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{{Short description|A protein that is isolated from soybean}}
'''Soy protein''' is generally regarded as the storage ] held in discrete particles called protein bodies which are estimated to contain at least 60-70% of the total soybean protein. Upon ] of the ], the ] will be digested and the released amino acids will be transported to locations of seedling growth. ] proteins, such as soy, and ] belong to the ] 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 ] or "prolamines". Soybeans also contain biologically active or metabolic proteins such as enzymes, trypsin inhibitors, hemagglutinins, and cysteine proteases. The soy ] 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.
]
'''Soy protein''' is a ] that is isolated from ]. It is made from ] that has been ] and ]. Dehulled and defatted soybeans are processed into three kinds of high protein commercial products: ], 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.<ref>{{cite web|url=http://www.plantcell.org/content/7/7/945.full.pdf |title=Info |website=www.plantcell.org }}</ref> 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 2S ] storage protein.<ref>{{cite journal | pmc = 2570561 | pmid=18949071 | doi=10.2174/1874091X00802010016 | volume=2 | title=2S Albumin Storage Proteins: What Makes them Food Allergens? | year=2008 | journal=Open Biochem J | pages=16–28| last1=Moreno | first1=F. J. | last2=Clemente | first2=A. }}</ref><ref name="autogenerated1">{{cite journal | pmc = 3326064 | pmid=22514740 | doi=10.1371/journal.pone.0035409 | volume=7 | issue=4 | title=Scalable purification and characterization of the anticancer lunasin peptide from soybean | year=2012 | journal=PLOS ONE | pages=e35409| last1=Seber | first1=L. E. | last2=Barnett | first2=B. W. | last3=McConnell | first3=E. J. | last4=Hume | first4=S. D. | last5=Cai | first5=J. | last6=Boles | first6=K. | last7=Davis | first7=K. R. | bibcode=2012PLoSO...735409S | doi-access=free }}</ref> Legume proteins, such as soy and ], belong to the ] family of seed storage proteins called ] and ]s, or in the case of soybeans, ] and beta-conglycinin. Soybeans also contain biologically active or metabolic proteins, such as enzymes, ] inhibitors, ]s, and ]s very similar to ]. The soy ] storage proteins, important for human nutrition, can be extracted most efficiently by water, water plus dilute alkali (] 7–9), or aqueous solutions of ] (0.5–2 ] ≈ 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.


== History == == 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 ] 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. Soy protein has been available since 1936 for its functional properties. In that year, organic chemist ] designed the world's first plant for the isolation of industrial-grade soy protein called alpha protein.<ref>{{cite web|url=http://www.soyinfocenter.com/HSS/glidden.php|title=The Gliden Company|website=www.soyinfocenter.com}}</ref> 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 ] and Frank Calvert spun into an artificial silk that was then tailored into that now famous "silk is soy" suit that ] wore on special occasions. The plant's eventual daily output of 40 tons of soy protein isolate made the Soya Products Division into ]'s most profitable division.


At the start of ], Glidden sent a sample of Julian's isolated soy (alpha) protein to National Foam System Inc. (today a unit of ]) which used it to develop Aero-Foam,<ref>{{cite web |url=http://www.sosrubberintl.com/pdf/NMS120-aofxl-3.pdf |title=NMS 120 |website=www.sosrubberintl.com |access-date=2011-06-22 |archive-date=2003-03-09 |archive-url=https://web.archive.org/web/20030309185107/http://www.sosrubberintl.com/pdf/NMS120-aofxl-3.pdf |url-status=dead }}</ref><ref>{{cite web |url=http://www.shipserv.com/ShipServ/pages/attachments/208620-ma/0448MA0610w.pdf |title=Mariner's Annual: U.S. Coast Guard Approved Fire Fighting Foam Concentrates |access-date=2011-06-22 |url-status=dead |archive-url=https://web.archive.org/web/20111003234022/http://www.shipserv.com/ShipServ/pages/attachments/208620-ma/0448MA0610w.pdf |archive-date=2011-10-03 }}</ref> used by the ] 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 ] possible. When a ] 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.<ref>{{cite magazine| url=http://www.time.com/time/magazine/article/0,9171,850791,00.html | archive-url=https://web.archive.org/web/20081214183619/http://www.time.com/time/magazine/article/0,9171,850791,00.html | url-status=dead | archive-date=December 14, 2008 | magazine=Time | title=PRODUCTION: Navy Bean Soup | date=1943-12-06 | access-date=2010-05-23}}</ref>
During WWII, the fire-extinguishing hydrolyzed soy protein ], "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.


