'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 1936 for its functional properties. In 1936, African-American organic chemist
Percy Lavon 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, Dr. 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 which Henry Ford wore on special occasions. The plant's eventual daily output of forty tons of soy protein isolate made the Soya Products Division, Glidden's most profitable division.
During WWII, the fire extinguishing, soy protein foam, "Aero-Foam", the U.S. Navy's beloved fire-fighting "bean soup", was the brainchild of Percy Lavon Julian. When a
hydrolyzate 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, particularly useful on aircraft carriers.
In 1958, Central Soya of Fort Wayne,Indiana acquired Julian's, Soy Products Division (Chemurgy) of the Glidden Paint Company, Chicago. Recently, Central Soya's (Bunge) Protein Division, in January,2003, joined/merged with DuPont's soy protein (Solae) business,which in 1997 had acquired Ralston Purina's soy division, Protein Technologies International (PTI), St. Louis, Missouri. Eighth Continent, an "ersatz" soy milk is a combined "venture" product of DuPont's Solae, protein isolate and General Mills with a production facility in Minneapolis,MN.
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 has also been available, since 1960, from Ralston Purina Company of St.Louis,Ill. who had hired Boyer and Calvert. In 1987, PTI became the world's leading maker of isolated soy protein.
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 fibres.
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 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.
[1]
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.
Nutrition
Soybeans are considered a "
complete protein" source in that they provide all the
essential amino acids for human nutrition.
[2] However, some scientific sources disagree on this as the best measure of "complete protein." Soybean protein is essentially identical to that of other
legume pulses (that is to say, legume proteins in general consist of 7S and 11S storage proteins), and is one of the least expensive sources of dietary protein. For this reason, soy is important to many
vegetarians and
vegans.
Of any studied legume, whole soybeans have the highest levels of
phytic acid, an
organic acid and mineral
chelator present in many plant tissues, especially
bran and
seeds, which binds to certain ingested minerals: calcium, magnesium, iron, and especially zinc — in the intestinal tract, and reduces the amount the body assimilates. For people with a particularly low intake of essential minerals, especially young children and those in
developing countries, this effect can be undesirable. However, dietary mineral chelators help prevent over-mineralization of joints, blood vessels, and other parts of the body, which is most common in older persons.
The digestibility of some soyfoods are as follows: steamed soybeans 65.3%, tofu 92.7%, soy "milk" 92.6%, soy protein isolate 93–97%.
[3][4] Some studies on rats have indicated that the biological value of soy protein isolates is comparable to animal proteins such as casein if enriched with the sulfur-containing amino acid methionine.
[5]
Lafayette 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 succeeding mixed diets''".
[6]
When measuring the nutritional value of protein, the original Protein Efficiency Ratio
PER method first proposed by Osborne and 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 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.
[7][8]
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.
[9] 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.
[10]
Biological value of soy protein
''Main Article:
Biological Value''
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 a measurement of protein quality. However, it does not take into account certain factors influencing the digestion of the protein. Nonetheless, the
Biological Value (BV) methodology is an accurate indicator of biological activity for protein quality and utilization in humans.
[11][12][13] Soybean protein isolate has a BV of 74 as compared to egg white protein at 83.
[14][15]
According to the 1972 publication ''Soybeans: Chemistry and Technology'' which quotes studies dating as far back as the 1940s, highly refined isolated soy protein has an average biological value of 71.
[16] 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
[17]
★ Fish: 76
★ Defatted soy flour: 81
★ Rice: 83
★ Cheese: 84
[18]
★ Cow milk: 90
★ Soybean milk: 91
★ Chicken egg: 94
[19]
★ 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."[1] 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, fibre, 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."
[20]
The original paper is in the journal Circulation: January 17,2006.
[21]
Soy is also rich in estrogenic compounds such as
genistein and
daidzein, however, research is conflicting as to whether or not it can cause increases in estrogen in men.
[22]
A recent study found that 56g of soy protein powder per day caused serum testosterone to fall 19% in four weeks in a test group of twelve healthy males.
[23]
Uses
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; , 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
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.
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 fibre and isoflavones.
References
1. Health Effects of Low Furan Levels in Foods Examined
2. http://www.fda.gov/fdac/features/2000/300_soy.html Soy: Health Claims for Soy Protein, Questions About Other Components
3. Soybeans : Chemistry, Technology, and Utilization, , KeShun, Liu, Springer, , ISBN 0-8342-1299-4
4. "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.
5. 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.
6. 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
7. 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.
8. Schaafsma, G. (2000) 'The protein digestibility-corrected amino acid score. ''Journal of Nutrition'' 130, 1865S-1867S
9. FAO/WHO [1990]. Expert consultation on protein quality evaluation. Food and Agriculture Organization of the United Nations, Rome.
10. FAO/WHO/UNU [1985]. Expert consultation. Energy and protein requirements. Technical Report Series 724. World Health Organization, Geneva.
11. The Great Animal Versus Vegetable Protein Debate What Is The Best Protein For Muscle Growth? By Dr. Bill Misner, Ph.D. Article
12. The Use Of Biological Value Of A Protein In Evaluting Its Quality For Human Requirments
13. Nutritional Evaluation of Protein Foods
14. Max Muscle Sports & Fitness: Whey Protein with Dorian Yates By Dorian Yates: Table System. Article
15. Protein Quality-Report of Joint FAO’/WHO Expert Consultation, Food and Agriculture Organisation, Rome, FAO Food and Nutrition Paper 51, 1991.
16. http://mycause.com/bjw/AKSmith-SJCircle-soy-protein.pdf
17. http://www.enc-online.org/pdf/Presentations/TheNutritiousEgg.pdf
18. Jolliet, P. "Enteral nutrition in intensive care patients: a practical approach." Intensive Care Medicine (1998).
19. http://www.medbio.info/Horn/Time%206/protei4.gif
20. Soy Protein, Isoflavones, and Cardiovascular Health: An American Heart Association Science Advisory for Professionals From the Nutrition Committee -- Sacks et al. 113 (7): 1034 -- Circulation Article
21. Soy Protein, Isoflavones, and Cardiovascular Health. An American Heart Association Science Advisory for Professionals From the Nutrition Committee -- Sacks et al., 10.1161/CIRCULATIONAHA.106.171052 -- Circulation Article
22. B.L. Dillingham, B.L. McVeigh, J.W. Lampe, and A.M. Duncan, (2005). "Soy Protein Isolates of Varying Isoflavone Content Exert Minor Effects on Serum Reproductive Hormones in Healthy Young Men" ''Journal of Nutrition'', 135.
23. Goodin, Susan et al. (2007) , Clinical and Biological Activity of Soy Protein Powder Supplementation in Healthy Male Volunteers, ''Cancer Epidemiology Biomarkers & Prevention'', vol.16
External links
★
Different types of soy protein explained
See also
★
Edible protein per unit area of land
★
Soybeans
★
Soy milk
★
Textured soy protein
★
Soy allergy
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