Soybean proteins hydrolysates

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. 

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. 

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. 

Figure 1. Effect of substrate concentration on the yield of 10% trichloroacetic acid (TCA)-insoluble fraction measured after a soybean protein hydrolysate (substrate) has been incubated with a-chymotrypsin (dotted curve) (42) or with immobilized a-chymotrypsin (solid curve) (43) at 37°C for 2 hr. The scale on the ordinate shows TCA-insolubility after incubation relative to that before incubation.

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. 

FIGURE 5.4 Solid-lipid microparticles (SLM) produced by spray chilling, (a) SLM loaded with lycopene, xl. 0 K, (b) SLM loaded with soybean protein hydrolysate, x500, and (c) SLM loaded with L. acidophilus and polydextrose, 500x. 

The sulfur amino acid content of soy protein can be enhanced by preparing plasteins from soy protein hydrolysate and sources of methionine or cystine, such as ovalbumin hydrolysate (plastein AB), wool keratin hydrolysate (plastein AC), or L-methionine ethyl ester [3082-77-7] (alkaU saponified plastein) (153). Typical PER values for a 1 2 mixture of plastein AC and soybean, and a 1 3 mixture of alkah-saponified plastein and soybean protein, were 2.86 and 3.38, respectively, as compared with 1.28 for the soy protein hydrolysate and 2.40 for casein. 

These compounds can be provided as a defined mixture or in the form of protein hydrolysates, such as lactoalbumin, or plant-derived hydrolysates, like colza (Deparis et al., 2003), soybean (Donaldson and Shuler, 1998 Heidemann et al., 2000 Ikonomou et al., 2001), wheat (Heidemann et al., 2000 Ikonomou et al., 2001 Ballez et al., 2004), and rice (Heidemann et al., 2000 Ikonomou et al., 2001 Ballez et al., 2004). Supplementation with yeast extract also provides additional amino acids. 

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. 

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)...

Of special interest is the pH, the third factor influencing plastein formation. The optima for most proteases for plastein formation generally lie in a narrow range of pH 4-7 (Table I) measured with soybean globulin hydrolysates. Pepsin, for example, is an acid protease, and one of its characteristics is high degradative activity at low pH. Even at pH 1 it is active and able to degrade proteins. As Yamashita et al. (37) have demonstrated, no appreciable amount of plastein is formed at pH 1-2... 

Arai et al. (69) have prepared a similar plastein from soybean protein on an enlarged scale and purified it by precipitation with 70% ethanol. Table IV shows the amino acid composition of this purified plastein in comparison with that of the soybean protein used in preparation of the protein hydrolysate. 

This system of preparing protein hydrolysates may be of general utility however, Roozen and Pilnik (12) treated a soybean isolate in an ultrafiltration reactor and experienced problems of a thickened retentate... 

Partial proteolysis of soybean proteins with endopeptidases has been used to remove flavor compounds and related fatty materials from soybean curd and defatted soybean flour (21). Certain soybean protein concentrates possess an undesirable beany and oxidized flavor. Treatment of soybean curd and defatted soybean flour with endopeptidases such as aspergillopeptidase A released off-flavor compounds such as 1-hexanal and 1-hexanol which could be removed from the hydrolysate by solvent extraction. The enzymically digested products had less odor, taste, and color than the starting material and were more stable to oxidative deterioration. 

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. 

Ortiz, S.E.M., Mauri, A., Monterrey-Quintero, E.S., Trindade, M.A., 2009. Production and properties of casein hydrolysate microencapsulated by spray drying with soybean protein isolate. Food Sci. Technol. 42, 919-923. 

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

Soya oil. See Soybean (Glycine soja) oil Soyapan . See Soybean (Glycine soja) flour Soya primary amine. See Soyamine Soyapropanediamine Soyapropylenediamine. See Soyaminopropylamine Soya protein hydrolysates, reaction prods, with coco-acyl chloride. See Cocoyl hydrolyzed soy protein... 

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