In 1958, ] of ], acquired Julian's Soy Products Division (Chemurgy) of the ] Paint Company, Chicago. Central Soya's ] Protein Division, in January 2003, joined/merged with ]'s soy protein business ], which in 1997 had acquired ]'s soy division, Protein Technologies International (PTI) in St. Louis. On May 1, 2012 ] announced its complete acquisition of ] from Bunge.<ref>{{cite web |url=http://www.solae.com/About-Solae/News-Center/News-Releases/2012/2012-0501-DuPont-Solae.aspx |title=DuPont Acquires Full Ownership of Solae |access-date=2012-05-01 |url-status=dead |archive-url=https://web.archive.org/web/20120509151055/http://www.solae.com/About-Solae/News-Center/News-Releases/2012/2012-0501-DuPont-Solae.aspx |archive-date=2012-05-09 }}</ref><ref>{{cite web|url=http://www.solae.com/|title=Food ingredient solutions for the food industry - DuPont - Danisco|website=www.solae.com}}</ref>
Food grade soy protein isolate first became available on ] ]. An edible soy isolate and edible spun soy fiber has also been available since 1960.


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.<ref>], ] Soyinfo Center, 2008</ref>{{rp|227–28}} 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.
Recently, soy protein popularity has increased due to its use in health food products.


== Food uses == == Food uses ==
Soy protein is used in a variety of foods such as ], ], ], beverage powders, ], ], frozen desserts, ], ], ], ], ], and pet foods. Soy protein is used in various foods, such as ]s, ]s, ]s, beverage powders, ]s, ], frozen desserts, ], ]s, ]s, ]s, ]s, and pet foods.<ref>{{Cite web|title=Soy Protein Applications - Soy proteins for animal feed - Nutrition & Biosciences|url=https://www.dupontnutritionandbiosciences.com/product-range/protein/soy-protein-applications/soy-protein-pet-food-animal-feed.html|access-date=2021-06-11|website=www.dupontnutritionandbiosciences.com|language=en-US}}</ref>


== Functional uses == == Functional uses ==
Soy flour or defatted soy flour (50% protein) glue which originally replaced the more expensive ] glue for ] ] is re-emerging as the glue of choice to replace toxic ] and ] glues with a ]-free soy glue.<ref>{{cite web|url=http://www.acs.org/content/acs/en/pressroom/newsreleases/2010/august/tofu-ingredient-yields-formaldehyde-free-glue-for-plywood-and-other-wood-products.html|title=Tofu ingredient yields formaldehyde-free glue for plywood and other wood products - American Chemical Society|website=American Chemical Society}}</ref><ref>{{cite web|url=http://whyfiles.org/2010/old-new-glue-for-plywood-composites/|archive-url=https://web.archive.org/web/20100902172826/http://whyfiles.org/2010/old-new-glue-for-plywood-composites|url-status=dead|archive-date=September 2, 2010|title=Old-new glue for plywood, composites|date=26 August 2010}}</ref><ref>{{cite web|url=http://www.gizmag.com/tofu-ingredient-for-formaldehyde-free-plywood-glue/16147/|title=Tofu ingredient used to create formaldehyde-free plywood glue|website=www.gizmag.com|date=27 August 2010}}</ref><ref>{{cite web |url=http://www.fpl.fs.fed.us/documnts/pdf2011/fpl_2011_wescott001.pdf |title=Sticking power from soya beans |access-date=2018-09-17 |archive-date=2017-05-14 |archive-url=https://web.archive.org/web/20170514112315/https://www.fpl.fs.fed.us/documnts/pdf2011/fpl_2011_wescott001.pdf |url-status=dead }}</ref><ref>{{cite web |url=http://www.fpl.fs.fed.us/documnts/pdf2014/fpl_2014_frihart001.pdf |title=Documents |date=2014 |website=www.fpl.fs.fed.us |access-date=2014-10-27 |archive-date=2014-10-27 |archive-url=https://web.archive.org/web/20141027184521/http://www.fpl.fs.fed.us/documnts/pdf2014/fpl_2014_frihart001.pdf |url-status=dead }}</ref><ref>{{cite web|url=http://www.soyinfocenter.com/HSS/if_laucks_and_soybean_glue.php|title=I.F. Laucks Co. and Soybean Glue|website=www.soyinfocenter.com}}</ref> Soy protein is used for ] and texturizing. Specific applications include ]s, ]s, ]s, cleaning materials, ], ]s, ], ], paper coatings, ]s/]s, ]s, ]s, and ] ]s.
Soy protein is used for ] and texturizing. Specific applications include ]s, ]s, ]s, cleaning materials, ], ]s, ], ]s, paper coatings, ]s/]s, ]s, ]s and ] ]s.


