Chitosan-Soyprotein Interaction as Determined by Thermal Unfolding Experiments

Abstract

Chitosan interaction with soybean β-conglycinin β₃ was investigated by thermal unfolding experiments using CD spectroscopy. The negative ellipticity of the protein was enhanced with rising solution temperature. The transition temperature of thermal unfolding of the protein (T_m) was 63.4 °C at pH 3.0 (0.15 M KCl). When chitosan was added to the protein solution, the T_m value was elevated by 7.7 °C, whereas the T_m elevation upon addition of chitosan hexamer (GlcN)₆ was 2.2 °C. These carbohydrates appear to interact with the protein stabilizing the protein structure, and the interaction ability could be evaluated from the T_m elevation. Similar experiments were conducted at various pHs from 2.0 to 3.5, and the T_m elevation was found to be enhanced in the higher pH region. We conclude that chitosan interacts with β-conglycinin through electrostatic interactions between the positive charges of the chitosan polysaccharide and the negative charges of the protein surface.