Effect of sodium bisulfite on properties of soybean glycinin.

The objective of this work is to understand the function of glycinin in soy protein adhesive formation. Glycinin protein was treated with sodium bisulfite, and physicochemical, morphological, and adhesion properties of the modified soy glycinin were characterized. More disulfide bonds that associated acidic and basic polypeptides of glycinin broke as the sodium bisulfite concentration increased. The reduction of disulfide bonds did not decrease the thermal stability of glycinin. Instead, the denaturation temperature of modified glycinin increased as sodium bisulfite increased. Sodium bisulfite-induced disulfide bond cleavage increased the surface hydrophobicity of modified glycinin. Hydrophobic force is the main driving force for glycinin aggregation, and the balance between hydrophobic and electrostatic forces makes glycinin form chainlike aggregates. The adhesive strength and water resistance of glycinin dropped significantly at lower levels of sodium bisulfite and then increased as the amount of sodium bisulfite increased up to 24 g/L. The adhesive performance decreased again with further addition of sodium bisulfite. The adhesive strength of glycinin was not improved by sodium bisulfite modification in the studied range.