Comparison of Water Vapor Sorption by Milk Powder Components

Abstract

Water vapor is absorbed by milk powder at sites dependent upon the relative pressure, P/Po, of the atmosphere to which the powder is exposed. Comparison of the water sorption isotherms for the protein, sugar, and mixed salts comparable with that found in milk powder indicated that at low P/Po water is bound primarily by the casein fraction in the powder. As the P/Po progresses toward 0.5, lactose becomes more active in water binding. At P/Po = 0.5 the lactose accumulates sufficient water to undergo transition from the glass to crystalline hydrate state. This phase transition is accompanied by a net loss of water by the powder and as the relative pressure rises above 0.5, the salts rapidly absorb moisture.