Effects of acetylation of physicochemical and functional properties of glycinic

Abstract

Acetylation of $\varepsilon$-amino groups of lysine residues changed conformation of glycinin isolated from soy bean, the extent of which depended upon the degree of modification. Soy glycinin with lysine residue modifications of 0\%, 28\%, 65\%, 85\%, and 95\% were used for the experiment. Accessibility of tyrosine and tryptophan residues, which were shown to increase as modification percent increased, were detected using uv absorption spectra and fluorescence spectra, respectively. Surface hydrophobicity was found to increase more than times over native glycinin when lysine residues were excessively modified to above 95\%. Masking of charged lysine residues, exposure of hydrophobic interior, and subunit dissociation have contributed to the increase. Enthalpy, as obtained from differential scanning calorimetry, dropped from 3.6 cal/g native protein to 0 cal/g protein when lysine residues were acetylated above 65\%, implicating complete denaturation. The hydrolytic rates, using $\alpha$-chymotrypsin, increased initially, then decreased at more than 65\% lysine modification. Effect of the acetylation on turbidity of protein was investigated using samples of 0\%, 65\%, and 90\% acetylation. Turbidity of acetylated glycinin decreased and isoelectric point shifted to acidic region. Salts (NaCl, $CaCl_2$) were found to hardly affect turbidity of acetylated glycinin in contrast to native one. Sodium chloride depressed turbidity of native protein while that of 90\% modified sample was scarcely changed. Calcium chloride dramatically increased turbidity of native protein at above pH 7, while that of 90\% modified glycinin was hardly affected. Heat stability of glycinin was found to increase by acetylation. Conglycinin affected little on turbidity of acetlylated glycinin in contrast to the native protein. Emulsfying properties of acetylated glycinin was also checked using samples of 0\%, 45\%, and 90\% modification. At oil to protein solution ratio of 2.5:7, pH 7.6, 90\%...