Studies on Whey Protein Concentrates. 1. Compositional and Thermal Properties

Abstract

Cheddar-cheese-type whey protein concentrates were studied for their compositional and thermal attributes. The samples were prepared from three milk systems, namely, skim milk, whole milk, and skim milk enriched with buttermilk. The concentrates from skim milk were lower in all fat components and higher in proteins, except for the membrane-associated protein. The buttermilk-enriched samples had the most membrane-associated components. The concentrates from whole milk and buttermilk-enriched, skim milk were similar in protein composition, except for membrane-associated protein. The whole milk samples had the highest concentrations of total and free fat components. Lactose content and mineral composition were similar for the three types of concentrates. Thermal properties and denaturation kinetics were examined by differential scanning calorimetry. The samples exhibited a single broad endothermic peak with the denaturation temperature near 76°C and the enthalpy ranging from 1.86 to 2.16 cal/g. The concentrates from skim milk had higher denaturation enthalpy, whereas the concentrates from buttermilk-enriched, skim milk had slightly higher thermal stability. The overall denaturation process for whey proteins followed the reaction order n = 1.5 with an activation energy ranging from 217 to 251 kJ/mol. The thermal properties were observed to be related to a number of compositional factors. The denaturation enthalpy was positively correlated with β-lactoglobulin and protein content, and negatively correlated with bound fat, membrane protein, and membrane-associated lipid components. The denaturation temperature correlated positively with phospholipid content, and the onset denaturation temperature correlated positively with iron content.