Effects of basic proteins on the denaturation and heat-gelation of acidic proteins

Abstract

This paper describes the heat-setting properties and thermal denaturation characteristics of solutions containing basic (high isoelectric point) and acidic (low isoelectric point) proteins at low ionic strength. Systems containing bovine serum albumin (BSA) and either clupeine (p I = 12) or a derivative of β-lactoglobulin (p I = 9.5) gelled on heating, sometimes at lower concentrations than BSA alone. However, the microstructures of the mixed protein gels were coarse compared to BSA gels formed in the presence of sodium chloride. They were also opaque and showed some tendency to synerese. At a high sucrose concentration, however, gelation was superior to that of acidic protein alone. It is proposed that in the mixed system, electrostatic forces of attraction are dominant in structure formation, in contrast to a single protein system. Differential scanning calorimetry showed that clupeine caused a reduction in both the temperature and enthalpy of denaturation of BSA and myoglobin, suggesting that perturbation of the acidic protein tertiary structure by the basic protein may have a secondary role in gelation.