Soy protein is a protein that is isolated from soybean. It is made from soybean meal that has been dehulled and defatted. Dehulled and defatted soybeans are processed into three kinds of high-protein commercial products: soy flour, concentrates, and 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 vicilins, or in the case of soybeans, glycinin and beta-conglycinin. Soybeans also contain biologically active or metabolic proteins, such as enzymes, trypsin inhibitors, hemagglutinins, 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.
History Soy protein has been available since 1936. In that year, organic chemist Percy Lavon Julian designed the world's first plant for the isolation of industrial-grade soy protein called alpha protein. The largest use of industrial-grade protein was, and still is, for paper coatings, in which it serves as a pigment binder. However, Julian's plant must have also been the source of the "soy protein isolate" which Ford's Robert Boyer and Frank Calvert spun into an artificial silk that was then tailored into that now famous "silk is soy" suit that Henry Ford wore on special occasions. The plant's eventual daily output of 40 tons of soy protein isolate made the Soya Products Division into Glidden's most profitable division.
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 Fire Fighting) 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 hydrolysate 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 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.
Food uses Soy protein is used in various foods, such as salad dressings, soups, meat analogues, beverage powders, cheeses, nondairy creamer, frozen desserts, whipped topping, infant formulas, breads, breakfast cereals, pastas, and pet foods.
Manufacturing uses Soy flour or defatted soy flour (50% protein) glue which originally replaced the more expensive casein glue for Douglas fir plywood is a common choice to replace toxic urea formaldehyde and phenol formaldehyde resin glues with a formaldehyde-free soy glue. Soy protein is used for emulsification and texturizing. Specific applications include adhesives, asphalts, resins, cleaning materials, cosmetics, inks, pleather, paints, paper coatings, pesticides and fungicides, plastics, polyesters, and textile fibres.
Production methods Edible soy protein isolate is derived from defatted soy flour with a high solubility in water, as measured by the nitrogen solubility index (NSI). The aqueous extraction is carried out at a pH below 9. The extract is clarified to remove the insoluble material and the supernatant liquid is acidified to a pH range of 4-5. The precipitated protein-curd is collected and separated from the whey by centrifuge. The curd is usually neutralized with alkali to form the sodium proteinate salt before drying.
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 alcohol/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.
Product types
Processed soy protein appears in foods mainly in three forms; soy flour, soy protein isolates, and soy protein concentrates.E.S. Sipos. Edible Uses of Soybean Protein
Isolates Soy protein isolate is a highly refined or purified form of soy protein with a minimum protein content of 90% on a moisture-free basis. It is made from defatted soy flour which has had most of the nonprotein components, fats and carbohydrates removed. Because of this, it has a neutral flavor and will cause less flatulence than soy flours.
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 ingredients.
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.
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 pet foods, milk replacements for babies (human and livestock), and even used for some nonfood applications.
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 oils); 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 breads made with soy flour are dense in texture.
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).
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 vegetarians and vegans.
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 protein digestibility-corrected amino acid score, 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 . Expert consultation on protein quality evaluation. Food and Agriculture Organization of the United Nations, Rome.
Biological value