Soy protein

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Soy protein is generally regarded as the storage protein held in discrete particles called 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 leguminins (11S) and vicilins (7S), or glycinin and beta-conglycinin in soybeans. Grains contain a third type of storage protein called gluten or "prolamines". Soybeans also contain biologically active or metabolic proteins such as enzymes, trypsin inhibitors, hemagglutinins, and cysteine proteases. 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 that the protein is close to being native or undenatured. Soybeans are processed into three kinds of protein-rich products; soy flour, soy concentrate, and soy isolate.

History

Soy protein {90%protein (N x 6.25) on a moisture-free basis} has been available since 1935 for its functional properties. In 1935, African-American chemist Percy Julian designed the world's first plant for the isolation of industrial-grade soy protein. The largest use of industrial grade protein was and still is for paper coatings, in which it serves as a pigment binder. However, the plant may have also been the source of the artificial silk for the "silk is soy" suit which Henry Ford wore on special occasions.

During WWII, the fire-extinguishing hydrolyzed soy protein foam, "Aero-Foam", was the brainchild of Percy Lavon Julian. The foam -- U.S. Navy's fire-fighting "bean soup" -- could smother oil and gasoline fires on board ships, especially aircraft carriers, before the flames could engulf the ship. It saved the lives of countless American sailors.

Food grade soy protein isolate first became available on October 2 1959. An edible soy isolate and edible spun soy fibre has also been available since 1960.

Recently, soy protein popularity has increased due to its use in health food products.

Food uses

Soy protein is used in a variety of foods such as salad dressings, soups, imitation meats, beverage powders, cheeses, non-dairy creamer, frozen desserts, whipped topping, infant formulas, breads, breakfast cereals, pastas, and pet foods.

Functional uses

Soy protein is used for emulsification and texturizing. Specific applications include adhesives, asphalts, resins, cleaning materials, cosmetics, inks, pleather, paints, paper coatings, pesticides/fungicides, plastics, polyesters and textile fibers.

Production methods

Edible soy protein "isolate" is derived from defatted soy flour with a high solubility in water (high NSI). The aqueous extraction is carried out at a pH below 9. The extract is clarified to remove the insoluble material and the "supernatant" 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 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

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 non-protein components, fats and carbohydrates removed. Because of this, it has a neutral flavor and will cause less gas due to bacterial flatulence.

Soy isolates are mainly used to improve the texture of meat products, but are also used to increase protein content, enhance flavor, and as an emulsification).

Soy protein isolate is used in health foods as it is a complete vegetable protein containing all the essential amino acids. Also, it has a very low fat content when compared to animal sources of protein. It is also claimed that soy protein isolate may reduce the risk of coronary heart disease and help prevent osteoporosis, some cancers and menopausal symptoms. Currently, the FDA is examining health concerns related to levels of the toxin furan in soy protein isolate and other foods.

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 soybean without the water soluble carbohydrates. It is made by removing part of the carbohydrates (sugars) from dehulled and defatted soybeans.

Soy protein concentrate retains most of the fiber of the original soybean. Soy protein concentrate 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 replacers for calves and pigs, and even used for some non-food applications.

Flours

Soy flour, is made by grinding soybeans,into a fine powder. It comes in three forms: natural or full-fat (contains natural oils); defatted (oils removed) with 50% protein content and with either high water solubility or low water solublity; and lecithinated (lecithin added). 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 that the soybeans have been toasted and cracked into coarse pieces.

The nutritional value of soy protein

Soybeans are a source of complete protein. Soybean protein is essentially identical to that of other legume pulse {that is to say legume proteins in general, consist of 7S and 11S storage proteins} vegetable proteins. Additionally, soy protein has the highest yield per square meter of growing area, and is the least expensive source of dietary protein. A complete protein is one that contains significant amounts of all the essential amino acids that must be provided to the human body because of the body's inability to synthesize them. For this reason, soy is important to many vegetarians and vegans. However, the phrase 'complete protein' is not entirely agreed-upon in usage by the scientific community.

The digestibility of some soyfoods are as follows: steamed soybeans 65.3%, tofu 92.7%, soy "milk" 92.6%, soy protein isolate 93–97%. Some studies on rats have indicated that the biological value and digestibility of soy protein isolates is comparable in nutritional value to animal proteins such as casein, particularly when enriched with the sulfur-containing amino acid methionine.

Lafayette B. Mendel and Morris S. Fine of the Sheffield Laboratory of Physiological Chemistry at Yale University made the observation in the September 1911 edition of the Journal of Biological Chemistry that soybeans produce a positive nitrogen (N) balance in a human subject when they conducted a study to determine the utilization of legume proteins. The treatment called for 5 days of a 2400 calorie diet consisting of meat, eggs, nut butter, potatoes and fruit, followed by 6 days where 90.5% of total nitrogen was supplied by soybeans, and then another 5 days of the first diet, minus the nut butter. They discovered that the soy bean nitrogen is "distinctly (if only slightly) less well utilized than that of the preceding and suceeding mixed diets".

