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

University of California

ABSTRACT

1. The volume contraction of dry milk solids prepared by different processing treatments immersed in an unlimited amount of water has been measured at 20 degrees C. in a dilatometer.
   
2. Dry milk solids preheated at 76.7 degrees C. (170 deg. F.) for 30 minutes before drying showed greater volume contraction in water than solids preheated at other temperatures studied, namely 60 degrees C. (140 deg. F.) (roller only), 71.1 degrees C. (160 deg. F.), 82.2 degrees C. (180 deg. F.), and 93.3 degrees C. (200 deg. F.).
   
3. Dry milk solids manufactured by the spray process showed greater volume contraction than when manufactured by the atmospheric roller process.
   
4. The time required for volume contraction to be complete ranged from 20–22 hours for all spray samples except the one processed at 82.2 degrees C. (180 deg. F.) and 24–28 hours for all roller samples except 82.2 degrees C. (180 deg. F.) and 93.3 degrees C. (200 deg. F.) to 48 hours for the samples processed by the higher heat treatments mentioned.
   
5. The significance of the data is discussed in the light of known facts concerning volume changes accompanying various phenomena and the conclusion is drawn that the volume contraction probably results mainly from the sorption of water by the milk proteins.