Electrophoretic Changes of Casein by Heating and Influence of Sugars and Whey Protein

Abstract

A 2.5 per cent sodium caseinate solution or calcium caseinate solution was heated with or without sugars. After dialysis against phosphate-NaCl buffer (pH 7.3, 0.1), it was analyzed by electrophoresis. Influence of whey protein was also studied. The results obtained are as follows.
1. Heating at 100°C for 30 minutes brought about no marked change in the electrophoretic pattern of casein. By heating at 120°C for 30 minutes, both α-and β-casein peaks became flat and their mobilities and the proportion of the β-casein area decreased slightly. Heating at 130°C made this change more distinct. No differefice was found between sodium caseinate and calcium caseinate solutions as to the change above.
2. A casein solution containing 4 per cent lactose became brown after heating at 120°C for 30 minutes, but its electrophoretic pattern was not markedly different from that of heated one without sugar. When 4 per cent glucose was present, instead of lactose, the appearance of a sharpe and asymmetrical α-peak and a more distinct decrease of β-casein peak were observed. By increasing the lactose concentration to 10 per cent (120°C) or raising temperature to 125°C (4 per cent lactose), the changes became also apparent. By heating at 130°Cin the presence of lactose or glucose, coagulation took place and, therefore, electrophoresis could not be carried out. Sucrose had no effect in any case.
3. When a casein solution was heated with unfractionated whey protein at 75-95°C for ten minutes, β-lactogloobulin peak decreased or disappeared, and apparent α-casein peak became heterogeneous and increased. In this case, different electrophoretic patterns were observed in sodium caseinate-whey protein and calcium caseinate.whey protein mixtures. It was also shown that a more marked change (i.e., splitting) in α-casein peak occurred when a heated mixture was treated with rennet than when an unheated mixture was treated with rennet. A difference was also pointed out between the mixture treated with rennet after heating and that heated after rennet treatment. The cause for these phenomena was discussed.