Cystine and Methionine Metabolism by Chicks Receiving Raw or Autoclaved Soybean Oil Meal

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Abstract
Mild autoclaving, or steaming (100°C. for 30 minutes), of a raw soybean oil meal increased the percentage of the cystine and methionine present in the meal that was retained or metabolized by the growing chick. Steaming apparently increased the digestibility of the soybean oil meal proteins, probably by a destruction of the trypsin inhibitor. More drastic autoclaving (130°C. for 60 minutes) of a raw soybean oil meal reduced the percentage of the cystine and methionine present in the meal that was retained or metabolized as compared to the steamed meal. Retention of supplemental L-cystine by the chicks fed the drastically autoclaved soybean oil meal was the same as that for the chicks fed the raw meal. Retention of the supplemental DL-methionine was, however, decreased from 56% of the intake for chicks fed the raw meal to 20% for those fed the drastically autoclaved meal, and supplemental methionine excretion was increased from 3% to 26%. The formation, by drastic autoclaving, of a substance in the soybean oil meal which interfered with normal digestion and metabolism of methionine is indicated. The addition of supplemental L-lysine to the diet did not affect the cystine and methionine metabolism. Autoclaving did not influence the methionine content of soybean oil meal as determined microbiologically. Drastic autoclaving destroyed 40% of the cystine as shown by a similar assay. The liberation of methionine from soybean oil meal by in vitro digestion with trypsin and erepsin was increased by steaming but again decreased by drastic autoclaving. The drastic autoclaving procedure reduced the nutritive value of soybean oil meal by (1) a partial destruction of cystine and lysine, (2) a decreased digestibility of the lysine not destroyed, and (3) a decreased absorption and utilization of the methionine, probably caused by the formation of a substance which interfered with normal digestion and metabolism of methionine.