Effects of Steam-Heating upon the Nutritive Value of Full-Fat Soybeans for Sheep and Rats

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Abstract
The effect of heat treatment upon the nutritive value of full-fat soybeans was studied in two digestibility and nitrogen balance experiments with sheep, one growth experiment with sheep and two growth experiments with rats. The soybeans were autoclaved for 0 to 90 min. at 121° C. and 1.05 kg./cm.2 of steam pressure. Protein and ether extract digestibility tended to be similar for all soybean diets regardless of length of heating time. The digestibility of the total organic matter and cellulose in the diet was significantly (P<.05) reduced by increased heating time of the soybeans. This reduction appeared to parallel a decrease in the in vitro solubility of the nitrogen in the heated soybeans. In one of the two experiments, urinary nitrogen was reduced and net nitrogen utilization was significantly (P<.05) improved by heating. In the growth study with sheep, there was a significant linear increase in average daily gains as the heating time for the soybeans increased from 0 to 30 minutes. The rat growth studies indicated a significant (P<.01) improvement in rate of gain, feed conversion and protein conversion when soybeans were heated for 15 minutes. Extending the heating time beyond this reduced the nutritive value of the soybeans for rats.