weak confirmation for the cholesterol-lowering claim about soy protein. The panel also found soy isoflavones do not reduce postmenopause "hot flashes" in women, nor do isoflavones lower risk of cancers of the breast, uterus, or prostate. Among the conclusions, the authors stated, "In contrast, soy products such as tofu, soy butter, soy nuts, or some soy burgers should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat. Using these and other soy foods to replace foods high in animal protein that contain saturated fat and cholesterol may confer benefits to cardiovascular health."
In 2012, the European Food Safety Authority (EFSA) published a scientific opinion on isolated soy proteins and reduction of blood LDL-cholesterol concentrations. EFSA concluded that a cause and effect relationship was not established between the consumption of soy protein and a reduction in blood LDL-cholesterol concentrations. In 2010, the EFSA had already rejected that linked the consumption of soy protein to the maintenance or achievement of a normal body weight, the reduction of blood cholesterol concentrations, or the protection of DNA, proteins and lipids from oxidative damage.
Soybeans also contain biologically active or metabolic proteins, such as enzymes, trypsin inhibitors, hemagglutinins, and cysteine proteases very similar to papain. The soy cotyledon storage proteins, important for human nutrition, can be extracted most efficiently by water, water plus dilute alkali (pH 7–9), or aqueous solutions of sodium chloride (0.5–2 M) from dehulled and defatted soybeans that have undergone only a minimal heat treatment so the protein is close to being native or undenatured. Soybeans are processed into three kinds of modern protein-rich products; soy flour, soy concentrate, and soy isolate.
For the 11S protein, glycinin, to fold properly into its hexagonal shape (containing six subunits, a hexamer), it must undergo a very limited proteolysis in a manner similar to the cleavage of a peptide from proinsulin to obtain active insulin.
While TSP has a shelf life of more than a year when stored dry at room temperature, it should be used at once or stored for no more than three days in the refrigerator after rehydration. It is usually rehydrated with cold or hot water, but a bit of vinegar or lemon juice can be added to quicken the process.
Soy protein products such as TSP are used as low-cost substitutes in meat and poultry products. Food service, retail and institutional (primarily school lunch and correctional) facilities regularly use such "extended" products. Extension may result in diminished flavor, but fat and cholesterol are reduced. Vitamin and mineral fortification can be used to make soy products nutritionally equivalent to animal protein; the protein quality is already roughly equivalent. The soy-based meat substitute textured vegetable protein has been used for more than 50 years as a way of inexpensively and safely extending ground beef up to 30% for hamburgers, without reducing its nutritional value.
Concentrates
Soy protein concentrate is about 70% soy protein and is basically defatted soy flour without the water-soluble carbohydrates. It is made by removing part of the carbohydrates (soluble sugars) from dehulled and defatted soybeans.
Flours
Soy flour is made by grinding (usually cooked) soybeans into a fine powder. It comes in three forms: whole or full-fat (contains natural ); defatted (oils removed, made from press cake) with 50% protein content and with either high water solubility or low water solubility; and lecithinated (lecithin added to defatted flour). A history of soy flour and grits has been published.Shurtleff, W.; Aoyagi. A.. 2013. "History of Soy Flour, Grits and Flakes (510 CE to 2013)." Lafayette, California: Soyinfo Center. 2,053 pp. (6,616 references; 202 photographs and illustrations, Free online). As soy flour is gluten-free, yeast-raised made with soy flour are dense in texture.
Nutrition
Soybean protein is a complete protein since it provides all of the essential amino acids for human nutrition. Soybean protein is essentially identical to that of other legume pulses (legume proteins in general consist of 7S and 11S storage proteins), and is one of the least expensive sources of dietary protein.Derbyshire, E. et al.1976. Review: Legumin and vicilin, storage proteins of legume seeds" Phytochemistry 15:3. For this reason, soy protein is consumed by Vegetarianism and Veganism.
Biological value
Another measure of a protein's use in nutrition is the biological value scale, which dates back to 1911; it relies on nitrogen retention as a measurement of protein quality. Soybean protein isolate has a biological value of 74.Protein Quality-Report of Joint FAO’/WHO Expert Consultation, Food and Agriculture Organisation, Rome, FAO Food and Nutrition Paper 51, 1991. Whole soybean has a biological value of 96, and soy milk 91.Smith, A.K. and Circle, S.J.1972. Soybeans: Chemistry and Technology.Table7.7 page 219. AVI publishing.
Health effects
A meta-analysis concluded soy protein is correlated with significant decreases in blood serum cholesterol, low density lipoprotein (LDL) cholesterol and triglyceride concentrations. High density lipoprotein (HDL) cholesterol did not change. Although there is only preclinical evidence for a possible mechanism, the meta-analysis report stated that soy phytoestrogens – the isoflavones, genistein and daidzein – may be involved in reducing serum cholesterol levels.
Role in the growth of the soybean plant
Soy protein is generally regarded as stored protein held in discrete particles called "protein bodies" estimated to contain at least 60% to 70% of the total protein within the soybean seed. This protein is important to the growth of new soybean plants, and when the soybean seed germination, the protein will be digested, and the released amino acids will be transported to locations of seedling growth. Legume proteins, such as soy and pulses, belong to the globulin family of seed storage proteins called legumin (11S globulin fraction) and vicilins (7S globulin), or in the case of soybeans, glycinin and beta-conglycinin. Grains contain a third type of storage protein called gluten or "prolamines". Edestin, a legumin class reserve protein from hemp seeds have six identical subunits. There is one hexameric protein in the rhombohedral unit cell.
Uses
Textured soy protein
Textured soy protein (TSP) is made by forming a dough from highly soluble (high NSI) defatted soy flour with water in a screw-type Food extrusion, and heating with or without steam. The dough is extruded through a die into various possible shapes: granules, flakes, chunks, goulash, steakettes (schnitzel), etc., and dried in an oven. TSP made from soy flour contains 50% soy protein and must be rehydrated before use at a weight ratio of 1 TSP:2 water. However, TSP, when made from soy concentrate, contains 70% protein and can be rehydrated at a ratio of 1:3. It can be used as a meat replacement or supplement. The extrusion technology changes the structure of the soy protein, resulting in a fibrous, spongy matrix similar in texture to meat.
(1972). 9780870551116, Avi Pub. Co. ISBN 9780870551116
See also
Works cited
(2025). 9789400717633, Springer. ISBN 9789400717633
External links
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