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Water Sorption by Dry Milk Solids. II. The Relation Between Volume Contraction and the Degree of Sorption

University of California

ABSTRACT

1. The volume contraction of dry milk solids prepared by different processing treatments was determined after different amounts of water had been added to the dry material.
   
2. From these data, curves were constructed which, when extrapolated to zero water concentration and zero contraction, gave values for maximum volume contraction and for maximum degree of sorption for each sample.
   
3. The maximum volume contractions at zero water concentration ranged from 42.6 cubic mm. per gram of dry material to 57.5 cubic mm. for the atmospheric roll-process samples, and from 69.2 cubic mm. per gram to 102.0 cubic mm. for the spray-process samples. These values correspond to degrees of sorption, expressed as percentage of the weight of the solids, respectively, as follows: 15.1 per cent, 18.5 per cent, 23.9 per cent and 36.3 per cent.
   
4. The volume contraction/degree of sorption ratio was found to be 2.88 ±.06 cubic mm./l per cent sorption, which compares with the expected value of 3–4 cubic mm./l per cent sorption. It is suggested that the reason for the low value for this ratio lies in the hydration of lactose in solution, with no accompanying volume contraction within the limits of concentration used here.