Thermal densturation of glycinin as a function of hydration

Abstract

AbstractHydration effects on the thermal stability of glycinin (soybean 11S protein) were examined by differential scanning calorimetry (DSC). In a model system with pure glycinin, the denaturation temperature (Td) decreased with increasing moisture. Between 22 and 44% moisture, two endotherms were observed, where the lower‐temperature endotherm became progressively reduced in magnitude with a concomitant increase in a higher‐temperature transition. At 45.5% moisture, only a single endotherm was observed. The regression curves over the entire moisture range from 2 to 66% were derived as asymptote functions, where M equals the percentage total moisture. Equations were developed from the curves, and the relationship between Td and moisture were: Td=92.4+196.5e−0.068M and, for the low‐temperature endotherm, 82.4+144.3e−0.068M. By interaction of 11S protein with either ethanol, a neutral detergent (Triton X‐100) or 40% sucrose, both one‐ and two‐endotherm curves were generated. Such calorimetric behavior is indicative of nonequilibrium denaturation and supports the notion that structure reorganization during DSC is water content‐dependent. Our findings suggest that either glycinin’s acidic/basic subunits or a change in secondary protein structure may give rise to two endotherms.