The Nutritive Value Op Skim-milk Powders, with Special Reference to the Sensitivity of Milk Proteins to Heat '

In the commercial dehydration of raw Kquid skim milk the immediate practical objective is the production of a dry powder that may be conveniently stored and readily transported. The agency of dehydration is heat. In the merchandising of these powders emphasis is placed upon their high nutritive value, particularly as sources of protein, of calcium, and of vitamin G. It is commonly, if tacitly, assumed that they are equal in nutritive value to the solids of raw liquid skim milk. However, there is more than a remote possibiHty that the heat treatment to which they have been subjected has lowered their nutritive value, although little definite evidence to this effect has been found in the literature. In the drying of liquid skim mUk, there are times when the resulting products are scorched. This scorching is caused in différent ways, and under careful management it may be prevented. The point of interest here is that these scorched products are offered for sale through the various merchandising channels. In such cases there is ocular evidence that processing has changed the milk solids, but to what extcAt the nutritive value has deteriorated there is again no available evidence. While many types of equipment are used in the manufacture of dry skim-milk powders, only two distinct processes of dehydration are in general use, one the roller process, and the other the spray process. Powders made by the roller process are largely merchandised as animal feed, while the powders sold for human consumption are largely prepared by the spray process. Whether the powders produced by the two processes are of equivalent nutritive value is not definitely known. Of the 288,000,000 pounds of dry skim-milk powder produced in the United States in 1933, about 60 percent went into human consumption through such media as bakery goods, ice cream, confectioneries, and breakfast cereals. The remaining 40 percent was sold as animal feed. The former channels of consumption obviously represent the most particular and fastidious of ásales distribution, in which a scorched product is frowned upon because of its off color and taste. The animal-feed buyer is not opposed to the scorched product because of color or taste, but he does, and should, view it with some doubt on the score of its nutritive value.