When measuring the nutritional value of protein, the original Protein Efficiency Ratio PER method first proposed by Osborne and Mendel in 1917, and the most widely used method, until 1990, for the biological evaluation of protein quality was found to be flawed for humans because the young rats used in the study have higher relative requirements for sulfur-containing amino acids. As such the analytical method that is universally recognized by the FAO/WHO (1990) as well as the FDA, USDA, United Nations University (UNU) and the National Academy of Sciences when judging the quality of protein is 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. 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, beef 0.92, isolated soy protein 0.92, and soy concentrate 0.99. In 1990 at a 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 that the protein contains essential amino acids in excess of the human requirements. The approach of 'capping off' scores at 1.0 as the highest possible rating implies injustice to high-quality proteins which can compensate for low-quality ones by virtue of their high content of essential amino acids. Egg has an actual PDCAA score of 1.19 compared to 0.92 for isolated soy protein, however when leveled down, they appear much closer.

Biological value of soy protein

Further information: ]

Another measure of a protein's use in nutrition is the Biological Value scale. The Biological Value method, which dates back to 1911 relies on nitrogen retention as an indicator of protein quality.

According to the 1972 publication Soybeans: Chemistry and Technology, highly refined isolated soy protein has an average biological value of 71. Compare this to the average biological value for other soy products, as well as different foodstuffs:

White flour: 41
Full-fat soy flour: 64
Soybean curd (tofu): 64
Whole wheat: 64
Immature bean: 65
Beef: 74.3
Fish: 76
Defatted soy flour: 81
Rice: 83
Cheese: 84
Cow milk: 90
Soybean milk: 91
Chicken egg: 94
Human milk: 95
Whole bean: 96

Health

In 1995, the New England Journal of Medicine(Vol.333, No. 5) published a report from the University of Kentucky entitled, "Meta-Analysis of the Effects of Soy Protein Intake on Serum Lipids." It was financed by the PTI division of DuPont,"The Solae Co." St.Louis. This meta-analysis concluded that soy protein is correlated with significant decreases in serum cholesterol, Low Density Lipoprotein LDL(bad) cholesterol and triglyceride concentrations. However, High Density Lipoprotein HDL (good) cholesterol did not increase. Soy phytoestrogens(isoflavones:genistein and daidzein) adsorbed onto the soy protein were suggested as the agent reducing serum cholesterol levels. On the basis of this research PTI,in 1998, filed a petition with FDA for a health claim that soy protein may reduce cholesterol and the risk of heart disease.

The FDA granted this health claim for 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." One serving,(1 cup or 240 mL) of soy milk, for instance,contains 6 or 7 grams of soy protein.

In, January ,2006 an American Heart Association review (in the journal "Circulation") of a decade long study of soy protein benefits casts doubt on the FDA allowed "Heart Healthy" claim for soy protein. The panel also found that soy isoflavones do not reduce post menopause "hot flashes" in women nor do isoflavones help prevent cancers of the breast, uterus or prostate. Thus, soy isoflavones in the form of supplements is not recommended. Among the conclusions the authors state, "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."

The original paper is in the journal Circulation: January 17,2006

Soy is also rich in estrogenic compounds such as genistein and diadzein, however, research is conflicing as to whether or not it can cause increases in estrogen in men.

Uses

Textured Soy Protein

Further information: Textured soy protein

TSP is made by forming a dough from high nitrogen solubility index(NSI) defatted soy flour with water in a screw type extruder such as the Wenger and heating with or without added steam. The dough is extruded through a die into various possible shapes; granules, flakes, chunks, goulash, steakettes (schnitzle), etc., and dried in an oven. TSP made from soy flour contains 50% soy protein and needs to 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 that is similar in texture to meat.

While TSP has a shelflife 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.

TSP can replace ground beef in most recipes, completely or partly. It can also replace up to 33% "tuna" fish in tuna salad. It is high in protein and low in fat and sodium. It is also a good source of fiber and isoflavones.

Notes and references

Health Effects of Low Furan Levels in Foods Examined
http://www.truestarhealth.com/members/cm_archives12ML3P1A8.html The Scoop on Protein Powders By Sofia Segounis, Nutritionist
Liu, KeShun (1997-05-01). Soybeans : Chemistry, Technology, and Utilization. Springer. p. 532. ISBN 0834212994. Citation on p.391 from Watanabe, et al., 1971 (in Japanese) {{cite book}}: |format= requires |url= (help); Cite has empty unknown parameter: |chapterurl= (help)
"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.
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.
http://www.jbc.org/cgi/reprint/10/6/433.pdf Mendel B., Fine M., Utiliztion of Legume Proteins, J Biol Chem, p 437, Septebmer 25, 1911
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
FAO/WHO . Expert consultation on protein quality evaluation. Food and Agriculture Organization of the United Nations, Rome.
FAO/WHO/UNU . Expert consultation. Energy and protein requirements. Technical Report Series 724. World Health Organization, Geneva.
^ http://mycause.com/bjw/AKSmith-SJCircle-soy-protein.pdf Cite error: The named reference "1972bv" was defined multiple times with different content (see the help page).
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B.L. Dillingham, B.L. McVeigh, J.W. Lampe, and A.M. Duncan, "Effects of Soy Isoflavone Consumption on Reproductive Hormones in Healthy Young Men," Department of Human Biology and Nutritional Sciences, University of Guelph, Ontario, Canada. Fred Hutchinson Cancer Research Center, Seattle, Washington, USA

"Soy Protein". Soya.be. Soya. Retrieved August 17. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
"Soy Protein". ASASoya.org. American Soybean Association. Retrieved August 16. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
Smith,A.K. and Circle,S.J.1972. Soybeans: Chemistry and Technology. AVI publishing.
Liu,KeShun.1997. Soybeans: Chemistry,Technology, and Utilization.
Berk, Zeki.1992. FAO(UN)
Circulation
ACE: Soy is more than just a good source of protein

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