Soy protein

Soy proteinis aproteinthat is isolated fromsoybean. It is made fromsoybean mealthat has beendehulledanddefatted. Dehulled and defatted soybeans are processed into three kinds of high protein commercial products:soy flour, concentrates, and isolates. Soy protein isolate has been used since 1959 in foods for its functional properties.
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. Soybeans contain a small but newly very significant 2SAlbuminstorage protein.Legume proteins, such as soy andpulses, belong to theglobulinfamily of seed storage proteins calledleguminandvicilins, or in the case of soybeans,glycininand beta-conglycinin. Soybeans also contain biologically active or metabolic proteins, such as enzymes,trypsininhibitors,hemagglutinins, andcysteine proteasesvery similar topapain. The soycotyledonstorage proteins, important for human nutrition, can be extracted most efficiently by water, water plus dilute alkali (pH7–9), or aqueous solutions ofsodium chloride(0.5–2M≈ 30-120 g/L) from dehulled and defatted soybeans that have undergone only a minimal heat treatment so the protein is close to being native or undenatured.
Soy protein has been available since 1936 for its functional properties. In that year, organic chemistPercy Lavon Juliandesigned 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'sRobert Boyerand Frank Calvert spun into an artificial silk that was then tailored into that now famous "silk is soy" suit thatHenry Fordwore on special occasions. The plant's eventual daily output of 40 tons of soy protein isolate made the Soya Products Division intoGlidden's most profitable division.
At the start ofWorld War II, Glidden sent a sample of Julian's isolated soy (alpha) protein to National Foam System Inc. (today a unit ofKidde Fire Fighting) which used it to develop Aero-Foam,used by theUnited States Navyfor 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 thefire fighting foampossible. When ahydrolysateof 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 SoyaofFort Wayne, Indiana, acquired Julian's Soy Products Division (Chemurgy) of theGliddenPaint Company, Chicago. Central Soya'sBungeProtein Division, in January 2003, joined/merged withDuPont's soy protein businessSolae, which in 1997 had acquiredRalston Purina's soy division, Protein Technologies International (PTI) in St. Louis. On May 1, 2012DuPontannounced its complete acquisition ofSolaefrom 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.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 is used in various foods, such assalad dressings,soups,meat analogues, beverage powders,cheeses,nondairy creamer, frozen desserts,whipped topping,infant formulas,breads,breakfast cereals,pastas, and pet foods.
Soy flour or defatted soy flour (50% protein) glue which originally replaced the more expensivecaseinglue forDouglas firplywoodis re-emerging as the glue of choice to replace toxicurea formaldehydeandphenol formaldehyde resinglues with aformaldehyde-free soy glue.Soy protein is used foremulsificationand texturizing. Specific applications includeadhesives,asphalts,resins, cleaning materials,cosmetics,inks,pleather,paints, paper coatings,pesticides/fungicides,plastics,polyesters, andtextilefibres.
Edible soy protein "isolate" is derived from defatted soy flour with a high solubility in water, as measured by thenitrogen solubility index(NSI). The aqueous extraction is carried out at apHbelow 9. The extract is clarified to remove the insoluble material and thesupernatantliquid is acidified to a pH range of 4-5. The precipitated protein-curd is collected and separated from the whey bycentrifuge. The curd is usually neutralized withalkalito form the sodium proteinatesaltbefore drying
Soy protein concentrate is produced by immobilizing the soy globulinproteinswhile allowing the solublecarbohydrates, soy whey proteins, and salts to be leached from the defatted flakes orflour. The protein is retained by one or more of several treatments: leaching with 20-80%aqueousalcohol/solvent, leaching with aqueousacidsin 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% crudefiber), 6%ashand about 1% oil, but the solubility may differ. Onetonneof defatted soybean flakes will yield about 750 kg of soybean protein concentrate.
Processed soy protein appears in foods mainly in three forms; soy flour, soy protein isolates, and soy protein concentrates.