== Production methods == == 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 ] 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 ]. The curd is usually neutralized with ] to form the sodium proteinate ] before drying Edible soy protein "isolate" is derived from defatted soy flour with a high solubility in water, as measured by the ] (NSI). The aqueous extraction is carried out at a ] below 9. The extract is clarified to remove the insoluble material and the ] liquid is acidified to a pH range of 4-5. The precipitated protein-curd is collected and separated from the whey by ]. The curd is usually neutralized with ] to form the sodium proteinate ] before drying


Soy protein concentrate is produced by immobilizing the soy globulin ] while allowing the soluble ], soy whey proteins, and salts to be leached from the defatted flakes or ]. The protein is retained by one of several treatments: leaching with 20-80% ] ]/], leaching with aqueous ] 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. Soy protein concentrate is produced by immobilizing the soy globulin ] while allowing the soluble ], soy whey proteins, and salts to be leached from the defatted flakes or ]. The protein is retained by one or more of several treatments: leaching with 20-80% ] ]/], leaching with aqueous ] 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% ], 20% carbohydrates (2.7 to 5% crude ]), 6% ] and about 1% oil, but the solubility may differ. One ] of defatted soybean flakes will yield about 750 kg of soybean protein concentrate. All of these processes result in a product that is 70% ], 20% carbohydrates (2.7 to 5% crude ]), 6% ] and about 1% oil, but the solubility may differ. One ] of defatted soybean flakes will yield about 750&nbsp;kg of soybean protein concentrate.


== Product types == == 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, ]s and carbohydrates removed. Because of this, it has a neutral ] and will cause less gas due to bacterial ].


Processed soy protein appears in foods mainly in three forms; soy flour, soy protein isolates, and soy protein concentrates.<ref name=Sipos>E.S. Sipos. {{Webarchive|url=https://web.archive.org/web/20130403175931/http://www.asaim-europe.org/Backup/pdf/edibleuses.pdf |date=2013-04-03 }}</ref><ref name=Singh>{{Cite journal | doi=10.1111/j.1541-4337.2007.00025.x|title = Functional and Edible Uses of Soy Protein Products| journal=Comprehensive Reviews in Food Science and Food Safety| volume=7| pages=14–28|year = 2008|last1 = Singh|first1 = Preeti| last2=Kumar| first2=R.| last3=Sabapathy| first3=S. N.| last4=Bawa| first4=A. S.}}</ref>
Soy isolates are mainly used to improve the ] of meat products, but are also used to increase protein content, enhance flavor, and as an ]).

=== 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 ] which has had most of the nonprotein components, ]s and carbohydrates removed. Because of this, it has a neutral ] and will cause less ] than soy flours.<ref name=Sipos/>{{rp|11}}


Soy isolates are mainly used to improve the ] of meat products, but are also used to increase protein content, to enhance moisture retention, and as an ].<ref name=Sipos/><ref name=Singh/>
Soy protein isolate is used in health foods as it is a complete ] containing all the essential ]s. 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 ] and help prevent ], some ]s and ].{{citationneeded}} Currently, the ] is examining health concerns related to levels of the toxin ] in soy protein isolate and other foods.<ref></ref>


Pure soy protein isolate is used mainly by the ]. It is sometimes available in health stores or in the ] section of the ]. It is usually found combined with other food ]s. Pure soy protein isolate is used mainly by the ]. It is sometimes available in health stores or in the ] section of the ]. It is usually found combined with other food ]s.


=== Concentrates === === 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 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.<ref name=Sipos/><ref name=Singh/>


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 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; ]s, ] and spray dried. Because they are very digestible, they are well-suited for ], pregnant and lactating women and the ]. They are also used in ]s, milk replacers for ] and ]s, and even used for some non-food applications. 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 ]s, milk replacements for babies (human and ]), and even used for some nonfood applications.


=== Flours === === Flours ===
Soy flour, is made by grinding soybeans,into a fine powder. It comes in three forms: natural or full-fat (contains natural ]s); defatted (oils removed) with 50% protein content and with either high water solubility or low water solublity; and lecithinated (] added). As soy flour is ]-free, ]-raised ]s made with soy flour are ] in texture. Soy flour is made by grinding (usually cooked) soybeans into a fine powder. It comes in three forms: whole or full-fat (contains natural ]s); defatted (oils removed, made from ]) with 50% protein content and with either high water solubility or low water solubility; and lecithinated (] added to defatted flour). A history of soy flour and grits has been published.<ref>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).</ref> As soy flour is ]-free, ]-raised ]s made with soy flour are dense in texture.<ref name=Sipos/><ref name=Singh/>


Soy ]s are similar to soy flour except that the soybeans have been toasted and cracked into coarse pieces. Soy grits are similar to soy flour except the soybeans have been toasted and cracked into coarse pieces.


