Moisture Studies in Dry Products of Milk. II. Estimating Water of Crystallization of Alpha-Lactose in Dry Whey Solids

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Abstract
For certain samples of dry whey solids it was found possible to estimate the water of crystallization of a lactose hydrate by observing the rate of moisture removal when a sample of 50 g. was distilled in the toluol distillation apparatus provided with a mercury-sealed stirrer. Because of the slow and unimolecular rate of dehydration of crystalline a lactose hydrate, a straight line was obtained after 20-30 min., when a plot of the logarithm of the moisture remaining against time was made. The % of water of crystallization of a lactose in the sample was estimated by extrapolating the linear portion to zero time. By this method it was found possible to differentiate quantitatively water of crystallization of a. lactose hydrate and water absorbed by casein. Furthermore, results obtained by this method were in close agreement with those by an indirect method in which the difference between total moisture, as detd. by the Karl Fischer method, and "free" moisture, as detd. by dehydration at 65 C and 2-3 mm. Hg pressure was considered to be water of crystallization of lactose. Aside from an effect on the rate of dehydration, particle size, within the range of 54 to 210 u, had no influence on the results obtained by the moisture desorp-tion method.