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

This paper is a study on the distribution of the denatured whey proteins and κ-casein in soluble and micelle-bound complexes in heat treated caprine and bovine milk (90 °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 β-LGs remained stable after heat treatment of both milk species, but bovine α-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 κ-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 κ-casein included also β-casein and αs2-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.