Modification of soy protein using the plastein reaction, phosphorylation, and ethylation, and their effects on functionality
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Date
1989
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Abstract
Soy protein isolate was modified using enzymatic hydrolysis and the plastein reaction. Soy protein and plastein were each also chemically modified by phosphorylation and ethylation. Only 34% of the hydrolysate's nitrogen was incorporated into the plastein. Increasing the substrate concentration from 30 or 40% to 50%, and the temperature from 37°C to 50°C, each increased the plastein yield marginally, while 20% [S] and 60°C each resulted in decreased yields. pH changes from the 4.5 to 5.0 range, altering the enzyme or E:S ratio, the incubation time, the plastein reaction solvent, or denaturing the protein with alkali were all found to have either no effect or a negative effect on yield. Chemical modification by either ethylation or phosphorylation also did not improve yield. Amino acid analysis of soy plastein revealed that it was significantly higher in the bulky hydrophobic or aromatic amino acids versus soy protein, much lower in the acidic amino acids, and somewhat lower in some of the basic, hydrophilic, and shorter chain hydrophobic ones. The chemically modified plasteins showed the same trend, except the differences from soy protein were accentuated. Seven functional tests were each done at pH 7.0 and 4.5 to evaluate the enzymatically and chemically modified samples. Plastein functionality was found to be intermediate between soy protein and hydrolysed soy protein, except in oil related functional properties, such as oil binding capacity, emusifying capacity, and emulsion stability, where it was superior to both..
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Typescript (photocopy).
Keywords
Proteins, Molecular rotation, Proteins, Separation, Proteins, Synthesis, Solubility, Food Science and Technology