Effect of Acetylation on Turbidity of Glycinin

Abstract

Acetylation of epsilon-amino groups of lysine residues changed the aggregational properties of glycinin isolated from soybean. Soy glycinin with lysine residue modifications of 0%, 65%, and 95% were used for the experiment. Aggregation was detected by turbidimetry at 500 nm. There was a shift in isoelectric point of glycinin to the acidic region as the result of acetylation and a decrease in the turbidity of the protein above the pI. The solubilization effect of NaCl around the pI was diminished by acetylation. Aggregation of native glycinin by CaCl2 above pH 6 was also suppressed by acetylation, the degree of which depended upon the degree of acetylation. Above neutral pH, thermal aggregation of glycinin was decreased as acetylation increased. The effects of NaCl and conglycinin, as suppressors of thermal aggregation, were also decreased as the result of modification.