Chemistry: natural resins or derivatives; peptides or proteins; – Proteins – i.e. – more than 100 amino acid residues – Plant proteins – e.g. – derived from legumes – algae or...
Reexamination Certificate
1999-08-25
2001-11-06
Carlson, Karen Cochrane (Department: 1654)
Chemistry: natural resins or derivatives; peptides or proteins;
Proteins, i.e., more than 100 amino acid residues
Plant proteins, e.g., derived from legumes, algae or...
C530S370000, C530S372000, C530S376000, C530S377000, C530S378000, C530S414000, C530S418000
Reexamination Certificate
active
06313273
ABSTRACT:
BACKGROUND
Soy proteins are valuable ingredients in foods due to their high nutritional value.
Soy proteins have found wide acceptance in Asia and are one of the principal sources of protein in a traditional Asian diet. Soy protein has not been as widely accepted in North America. Many American consumers object to the flavor of soy.
Raw soybeans and soy flour are characterized by odors described as green, grassy, bitter and beany and are therefore undesirable to many consumers. Volatile compounds contributing to soy flavor have been identified in numerous publications over the past 4 decades. A review of soy flavor (MacLeod, G. & Ames, J., (1988) Soy flavor and its improvement,
CRC Critical Reviews in Food Science and Nutrition
. 27 (4): 219-400) stated that 334 separate volatile compounds had been identified from soybeans, flours, concentrates, isolates, and textured soy proteins. The compounds identified were from the chemical classes of aliphatic hydrocarbons, alicyclic hydrocarbons, terpenoids, aliphatic alcohols, aliphatic aldehydes, aliphatic ketones, alicyclic ester, aliphatic ethers, aliphatic amines, aliphatic nitrile, chlorine containing compounds, benzenoids, sulfur compounds, benzenoids, sulfur compounds, furanoids, thiophenoids, pyrroles, pyridine, pyrazines, and thiazoles.
Specific compounds that have been identified as volatile components contributing to soy flavor include ethyl vinyl ketone, n-hexanol, n-pentanol, n-heptanol, methanol ethanol, ethanal, propanal, acetone, pentane, pentanal, hexanal, n-hexanal, acetaldehyde, acetone, and 2-heptenal.
Volatile components in soy products may be formed from precursors in the soybean. Factors affecting the formation of these compounds are oxygen tension, enzymes, temperature, moisture content and the possible presence of accelerators and/or inhibitors. Lipid oxidation and the effect of heating on carbohydrates and proteins have the greatest effect on the formation of volatile compounds. Minor factors contributing to flavor compounds include thermal decomposition of phenolic acids and thiamin and the degradation of carotenoids (MacLeod & Ames, supra).
Blade, R. J. (1990) Factors influencing endogenous flavor compounds in soybeans Ph.D. Dissertation, Clemson University identifies 21 volatile compounds in stored soybeans with gas chromatography-mass spectrometer analysis (GC-MS). Some compounds were not identified due to the inavailability of reference compounds or limitations in the sensitivity of the GC-MS. Predominant compounds isolated included: acetic acid, 1-hydroxy-2-propanone, butyrolactone, 1,3-dihydroxy-2-propanone, 2,6-dimethoxyphenol, 4-methylphenol, 3-hydroxy-4-methylacetophenone, palmitic acid, and stearic acid.
The undesirable flavor associated with soybeans and soy products has prompted research to develop methods to improve soy flavor. Past studies have focused on 3 main ideas: (1) Inhibition or inactivation of the lipoxygenase enzyme, (2) Removal of flavor compounds and precursors of flavor compounds, and (3) Masking the unwanted flavor (MacLeod & Ames, supra).
One area where soy protein has gained wide acceptance, despite its flavor, is in the production of infant formula. Formula such as Isomil®, produced by the Ross Products Division of Abbott Laboratories, utilizes soy for the sole source of protein. Research has focused upon the removal of certain substances from the soy protein prior to its utilization in infant formula. These substances include nucleic acids, phytic acid (phytate), phytoestrogens, and the volatile substance described above. A commercially viable process for removing all of these substances has not been developed to date. Thus research efforts continue in the field
Phytic acid is inositol hexaphosphoric acid, and is part of a large class of compounds that influence the functional and nutritional properties of foods. The phytic acid content of soybeans is reported to be between 1.0 and 1.47% of the dry weight. This is about 60% of the total phosphorus in the soybean. The amount of phytic acid in soy flour has been reported to be as high as 2.24% (w/w). Phytate forms complexes with proteins and with mono- and divalent cations. Therefore, phytate in food components may cause the proteins and minerals to have limited bioavailability. Since phytate is associated with the proteins, protein products also have high levels of phytate.
