Effects of heating and salts on aggregation and solubility of casein under acidic conditions
2017
Nakano, T. (Minami Nippon Dairy CO-OP Co. Ltd., Miyakonojyo, Miyazaki (Japan). Research Division) | Ueki, M. | Mizoguchi, R. | Takeshita, M. | Arima, Y. | Aoki, T.
The present study aimed to clarify the effects of heating and salts on the aggregation and solubility of casein under acidic conditions. The turbidity of whole casein solution increased with increasing temperature (50-90degC) and pH (3.30-3.50). Addition of NaCl to whole casein solution caused suppression of the turbidity. Addition of > 30 mM NaCl to the unheated casein solution at pH 3.30-3.50 caused insolubilization of casein, and the insolubilized casein was solubilized by heating with decreasing pH. Casein was insolubilized at < 25 mM NaCl by heating with increasing pH. In the absence of NaCl, the insoluble casein formed by heating comprised only alpha sub(S1)-casein and beta-casein, while insoluble form of the other casein constituents increased by heating at > 10 mM NaCl. The effects of Ca, Mg, phosphate, and citrate on the solubility of casein at pH 3.45 and its changes when heated were also examined. The behavior of casein toward heat and salts under acidic conditions is markedly different from that under neutral conditions.
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