'']'' is a roasted whole soy flour used in ]. The earliest known reference to kinako dates from 1540 CE. A history of kinako has been published.<ref>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).</ref>
==Protein==
Soybeans are a source of ].<ref>http://www.truestarhealth.com/members/cm_archives12ML3P1A8.html The Scoop on Protein Powders By Sofia Segounis, Nutritionist </ref> Soybean protein is essentially identical to that of other ] ] {that is to say legume proteins in general, consist of 7S and 11S storage proteins} vegetable proteins.
However, 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 ]s that must be provided to the ] because of the body's inability to ] them. For this reason, soy is important to many ] and ]. The phrase 'complete protein' is not entirely agreed-upon in usage by the scientific community.


== Nutrition ==
One measure of a protein's use in nutrition is the Biological Value scale. Whole soybean has a BV value of 74, as compared to the rating of 100 for whole eggs. Soy has a lower protein value than all animal sources of protein for muscle growth according to the BV methodology.{{verification needed}}
Soybean protein is a ] since it provides all of the ] for human nutrition.<ref>{{cite web |url=http://www.nsrl.uiuc.edu/soy_benefits.html |title=National Soybean Research Laboratory |publisher=Nsrl.uiuc.edu |access-date=2011-09-29 |url-status=dead |archive-url=https://web.archive.org/web/20120304080126/http://www.nsrl.uiuc.edu/soy_benefits.html |archive-date=2012-03-04 }}</ref><ref>{{cite web|url=https://www.fda.gov/fdac/features/2000/300_soy.html|title=Soy: Health Claims for Soy Protein, Questions About Other Components|website=] }}</ref> Soybean protein is essentially identical to that of other ] ] (that is to say, legume proteins in general consist of 7S and ]), and is one of the least expensive sources of dietary protein.<ref>Derbyshire, E. et al.1976. Review: Legumin and vicilin, storage proteins of legume seeds" ''Phytochemistry'' 15:3.</ref> For this reason, soy is important to many ] and ].


Soy flour contains 50% protein.{{sfn|Lim|2012|p=637}}
Mendel and Fine (1911-1912) made the interesting observation that soybeans produce a positive nitrogen(N) balance in a human subject. Many N-studies since then have confirmed the fact that the digestibility and biological value of soy protein for humans is comparable in nutritional value and quality to animal proteins.<ref>"Nutritional Value of Food Protein Products", I.E. Liener; Table 7.7 page 219. In Smith and Circle, editors; "Soybeans: Chemistry and Technology." Published by The AVI Publishing Co. 1972. Westport,Connecticut.</ref>


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%.<ref>{{cite book |last= Liu |first= KeShun |title= Soybeans : Chemistry, Technology, and Utilization |type= Hardcover |date=1997-05-01 |publisher= Springer |isbn= 978-0-8342-1299-2 |quote = Citation on p.391 from Watanabe, et al., 1971 (in Japanese)|page= 532 }}</ref><ref>"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.</ref> Some studies on rats have indicated the biological value of soy protein isolates is comparable to animal proteins such as ] if enriched with the sulfur-containing amino acid methionine.<ref>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.</ref>
The original Protein Efficiency Ratio ] 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 ], ], ] (UNU) and the ] when judging the quality of protein is ], as it is viewed as accurately measuring the correct relative nutritional value of animal and vegetable sources of protein in the diet.<ref>FAO/WHO (1991) Protein Quality Evaluation Report of Joint FAO/WHO Expert

When measuring the nutritional value of protein, the original ] (PER) method, first proposed by ] and ] 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, ], ] and the ] when judging the quality of protein is the ], as it is viewed as accurately measuring the correct relative nutritional value of animal and vegetable sources of protein in the diet.<ref>FAO/WHO (1991) Protein Quality Evaluation Report of Joint FAO/WHO Expert
Consultation, Food and Agriculture Organization of the United Nations, FAO Food Consultation, Food and Agriculture Organization of the United Nations, FAO Food
and Nutrition Paper No. 51, Rome.</ref><ref>Schaafsma, G. (2000) 'The protein digestibility-corrected amino acid score. ''Journal of Nutrition'' 130, 1865S-1867S</ref> and Nutrition Paper No. 51, Rome.</ref><ref>Schaafsma, G. (2000) 'The protein digestibility-corrected amino acid score. ''Journal of Nutrition'' 130, 1865S-1867S</ref>
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 0.91, and soy concentrate 0.95. 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 0.91 for isolated soy protein, however when leveled down, they appear much closer.<ref>FAO/WHO/UNU . Expert consultation. Energy and protein requirements. Technical Report Series 724. World Health Organization, Geneva.</ref> This is because 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.<ref>FAO/WHO . Expert consultation on protein quality evaluation. Food and Agriculture Organization of the United Nations, Rome. </ref> 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.<ref>FAO/WHO . Expert consultation on protein quality evaluation. Food and Agriculture Organization of the United Nations, Rome.</ref>


