INGE GAZI, THOM HUPPERTZ*
*Corresponding author
NIZO food research, PO Box 20, 6710BA, Ede, The Netherlands

Abstract

Heat treatment of milk typically results in denaturation of whey proteins and their association with caseins. The functionality of the proteins can be affected by the presence of these aggregates and the distribution of the aggregates between the casein micelles and the serum phase. Casein-whey protein interactions are detrimental in (rennet-)cheese making, whereas the presence of aggregates in the serum phase during yoghurt making improves gelation properties and strengthens gel texture; micelle-bound aggregates increase the heat stability of milk, particularly in concentrated systems. The current knowledge and a strict control of the processing conditions create functionality of the dairy proteins that covers a very broad range of applicability.

INTRODUCTION

Milk proteins have always played a crucial role in the human diet. Mother’s milk provides essential proteins to the neonate, and at later stages in life, milk proteins are found in a vast range of popular and widely-consumed dairy and non-dairy food products. In addition to a crucial nutritional role, milk proteins also have an important role from a physicochemical perspective. They provide the texture of cheese and yoghurt, and also stabilize air bubbles in ice cream and whipped cream. Two different classes of milk proteins are distinguished, which show vastly different behaviour. Caseins represent the major class of proteins (~80% of total protein in cows’ milk). These phosphoproteins are organized in milk in spherical colloidal structures (diameter ~200 nm) called casein micelles, consisting of thousands of casein molecules linked together, amongst others, through calcium phosphate nanoclusters. The casein micelles are rather heat-stable, but coagulate at pH <5 or after addition of rennet. Casein micelles are crucial in converting milk into e.g., cheese or yoghurt. In contrast, the whey proteins (~20% of total protein in cows’ mi ...