Effect of Heat and Alcohol Extraction on the Nutritive Value of Casein

The methods employed for the purification of casein for experimental diets require either the use of solvents to extract extraneous materials or the application of heat to destroy the unwanted accessories, or both solvents and heat may be employed. Casein treated in either or both of these ways does not permit optimum growth in experimental animals. The experiments described below, which are, in many respects, similar to those reported from other laboratories, can readily be explained on the basis of the removal of a nutritional factor, with or without the coincident impairment of the protein itself.

An attempt was first made to demonstrate what effect, if any, alcohol extraction of casein might have on the value of a diet in supporting lactation in rats in the first and second generations. By the method of Kozlowska, McCay and Maynard, 1 lactation was studied on stock females which were fed the following diet beginning 2 days after parturition: protein, 18%; hydrogenated cotton-seed oil (crisco), 22%; corn starch, 41.5%; salts, 2 4.5%; agar agar, 2%; yeast,∗ 10%; cod liver oil, 2%. The protein was commercial casein (diet A) or casein which had been extracted in a percolator for 4 days with boiling 95% alcohol (diet B). This same method of extraction, first described by Sperry, was used for all preparations. At the end of the 40-day lactation period the young from these litters were continued on the same diet and their growth rate (Fig. 1) and lactation capacity were also studied.

From Table I it can be seen that lactation was much better on diet A than on diet B, but this difference was only slightly accentuated in the second generation. The growth rate of the second generation males was inferior on the extracted casein but the females did not show this difference (Fig. 1).