Effect of calcium chloride on the structure and in vitro hydrolysis of heat induced whey protein and wheat starch composite gels

The formation of heat induced whey protein isolate (WPI) and wheat starch (WS) gels in the presence of added calcium chloride (5–192 mM) has been examined. Thermal properties, including the onset temperature of starch gelatinization and protein denaturation, are defined by low amplitude oscillation on shear and modulated temperature differential scanning calorimetry. Upon heating and subsequent cooling, comparison of the storage modulus values bear information on the enhancement of protein aggregation by the electrolyte and the occurrence of phase separation phenomena between the two polymeric constituents in the mixture. Further confirmation of observed trends has been provided by measurements on textural hardness of gels in single cycle compression tests. Porous and aggregated microstructures are identified upon visual examination by environmental scanning electron microscopy. The gels were subjected to in vitro enzymatic hydrolysis and the role of calcium in reducing the extent of starch degradation by α-amylase has been established. It is evident from the results that ionic strength in the form of added calcium ions largely influences gelation kinetics of whey protein leading to significant variability in the hydrolytic potential of α-amylase on wheat starch.