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Soy protein (Flour, concentrate,
powder, isolate TSP)
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, 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 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 ton 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.
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
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.
Soybean protein isolate has a biological value of 74. [11]
According to the 1972 publication Soybeans: Chemistry and Technology,
highly refined isolated soy protein has an average biological value of
71, which contrasts sharply with the biological value of whole
soybeans at 96, soybean milk (91), whole eggs (97) and cow's milk
(90).[12]
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
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 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
2. http://www.fda.gov/fdac/features/2000/300_soy.html Soy: Health
Claims for Soy Protein, Questions About Other Components
3. Liu, KeShun (1997-05-01). Soybeans : Chemistry, Technology, and
Utilization (Hardcover), Springer, 532. ISBN 0-8342-1299-4. “Citation
on p.391 from Watanabe, et al., 1971 (in Japanese)”
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., Utilization of Legume Proteins, J Biol Chem, p
437, September 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. Protein Quality-Report of Joint FAO’/WHO Expert Consultation,
Food and Agriculture Organisation, Rome, FAO Food and Nutrition Paper
51, 1991.
15. 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.
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