Soybean protein hydrolysates, bitter

Fujimaki (77,78) condensed bitter soybean protein hydrolysates in a Plastein-Reaction (79) and obtained non-bitter protein-like products, unfortunately without determination of molecular weights. 

Enzymatic hydrolysates of various proteins have a bitter taste, which may be one of the main drawbacks to their use in food. Arai el al. [90] showed that the bitterness of peptides from soybean protein hydrolysates was reduced by treatment of Aspergillus acid carboxypeptidase from A. saitoi. Significant amounts of free leucine and phenylalanine were liberated by Aspergillus carboxypeptidase from the tetracosapeptide of the peptic hydrolysate of soybean as a compound having a bitter taste. Furthermore, the bitter peptide fractions obtained from peptic hydrolysates of casein, fish protein, and soybean protein were treated with wheat carboxypeptidase W [91], The bitterness of the peptides lessened with an increase in free amino acids. Carboxypeptidase W can eliminate bitter tastes in enzymatic proteins and is commercially available for food processing. 

From soybean protein hydrolysates several series of bitter peptides have been isolated. As an example Table XIV shows bitter peptides isolated by Fujimaki (69., 70) As before the high Q-values are evident. 

Kukman, I.L., Zelenik-Blatnik, M., and Abram, V. 1995. Isolation of low-molecular-mass hydrophobic bitter peptides in soybean protein hydrolysates by reversed-phase high-performance liquid chromatography. J. Chromatogr. 704, 113-120. 

Enzymes Unsaturated soybean phospholipid Encapsulation in the inner aqueous core Alleviate bitterness in protein hydrolysates [164]... 

Series of bitter peptides have been isolated from enzymatic hydrolysates of proteins, esp. casein and soybean protein. 

It is interesting to see that proteins with high Q-values above 1400 as e.g. soybean protein, casein wheat gluten, potato protein, Zein are the "parents" of bitter peptides, whereas no bitter peptides have been isolated from hydrolysates prepared from collagen or gelatin, proteins with Q-values below 1300. 

Solubilization of Protein. Fish protein concentrate has high nutritional quality as determined both from its essential amino acid composition and from animal feeding experiments. Unfortunately, the concentrate is quite insoluble in water because of its denaturation by the solvent extraction method used in processing thus it contributes no functional properties to a food and must be used in bakery products primarily. A potentially useful method of solubilizing the protein is by proteolysis (9-12). As is the case with protein hydrolysates of casein and soybean protein, bitter peptides are formed during the hydrolysis. Papain and ficin produce more of these bitter peptides than does Pronase, for example (12). Pronase was found to produce a more brothy taste (13). A possible method of removing the bitter peptides is to convert the concentrated protein hydrolysate to plastein by further proteolytic enzyme action (14) to remove the bitter peptides. 

In enzymic digestions, the structures of the released peptides will, of course, depend upon the specificity of the particular protease. Often the peptides exhibit a very undesirable bitter flavor. For example, Fujimaki et al. (22) have characterized seven bitter peptides in peptic hydrolysates of soybean proteins. Almost all the bitter peptides had leucine at the N or C termini, and the bitterness of the peptides could be reduced by treatment with exopeptidases such as carboxypeptidase A. 

Shipe, W.F., G.F. Senyk, R.A. Ledford, D.K. Handler, E.T. Wolff, Elavor and chemical evaluations of fresh and aged market milk, J. Dairy Sci., 63(Suppl. 1), p. 43, 1980. Chandran, R.C., K.M. Shahani, Milk lipases a review, J. Dairy Sci., 47, p. 471, 1964. Kwak, H., I.J. Jeon, S.K. Pemg, Statistical patterns of lipase activities on the release of short-chain fatty acids in Cheddar cheese slurries, J. Food Sci., 54, p. 1559, 1989. Murry, T.K., B.E. Baker, Studies on protein hydrolysis I — preliminary observations on the taste of enzymic protein hydrolysates, J. Sci. Food Agric., 3, p. 470, 1952. Fujimaki, M., M. Yamashita, Y. Okazawa, S. Aral, Diffusible bitter peptides in peptic hydrolyzate of soybean protein, Agric. Biol. Chem., 32, p. 794, 1968. 

Arai, S., M. Yamashita, H. Kato, M. Fujimaki, Applying proteolytic enzymes on soybean Part V. A nondialzable bitter peptide hydrolyzate of soybean protein and its bitterness in relation to the chemical structure, Agric. Biol. Chem., 34, p. 729, 1970. Arai, S., The bitter flavor due to peptides or protein hydrolysates and its control by bitterness — masking with acidic oligopeptides, in The Analysis and Control of Less Desirable Flavors in Foods and Beverages, G. Charalambous, Ed., Acad. Press, New York. p. 1, 1980. 

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