Effect of hydrocolloids on the thermal denaturation of proteins

The thermal denaturation of bovine serum albumin (BSA), lysozyme and whey protein isolate (WPI) in the presence of hydrocolloids (pectin, guar gum, ι-carrageenan) was investigated. A decrease in the thermal stability of lysozyme was observed in the mixture of protein with ι-carrageenan. The increase in the enthalpy of denaturation (ΔH) of BSA and lysozyme in the presence of hydrocolloids was attributed to the protection of globular proteins against aggregation through blockage of their hydrophobic binding sites by the bulky polysaccharide moeity. Biopolymers had a stabilizing effect on WPI. The thermal stability was the highest in the presence of pectin, whereas the lowest transition temperature was observed in the presence of guar gum. A single transition peak was observed for pure WPI. However, WPI exhibited two transition temperatures when together with pectin and i-carrageenan. WPI was stable against heat denaturation at acidic pH values (pH 4.0), while it was denatured at a low temperature at an alkaline pH (pH 9.0) in the presence of pectin. This was attributed to the formation of extra hydrogen bonding. The increase in the concentration of pectin has little affect on the heat stability of WPI; however, it reduces the cooperativity of transition.