=== Biological value ===
The digestibility of some soyfoods are as follows: steamed soybeans 65.3%, tofu 92.7%, soy "milk" 92.6%, soy protein isolate 93–97%.<ref>{{cite book |last= Liu |first= KeShun |title= Soybeans : Chemistry, Technology, and Utilization |url= |format= Hardcover |accessdate= |edition= |date=1997-05-01 |publisher= Springer |location= |language= |id= ISBN 0834212994 |doi = |pages= 532 |chapter= |chapterurl= |quote = Citation on p.391 from Watanabe, et al., 1971 (in Japanese) }}</ref>


{{Main|Biological Value}}
The PDCAAS value is different from the PER and the BV methods in measuring the quality of protein. The ] was based upon the amino acid requirements of growing rats, which noticeably differ to that of humans. The Biological Value method, which dates back to 1911 relies on nitrogen(N) retention as an indicator of protein quality. However, it does not take into account certain factors influencing the digestion of the protein. Nonetheless, the ] (BV) methodology is an accurate indicator of biological activity for protein quality and utilization in humans.<ref>Methods of Estimating Protein Quality by D.M. Hegsted.</ref><ref>Mitchell, H.H. A method for determining the biological value of protein. 1924 J. Biol. Chem., 58, 873.</ref><ref>Mitchell, H.H. and G.G. Carman. The biological value of the nitrogen of mixtures 1926 of patent white flour and animal foods. J. Biol. Chem., 68, 183.</ref><ref>Optimum Sports Nutrition: Your Competitive Edge, A Complete Nutritional Guide For Optimizing Athletic Performance; 1993, Chapter 12. by Dr. Michael Colgan</ref><ref></ref><ref></ref>


Another measure of a protein's use in nutrition is the ] scale, 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.<ref name="1991Report">Protein Quality-Report of Joint FAO’/WHO Expert Consultation, Food and Agriculture Organisation, Rome, FAO Food and Nutrition Paper 51, 1991.</ref> Whole soybean has a biological value of 96, and soy milk 91.<ref>Smith, A.K. and Circle, S.J.1972. Soybeans: Chemistry and Technology.Table7.7 page 219. AVI publishing.</ref>
Biological value is determined based this formula.


== Health effects ==
BV = (nitrogen retained / nitrogen absorbed) * 100


A meta-analysis concluded soy protein is ] with significant decreases in ] ], ] (LDL) cholesterol and ] concentrations.<ref name="anderson">{{cite journal | pmid = 7596371 | year = 1995 | last1 = Anderson | first1 = JW | last2 = Johnstone | first2 = BM | last3 = Cook-Newell | first3 = ME | title = Meta-analysis of the effects of soy protein intake on serum lipids | volume = 333 | issue = 5 | pages = 276–82 | doi = 10.1056/NEJM199508033330502 | journal = New England Journal of Medicine| doi-access = free }}</ref> ] (HDL) cholesterol did not change. Although there is only ] evidence for a possible mechanism, the meta-analysis report stated that soy ] &ndash; the ], ] and ] &ndash; may be involved in reducing serum cholesterol levels.<ref name=anderson/>
A BV of 100 would indicate complete utilization of a given dietary protein, in that 100% of the protein ingested was stored in the body with none lost. However, it is physically impossible to have a BV greater than 100. Having a BV of over 100 would suggest that more than 1 gram of nitrogen was stored for every 1 gram of nitrogen consumed. Since it is thermodynamically impossible for the body to store more nitrogen than is ingested, a BV of over 100 is equally impossible.


In 1999, the US ] granted 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."<ref>{{cite web|url=https://www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/LabelingNutrition/ucm064919.htm|title=Soy Protein and Risk of Coronary Heart Disease (21 CFR 101.82); Guidance for Industry: A Food Labeling Guide (11. Appendix C: Health Claims)|publisher=US Food and Drug Administration|date=January 2013|access-date=20 January 2017}}</ref> In 2019, the FDA reassessed and supported the 1999 health claim by looking at data from 46 randomized controlled trials.<ref>{{cite journal|author=Jenkins, =David J. A; Mejia, Sonia Blanco|year=2019|title=Cumulative Meta-Analysis of the Soy Effect Over Time|journal=Journal of the American Heart Association|volume=8|issue=13|pages=e012458|doi=10.1161/JAHA.119.012458|pmid=31242779 |pmc=6662359 }}</ref>
] protein scored the highest number of 100 to serve as a measuring stick. ] has subsequently been found to have the highest known biological value of any protein in humans.<ref>.</ref> Whey scored a 104 in its basic form relative to the original 100 egg scale.<ref>.</ref> Further testing validated, the biological value of protein for whole eggs is 100 and 104 for whey with soy protein scoring 74.