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 defattedsoy flourwhich has had most of the nonprotein components,fatsand carbohydrates removed. Because of this, it has a neutralflavorand will cause lessflatulencethan soy flours.
Soy isolates are mainly used to improve thetextureof meat products, but are also used to increase protein content, to enhance moisture retention, and as anemulsifier.
Pure soy protein isolate is used mainly by thefood industry. It is sometimes available in health stores or in thepharmacysection of thesupermarket. It is usually found combined with other foodingredients.
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 inpet foods, milk replacements for babies (human andlivestock), and even used for some nonfood applications.
Soy flour is made by grinding (usually cooked) soybeans into a fine powder. It comes in three forms: whole or full-fat (contains naturaloils); defatted (oils removed, made frompress cake) with 50% protein content and with either high water solubility or low water solubility; and lecithinated (lecithinadded to defatted flour). A history of soy flour and grits has been published.As soy flour isgluten-free,yeast-raisedbreadsmade 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.
Kinakois a roasted whole soy flour used inJapanese cuisine. The earliest known reference to kinako dates from 1540 CE. A history of kinako has been published.
Soybean protein is acomplete proteinsince it provides all of theessential amino acidsfor human nutrition.Soybean protein is essentially identical to that of otherlegumepulses(that is to say, legume proteins in general consist of 7S and11S storage proteins), and is one of the least expensive sources of dietary protein.For this reason, soy is important to manyvegetariansandvegans.
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%.Some studies on rats have indicated the biological value of soy protein isolates is comparable to animal proteins such ascaseinif enriched with the sulfur-containing amino acid methionine.
When measuring the nutritional value of protein, the originalprotein efficiency ratio(PER) method, first proposed byThomas Burr OsborneandLafayette Mendelin 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 Universityand theNational Academy of Scienceswhen judging the quality of protein is theprotein 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.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.
Another measure of a protein's use in nutrition is thebiological valuescale, 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.Whole soybean has a biological value of 96, and soy milk 91.
A meta-analysis concluded soy protein iscorrelatedwith significant decreases inserumcholesterol,low density lipoprotein(LDL) cholesterol andtriglycerideconcentrations.High density lipoprotein(HDL) cholesterol did not change. Although there is onlypreclinicalevidence for a possible mechanism, the meta-analysis report stated that soyphytoestrogens– theisoflavones,genisteinanddaidzein– may be involved in reducing serum cholesterol levels.
In 1999, the USFDAgranted 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, theEuropean 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 rejectedhealth claimsthat 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.
Soy protein is generally regarded as storedproteinheld 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 seedgerminates, the protein will be digested, and the released amino acids will be transported to locations of seedling growth.Legumeproteins, such as soy andpulses, belong to theglobulinfamily of seed storage proteins calledlegumin(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 calledglutenor "prolamines".Edestin, a legumin class reserve protein fromhempseeds have six identical subunits. There is one hexameric protein in the rhombohedral unit cell.
Soybeans also contain biologically active or metabolic proteins, such as enzymes,trypsin inhibitors, hemagglutinins, and cysteine proteases very similar topapain. The soycotyledonstorage 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, ahexamer), it must undergo a very limited proteolysisin a manner similar to the cleavage of apeptidefromproinsulinto obtain activeinsulin.
Textured soy protein (TSP) is made by forming a dough from highly soluble (high NSI) defatted soy flour with water in a screw-typeextruder, 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 orsupplement. The extrusiontechnologychanges the structure of the soy protein, resulting in a fibrous, spongy matrix similar in texture to meat.
While TSP has ashelf lifeof more than a year when stored dry atroom temperature, it should be used at once or stored for no more than three days in therefrigeratorafter rehydration. It is usually rehydrated with cold or hot water, but a bit ofvinegarorlemon juicecan be added to quicken the process.
Soy protein products such as TSP are used as low-cost substitutes in meat andpoultryproducts.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 substitutetextured vegetable proteinhas been used for more than 50 years as a way of inexpensively and safely extending ground beef up to 30% forhamburgers, without reducing its nutritional value.