The proteolytic action of rennet, pepsin and trypsin upon milk pasteurized at various temperatures has been investigated. It was shown that the action of these enzymes in pasteurized milk differed from their action on raw milk. The change was especially marked over the temperature range of 150–160° F., and was shown to be due, not to alteration in the protein itself, but probably to some change in the non-protein constituents of milk

The results were applied in a study of cheeses made from raw milk and from pasteurized milk. It was demonstrated, with the aid of cheeses ripened in the absence of bacterial action, that the differences in nitrogen partition which occur between cheeses made from raw milk and from pasteurized milk could be largely accounted for on the basis of chemical alteration produced in the milk constituents by heat treatment—this alteration affecting the proteolytic action of rennet and bacteria upon the cheese curd.