In 2006, an American Heart Association review of soy protein benefits indicated only weak confirmation for the cholesterol-lowering claim about soy protein.<ref name="aha">{{Cite journal | doi = 10.1161/CIRCULATIONAHA.106.171052 | pmid=16418439 | volume=113 | issue=7 | title=Soy protein, isoflavones, and cardiovascular health: an American Heart Association Science Advisory for professionals from the Nutrition Committee |date=February 2006 | journal=Circulation | pages=1034–44| last1=Sacks | first1=F. M. | last2=Lichtenstein | first2=A | last3=Van Horn | first3=L | last4=Harris | first4=W | last5=Kris-Etherton | first5=P | last6=Winston | first6=M | author7=American Heart Association Nutrition Committee. | doi-access=free | citeseerx=10.1.1.514.3629 }}</ref> 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.<ref name=aha/> 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."<ref name=aha/>
<table>
<tr><td>The table below shows the Biological Value rating of various common proteins.</td></tr>
<tr><td>Isolated Whey: 104</td></tr>
<tr><td>Whole Egg: 100</td></tr>
<tr><td>Cow's Milk: 91</td></tr>
<tr><td>Egg Whites: 88</td></tr>
<tr><td>Fish: 83</td></tr>
<tr><td>Casein: 80</td></tr>
<tr><td>Beef: 80</td></tr>
<tr><td>Chicken: 79</td></tr>
<tr><td>Soy: 74</td></tr>
<tr><td>Wheat Gluten: 54</td></tr>
<tr><td>Kidney Beans: 49</td></tr>
</table>


In 2012, the ] (EFSA) published a scientific opinion on isolated soy proteins and reduction of blood LDL-cholesterol concentrations.<ref name="EFSA">{{cite journal|doi=10.2903/j.efsa.2012.2555|title=Scientific Opinion on the substantiation of a health claim related to isolated soy protein and reduction of blood LDL-cholesterol concentrations pursuant to Article 14 of Regulation (EC) No 1924/2006|journal=EFSA Journal|volume=10|issue=2|page=2555|year=2012|doi-access=free}}{{dead link|date=October 2020}}</ref> 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 rejected ]s that 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.<ref>{{Cite journal|date=2010|title=Scientific Opinion on the substantiation of health claims related to soy protein and contribution to the maintenance or achievement of a normal body weight (ID 598), maintenance of normal blood cholesterol concentrations (ID 556) and protection of DNA, proteins and lipids from oxidative damage (ID 435) pursuant to Article 13(1) of Regulation (EC) No 1924/2006|journal=EFSA Journal|language=en|volume=8|issue=10|pages=1812|doi=10.2903/j.efsa.2010.1812|issn=1831-4732|doi-access=free}}{{dead link|date=October 2020}}</ref>
== 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) ] 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.


== Role in the growth of the soybean plant ==
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.
Soy protein is generally regarded as stored ] held 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 seed ], the protein will be digested, and the released amino acids will be transported to locations of seedling growth. ] proteins, such as soy and ], belong to the ] family of seed storage proteins called ] (11S globulin fraction) and vicilins (7S globulin), or in the case of soybeans, glycinin and beta-conglycinin.<ref>{{Cite web |url=http://ddr.nal.usda.gov/bitstream/10113/28505/1/CAIN779129409.pdf |title=Archived copy |access-date=2010-03-17 |archive-url=https://web.archive.org/web/20120227072910/http://ddr.nal.usda.gov/bitstream/10113/28505/1/CAIN779129409.pdf |archive-date=2012-02-27 |url-status=dead }}</ref><ref>{{cite book|url=https://books.google.com/books?id=PWPKptZ1Z9sC&q=comparison+of+soy+proteins+with+other+legume+proteins&pg=PA257 |title=Food proteins and their applications - Srinivasan Damodaran, Alain Paraf - Google Books |date=2001-06-15 |access-date=2011-09-29|isbn=978-0-8247-9820-8|last1=Damodaran |first1=Srinivasan |publisher=CRC Press }}</ref> Grains contain a third type of storage protein called ] or "prolamines". ], a legumin class reserve protein from ] seeds have six identical subunits. There is one hexameric protein in the rhombohedral unit cell.<ref>{{cite journal |pmid = 8289257 | doi=10.1016/S0022-2836(05)80040-3 | volume=235 | issue=1 | title=Crystallographic characterization and molecular symmetry of edestin, a legumin from hemp |date=January 1994 | journal=J. Mol. Biol. | pages=361–3| last1=Patel | first1=S. | last2=Cudney | first2=R. | last3=McPherson | first3=A. | s2cid=30690679 | url=http://www.escholarship.org/uc/item/5m39g85p }}</ref>


