Rheological properties and conformational states of β‐conglycinin gels at acidic pH

The heat‐induced gelation of β‐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 β‐conglycinin were investigated by Fourier transform ir (FTIR) and by differential scanning calorimetry (DSC). The degree of protonation of the carboxyl groups of β‐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 β‐conglycinin tends toward thermal denaturation with decreasing pH (below pH 6.0). Second‐derivative FTIR spectra for β‐conglycinin gels show that a band at 1620 cm−1 (associated with exposed β‐strands) develops with decreasing pH. The results suggest that β‐conglycinin undergoes denaturation with increasing protonation of its carboxyl groups, resulting in an increase in the amount of exposed β‐strands. The exposed β‐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.