Phytase is an enzyme that hydrolyzes phytic acid to myo-inisitol and inorganic phosphate. Phytases are special kinds of acid phosphatases that hydrolyze phosphate from phytic acid as well as other phosphorylated substrates. This enzyme is present in plants including seed and germinating beans. The use of phytase in soybeans is limited (Stutardi, Buckle, K. A. (1986) The characterisitic of soybean phytase,
Journal of Food Biochemistry
, (10: 197-216)).
Anno, T., Nakanishi, K., Matsuno, R., Kamikubo, T. (1985) Enzymatic elimination of phytate in soybean milk, Nippon Shokuhin Kogyo Gakkaishi, 32(3): 174-180, hydrolyzed phytate from soybean milk with free wheat phytase and immobilized phytase.
The phytic acid content in the soybean milk was from 0.52 to 1.11 mg/g. The optimum temperature of the phytase enzyme was from 45 to 50° C. The optimum pH of the enzyme was 5.0 to 5.7. The enzyme was stable from pH 3.5 to 7.0. At pH lower than 6.0 the soybean proteins precipitated out. Phytate and protein interacted and formed stronger complexes at acidic pH. This interaction was found to decrease the solubility of the proteins, and influence the hydration, emulsifying properties and dispersibility.
Nucleic acids are another substance that would be desirable to remove from soy protein. Infant formula incorporating soy protein produced via current commercial processes has significantly higher levels of nucleic acids than human breast milk. Defatted soybeans reportedly contain 1.66% ribonucleic acid. Nucleotides contain a nitrogenous base (pyrimidine or purine), a pentose and a phosphate. A nucleoside is a nitrogenous base and a pentose without a phosphate (Lehnigher, A. L., Nelson, D. L., Cox, M. M. (1993)
Principles of Biochemistry
. New York: Worth Publishers)
Phytoestrogens occur in a variety of plants including soybeans. Phytoestrogens are defined as plant substances that are structurally and functionally similar to the gonadol steroid, 17 B-estradiol, that produce estrogenic effects. The desirability of phytoestrogens depends upon the age and sex of the individual who is consuming the soy protein. Phytoestrogens are highly desirable in menopausal and peri-menopausal females. The phytoestrogen mimics the estrogen which the female is either no longer producing or is producing in much smaller amounts.
By contrast, since phytoestrogens are not found in human breast milk it would be desirable to minimize their levels in infant formula. A detailed review of the effects of phytoestrogens on mammals is reported by Kaldas and Hughes in
Reproductive and General Metabolic Effects of Phytoestrogens in Mammals, Reproductive Toxicology
, Vol. 3, pages 81-89 (1989).
As used herein, the terms “phytoestrogens” and “isoflavones” should be considered interchangable. The term “isoflavones” refers to the compounds having the following general formula, with specific compounds identified in Table 1.
TABLE 1
Chemical structures of isoflavones found in soybeans
Isoflavone
R
1
R
2
R
3
R
4
R
5
Daidzein
H
H
OH
OH
H
Genistein
OH
H
OH
OH
H
Glycitein
H
OCH
3
OH
OH
H
Daidzin
H
H
O-glucoside
OH
H
Genistin
OH
H
O-glucoside
OH
H
Glycitin
H
OCH
3
O-glucoside
OH
H
As described in Table 2, daidzin, genistin and glycitin are the beta-glucoside conjugate (glucones) moieties. Daidzein, genistein and glycitein are the unconjugated (aglucones) moieties. As used herein “daidzein, genistein and glycitein levels” include both the conjugated and unconjugated moieties. The typical ratio of genistein to daidzein to glycitein in soy protein is 67 to 30 to 3.
Soy proteins are typically in one of three forms when consumed by humans. These include flour (grits), concentrates, and isolates. All three types are made f
Ndife Louis I.
Nelles Lynn P.
Shallo Hilary
Thomas Ronald L.
Abbott Laboratories
Carlson Karen Cochrane
Dixon J. Michael
Tu Stephen
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