Soybeans also contain biologically active or metabolic proteins, such as enzymes, ], hemagglutinins, and cysteine proteases very similar to ]. The soy ] 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 the protein is close to being native or undenatured.<ref>{{cite journal | pmid = 7640527 | year = 1995 | last1 = Shewry | first1 = PR | last2 = Napier | first2 = JA | last3 = Tatham | first3 = AS | title = Seed storage proteins: Structures and biosynthesis | volume = 7 | issue = 7 | pages = 945–56 | doi = 10.1105/tpc.7.7.945 | pmc = 160892 | journal = The Plant Cell}}</ref> Soybeans are processed into three kinds of modern protein-rich products; soy flour, soy concentrate, and soy isolate.
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


For the 11S protein, glycinin, to fold properly into its hexagonal shape (containing six subunits, a ]), it must undergo a very limited proteolysis<ref>{{cite journal | pmc = 48298 | pmid = 1731337 | year = 1992 | last1 = Scott | first1 = MP | last2 = Jung | first2 = R | last3 = Muntz | first3 = K | last4 = Nielsen | first4 = NC | title = A protease responsible for post-translational cleavage of a conserved Asn-Gly linkage in glycinin, the major seed storage protein of soybean | volume = 89 | issue = 2 | pages = 658–62 | journal = Proceedings of the National Academy of Sciences of the United States of America | doi=10.1073/pnas.89.2.658| bibcode = 1992PNAS...89..658S | doi-access = free }}</ref><ref>{{cite journal | pmc = 144002 | pmid = 9501109 | year = 1998 | last1 = Jung | first1 = R | last2 = Scott | first2 = MP | last3 = Nam | first3 = YW | last4 = Beaman | first4 = TW | last5 = Bassüner | first5 = R | last6 = Saalbach | first6 = I | last7 = Müntz | first7 = K | last8 = Nielsen | first8 = NC | title = The role of proteolysis in the processing and assembly of 11S seed globulins | volume = 10 | issue = 3 | pages = 343–57 | journal = The Plant Cell | doi=10.1105/tpc.10.3.343}}</ref><ref>{{cite journal | doi = 10.1111/j.1432-1033.1993.tb18014.x | title = A high-order structure of plant storage proprotein allows its second conversion by an asparagine-specific cysteine protease, a novel proteolytic enzyme | year = 1993 | last1 = Muramatsu | first1 = Masayoshi | last2 = Fukazawa | first2 = Chikafusa | journal = European Journal of Biochemistry | volume = 215 | pages = 123–32 | pmid = 8344272 | issue = 1| doi-access = free }}</ref> in a manner similar to the cleavage of a ] from ] to obtain active ].
Soy is also rich in estrogenic compounds such as ] and ], however, research is conflicing as to whether or not it can cause increases in estrogen in men.<ref>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 </ref>


== Uses == == Uses ==

=== Textured Soy Protein ===
=== Textured soy protein ===
{{Details|Textured soy protein}} {{Details|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 ]. The ] ] changes the structure of the soy protein, resulting in a fibrous spongy matrix that is similar in texture to meat. Textured soy protein (TSP) is made by forming a dough from highly soluble (high NSI) defatted soy flour with water in a screw-type ], and heating with or without steam. The dough is extruded through a die into various possible shapes: ], flakes, chunks, ], steakettes (]), 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 or ]. The extrusion ] changes the structure of the soy protein, resulting in a fibrous, spongy matrix similar in texture to meat.


While TSP has a ] of more than a year when stored dry at ], it should be used at once or stored for no more than three days in the ] after rehydration. It is usually rehydrated with cold or hot water, but a bit of ] or ] can be added to quicken the process. While TSP has a ] of more than a year when stored dry at ], it should be used at once or stored for no more than three days in the ] after rehydration. It is usually rehydrated with cold or hot water, but a bit of ] or ] can be added to quicken the process.


