RHEOLOGICAL PROPERTIES AND CONFORMATIONAL STATES OF BETA-CONGLYCININ GELS AT ACIDIC PH

The heat-induced gelation of beta-conglycinin was investigated by dynamic viscoelastic measurements as a function of pH. At pH values below 5.5-6.0, the storage modulus G' rapidly increased with decreasing pH. The conformational states of both sols and gels of beta-conglycinin were investigated by Fourier transform ir (FTIR) and by differential scanning calorimetry (DSC). The degree of protonation of the carboxyl groups of beta-conglycinin, when examined by FTIR indicated that, as would be expected, the degree of protonation increased with decreasing pH below pH 6.0. DSC measurements suggest that beta-conglycinin tends toward thermal denaturation with decreasing pH (below pH 6.0). Second-derivative FTIR spectra for beta-conglycinin gels show that a band at 1620 cm(-1) (associated with exposed beta-strands) develops with decreasing pH. The results suggest that beta-conglycinin undergoes denaturation with increasing protonation of its carboxyl groups, resulting in an increase in the amount of exposed beta-strands. The exposed beta-strands then intermolecularly bond to form gel networks. This process is promoted with decreasing pH, and as a result, rigid gels form at acidic pH values. (C) 1994 John Wiley & Sons, Inc.