Water Sorption by Dry Milk Solids. I. The Effect of Processing Treatments on Volume Contraction

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Abstract
Dry milk solids occupy an important place in the dairy industry, being used for human food, animal feed and for some industrial purposes, with human consumption taking the largest amount. Among the human food uses most are affected by the dry milk solids--water relationships. For re- constituting to the fluid state complete solubility (actually colloidal disper- sion) is desirable. For use in bread making, which is one of the more important human uses, complete solubility is not required but the maximum ability to hold water in a fixed state is desirable. The effects of processing treatments upon solubility have been established and are well known. The factors affecting water sorption have not been established. It is the purpose of this study to investigate certain phases of this problem. Water sorption is the taking up of water by colloidal materials and hold- ing it with some degree of force. It includes absorption, an intramicellar phenomenon, and adsorption, a surface or intermicellar relationship. It is considered synonymous with hydration, but may be different from the mani- festation of "bound water" as commonly measured. Water sorption exhibits itself through a positive heat of reaction as contrasted to solution which is endothermic; through a lowering of the aqueous vapor pressure; through a swelling of the colloidal material showing a definite swelling pres- sure; and through a volume contraction of the entire system. REVIEW OF LITERATURE