Glycinin of more than 97% purity was modified using maleic anhydride. Glycinin samples of 0%, 65%, and 95% lysine residue modifications were used to determine the changes in turbidimetric characteristics of the protein due to maleylation. The solubility behavior of the protein as a function of pH was changed with maleylation. The isoelectric point of 65% and 95% modified glycinin shifted to pH 4.0 and pH 3.5-4.0, respectively, as compared to pH 4.6 for native glycinin. Maleylated glycinins exhibited increased solubility at pH above 4.6. Turbidity of native glycinin decreased substantially by the addition of NaCl, but the stabilizing effect of NaCl decreased when the protein was chemically modified. The effect of NaCl on 65% modified glycinin was intermediate between native glycinin and 95% modified sample. Thermal aggregation of native glycinin was completed within 5 min of heating at 80oC. Maleylation contributed significantly to the thermostability of the protein at pH of 7.0 and 9.0, exhibiting little turbidity. Addition of NaCl suppressed thermal aggregation of native glycinin, but turbidity actually increased for the samples of 65% and 95% modification.
Introduction
Materials and Methods
Results and Discussions