Heat induced casein-whey protein interactions at natural pH of milk: A comparison between caprine and bovine milk

Abstract

This paper is a study on the distribution of the denatured whey proteins and kappa-casein in soluble and micelle-bound complexes in heat treated caprine and bovine milk (90 degrees C, 10 min) at natural pH (6.71). Proteins were fractionated using fractionation technique based on renneting and were analysed by three electrophoretic techniques: native PAGE, SDS-PAGE under reducing and non-reducing conditions. Lower than 3% of the total beta-LGs remained stable after heat treatment of both milk species, but bovine alpha-LA was more heat stable than its counterpart in caprine milk (29.6% against 3.82%). Denatured caprine whey proteins (>95%) were part of micelle-bound complexes whereas soluble complexes were not observed. Conversely, about 30% of denatured bovine whey proteins were involved in soluble complexes. About 24.2% of total kappa-CN was included into complexes formed in heat-treated bovine milk whereas in heat-treated caprine milk this percentage is about three times higher. Caprine micelle-bound complexes, apart from whey proteins and kappa-casein included also beta-casein and alpha(s2)-casein, which were not found in their bovine counterparts. This knowledge could be very useful in understanding the differences in technological-functional properties of caprine and bovine milk and to enable better control of dairy processes.