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Divisions of Dairy Husbandry and Agricultural Biochemistry University of Minnesota, St. Paul
ABSTRACT
The effect of freeze-drying milk on the physical state of certain milk constituents and on the keeping qualities of the resulting powder has been studied. The fat emulsion of freeze-dried powder is partially destabilized. The presence of free fat in the powder makes reconstitution difficult.
No crystallization of the lactose is evident in the spray- and freeze-dried powders. The data show that the ratio of ß to a lactose in these powders is dependent upon the temperature of drying. The ratio in spray-dried powder closely approaches the equilibrium ratio in a lactose solution at 212° F., while the ratio in freeze-dried powder closely approaches that at 32° F.
Flavor and keeping quality characteristics of freeze-dried milk are essentially the same as for spray-dried whole milk powder. Both dry milks have essentially the same flavor characteristics when fresh and both become tallowy in storage. They also may exhibit deterioration of the type associated with the Maillard reaction. The freeze-dried powder, however, frequently acquires a fruity flavor which is not apparent in spray-dried milk.
Freeze-drying by the methods used in this study does not produce a more satisfactory product than spray-dried milk.
1 Paper no. 2687 Scientific Journal Series, Minnesota Agricultural Experiment Station.
2 The data in this paper are taken from a thesis presented by T. A. Nickerson in partial fulfillment of the requirements for the Ph.D. degree, University of Minnesota, 1950.
3 Now at the University of California, Division of Dairy Industry, Davis.
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