64. Factors Affecting the Solubility of Milk Powders. II. The Influence of Temperature of Reconstitution on Protein Solubility

Abstract

In the previous paper(1) it was shown that the heat treatment to which a milk powder is subjected during manufacture may result in the production of two distinct types of protein insolubility, namely insolubility due to denaturation of the protein while still in solution, and insolubility caused by over-heating the milk powder while in a dry state. The insolubility due to denaturation was shown to be independent of the temperature of reconstitution of the milk powder. On the other hand the insolubility due to dry heating was found to vary with the temperature of reconstitution, the protein being relatively insoluble when reconstituted in water held at 20° C, but completely soluble when mechanically stirred for 30 min. in water held at 90° C. It was suggested that this latter type of insolubility might be due to the removal of water of imbibition from the protein particles, since such an explanation would account for the effect of hot water in restoring the solubility of the protein. In the previous paper, however, observations on the effect of temperature of reconstitution were limited to the two extreme temperatures, i.e. 20 and 90° C.