Proteins peptic hydrolysate

Nagaoka, S., Miwa, K., Eto, M., Kuzuya, Y., Hori, G., and Yamamoto, K. 1999. Soy protein peptic hydrolysate with bound phospholipids decreases micellar solubility and cholesterol absorption in... 

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. 

In a recent work (Sitohy et al, 2001b) 100% methyl-, 59% ethyl- and 56% propyl-esters of (3-casein, and 52% methyl-, 36% ethyl- and 25% propyl-esters of a-lactalbumin were prepared. The degree of pepsinolysis (% DH) was enhanced considerably after esterification. Methyl esters of both proteins yielded the highest levels of DH. Compared to SDS-PAGE of peptic hydrolysates of native proteins, those of esterified (3-caseins demonstrated the... 

Enzymatic gelation of partially heat-denatured whey proteins by trypsin, papain, pronase, pepsin, and a preparation of Streptomyces griseus has been studied (Sato et al., 1995). Only peptic hydrolysate did not form a gel. The strength of the gel depended on the enzyme used and increased with increasing DH. Hydrolysis of whey protein concentrate with a glutamic acid specific protease from Bacillus licheniformis at pH 8 and 8% protein concentration has been shown to produce plastein aggregates (Budtz and Nielsen, 1992). The viscosity of the solution increased dramatically during hydrolysis and reached a maximum at 6% DH. Incubation of sodium caseinate with pepsin or papain resulted in a 55-77% reduction in the apparent viscosity (Hooker et al., 1982). 

These suggestions were tested experimentally by Wasteneys and Borsook (68), who found that a peptic hydrolysate of protein gave, in the presence of concentrated pepsin solution and emulsion droplets of benzene or benzaldehyde, appreciable synthesis of a complex, less soluble material. Without the oil drops, reaction was very much slower, as the data in Fig. 24 show. Emulsions of fats, however, were noncatalytic, and xylol, talc, kieselguhr and barium sulfate were but weakly effective in increasing the rate. If the original protein is only slightly degraded, the yield in the synthesis is independent of the presence of the catalyst, but. 

Table I. Optimum pH Values for Degradation of Soybean Protein with Proteases and Those for Resynthesis with the Same Proteases from a Peptic Hydrolysate of Soybean Protein (37)...

Protein Hydrolysates. Instead of ethyl hippurate, a peptic hydrolysate of ovalbumin was used as substrate for the resynthesis reaction (64). This substrate (300 mg) was dissolved in water, adjusted to pH 6.0 with NaOH and to 0.9 ml with additional water. An amino acid ester was added to produce a 22.2mM solution and the mixture preincubated at 37°C for 15 min. Papain (3 mg), dissolved in 0.1M L-cysteine (0.1 ml), was combined with the above-mentioned preincubation mixture and incubation carried out at 37°C. After 2 hr, 0.1N NaOH (10 ml) was added to stop the enzymatic reaction and the resulting solution allowed to stand for 3 hr to hydrolyze completely the remaining amino acid ester as well as the ester group from the peptide product. The free amino acid produced from the base-catalyzed hydrolysis of the amino acid ester was determined with an amino acid analyzer. The amount of the amino acid incorporated was obtained by subtracting the determined value from the initial concentration of amino acid ester. The data obtained with the same L-amino acid esters as used in the model experiment (above) are plotted along the ordinate of Figure 3. An excellent correlation is found between the data from the model experiment and those from this experiment using a protein hydrolysate. In Table III data are shown for the extent of covalent incorporation after 2 hr of various amino acid ethyl esters into the protein hydrolysate. There is a close relationship between... 

Yamashita et al. (65) incorporated L-methionine into a soybean protein hydrolysate by means of the plastein reaction with papain. A 10 1 mixture of a peptic hydrolysate of soybean protein isolate and L-methionine ethyl ester was incubated in the presence of papain, the conditions being similar to those mentioned above. The methionine content of the plastein was 7.22 wt %, nearly seven times the original methionine content of the soybean protein isolate. To determine the location of the incorporated methionine residues, the plastein was treated with carboxypeptidase A. Methionine was liberated much faster than any other amino acid. A second portion of the plastein was methylated and then treated with lithium borohydride to reduce the COOH to CH2OH. Hydrolysis of the chemically treated plastein with 6N HC1 gave aminols in satisfactory yields. Subsequently, the aminols were converted to their DNP-derivatives, which were separated by thin layer chromatography. These experiments, together with some others, showed that 84.9% (molar basis) of the C-terminals of the plastein molecules were occupied with methionine, whereas only 14.4% of the N-terminals contained methionine. 

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. 

The plastein reaction was also investigated for the possible use of proteins in novel food applications. This was done via establishing a relationship between the microenvironmental conditions of the plastein reaction and the amino acid composition of the products. At low substrate concentration, produced by manipulation with additives, the plastein reaction was enhanced via the condensation pathway 174,75]. The plastein activity in the presence of a-chymotrypsin as catalyst increased with substrate concentration in the range of 10-30% (w/v). The substrate of this plastein reaction was a peptic hydrolysate of albumin obtained at 40°C, pH 7.0. The content of hydrophobic amino acids, in this case lie, Leu, Val, and Tyr, increased in the plastein products, while the content of Asp, Glu, Ser, and... 

Figure 5 Allergenic activity of the EPM products produced from different proteolytic hydrolysates of buffalo s milk proteins. (1) Buffalo s milk proteins (control) (2) peptic EPM product produced from a peptic hydrolysate (without amino acid enrichment) (3,4,5,6,7) peptic EPM products with different EPM enrichment from the peptic hydrolysates (8) peptic EPM product produced from the peptic and tryptic hydrolysate (without amino acid enrichment) (9,10,11,12,13) peptic EPM products with different Met enrichment produced from the peptic and tryptic hydrolysate of the buffalo milk proteins. The allergenic activity of the samples was measured in vitro by competitive indirect ELISA.

Figure 7 Allergenic character of products obtained from cow s milk proteins by food processing or enzymatic modifications. (1) Cow s milk (2) Na-caseinate (3) kefir (4) yogurt (5) cheese (6,7,8) a-chymotryptic, tryptic, and peptic hydrolysates of casein, respectively (9,10,11) a-chymotryptic tryptic, and peptic EPM products of casein, respectively (12,13) a-chymotryptic and tryptic EPM products of casein, respectively, with methionine enrichment (14,15) fractions of a-chymotryptic EPM products of casein (16,17) fractions of peptic EPM products of casein (18) commercial hypoallergenic formula.

Bitter peptides from peptic soya protein hydrolysates... 

Similar results as ours have recently been published by Zakar-ia and McFeeters (24). They studied the emulsifying activity of soy protein hydrolysates made by peptic hydrolysis and observed that with an increasing concentration of free amino groups in the hydrolysate the emulsifying activity exhibited an increase followed by a decrease. However, because of the differences in experimental conditions between their work and ours, a quantitative comparison would not be justified. 

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. 

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