Soy protein products such as TSP are used as low-cost substitutes in meat and ] products.<ref>{{cite book |author=Hoogenkamp, Henk W. |title=Soy protein and formulated meat products |publisher=CABI Pub |location=Wallingford, Oxon, UK |year=2005 |isbn=978-0-85199-864-0 }}</ref><ref>{{cite book |author=Joseph G. Endres |title=Soy Protein Products |publisher=AOCS Publishing |year=2001 |isbn=978-1-893997-27-1 }}</ref> 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 substitute ] has been used for more than 50 years as a way of inexpensively and safely extending ground beef up to 30% for ], without reducing its nutritional value.<ref>{{cite book |author1=Circle, Sidney Joseph |author2=Smith, Allan H. |title=Soybeans: chemistry and technology |publisher=Avi Pub. Co |location=Westport, Conn |year=1972 |isbn=978-0-87055-111-6 }}</ref><ref>{{cite book |author=Liu, KeShun |title=Soybeans : Chemistry, Technology, and Utilization |publisher=Aspen Publishers |location=Gaithersburg, Md |year=1997 |isbn=978-0-8342-1299-2 }}</ref><ref>{{cite book|url=https://books.google.com/books?id=MyaYPGhJQk0C&q=soy+applications+in+food,+++riaz |title=Soy applications in food - Mian N. Riaz - Google Books |access-date=2011-09-29|isbn=978-0-8493-2981-4|year=2006|last1=Riaz |first1=Mian N. |publisher=CRC Press }}</ref>
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 ==
<references/><div class="references-small">
*{{cite web | title=Soy Protein | publisher=Soya | work=Soya.be | url=http://www.soya.be/soy-protein.php | accessdate=August 17 | accessyear=2005 }}
*{{cite web | title=Soy Protein | publisher=American Soybean Association | work=ASASoya.org | url=
http://www.asasoya.org/Uses/protein.htm | accessdate=August 16 | accessyear=2005 }}
* Smith,A.K. and Circle,S.J.1972. Soybeans: Chemistry and Technology. AVI publishing.
*Liu,KeShun.1997. ''''.
*Berk, Zeki.1992. FAO(UN)
*Circulation
* ACE: Soy is more than just a good source of protein

==External links==
*
*


== See also == == See also ==
{{portal|Food}}
* ]
* ]
* ]
* ]
* ]
* ]s * ]s
* ]
* ]
* ] * ]
* ]

== References ==
{{Reflist}}

=== Works cited ===
*{{Cite book| last1 = Lim | first1 = T. K. | chapter = Glycine max | doi = 10.1007/978-94-007-1764-0_79 | title = Edible Medicinal and Non-Medicinal Plants | pages = 634–714 | year = 2012 | publisher = Springer| location = Dordrecht, NL| isbn = 978-94-007-1763-3 }}

== External links ==

{{Soy}}


] ]
] ]
]

Latest revision as of 08:53, 11 December 2024

A protein that is isolated from soybean
Soybean pod

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 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 2S Albumin storage protein. 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 very similar to papain. 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 ≈ 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.

History

Soy protein has been available since 1936 for its functional properties. 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. 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.

Functional uses

Soy flour or defatted soy flour (50% protein) glue which originally replaced the more expensive casein glue for Douglas fir plywood is re-emerging as the glue of 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/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.

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. 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.

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 (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.

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 as casein if enriched with the sulfur-containing amino acid methionine.

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. 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.

Biological value

Main article: Biological Value

Another measure of a protein's use in nutrition is the biological value scale, 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.

Health effects

A meta-analysis concluded soy protein is correlated with significant decreases in serum cholesterol, low density lipoprotein (LDL) cholesterol and triglyceride concentrations. High density lipoprotein (HDL) cholesterol did not change. Although there is only preclinical evidence for a possible mechanism, the meta-analysis report stated that soy phytoestrogens – the isoflavones, genistein and daidzein – may be involved in reducing serum cholesterol levels.

In 1999, the US FDA granted 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, the European 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 rejected health claims that 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.

Role in the growth of the soybean plant

Soy protein is generally regarded as stored protein held 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 seed germinates, 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 (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 called gluten or "prolamines". Edestin, a legumin class reserve protein from hemp seeds 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 to papain. 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 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, a hexamer), it must undergo a very limited proteolysis in a manner similar to the cleavage of a peptide from proinsulin to obtain active insulin.

Uses

Textured soy protein

Further information: Textured soy protein

Textured soy protein (TSP) is made by forming a dough from highly soluble (high NSI) defatted soy flour with water in a screw-type extruder, 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 or supplement. The extrusion technology changes the structure of the soy protein, resulting in a fibrous, spongy matrix 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.

Soy protein products such as TSP are used as low-cost substitutes in meat and poultry products. 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 substitute textured vegetable protein has been used for more than 50 years as a way of inexpensively and safely extending ground beef up to 30% for hamburgers, without reducing its nutritional value.

See also

References

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Works cited

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