The Nutritive Quality and the Trypsin Inhibitor Content of Soybean Flour Heated at Various Temperatures

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Abstract
A method was developed for determining the trypsin inhibitor potency of raw or heated soybean flours. The protein efficiency of soybean flour increased in direct proportion to the destruction of its trypsin inhibitor potency by heat. The protein efficiencies of autoclaved soybean flour to which the inhibitor had been added, and of isolated soybean protein partially freed of the inhibitor, agreed well with the values predicted from the results with heated flours. It was concluded that the presence of the trypsin inhibitor was the chief cause of the poor utilization of the protein or of inadequately heated soybean flours. Autoclaving at 108°C. for 15 to 30 minutes produced a soybean flour of optimal protein efficiency for mice, while autoclaving at 120°C. for 5 or 10 minutes resulted in a slightly poorer product. Autoclaving for periods of over 10 minutes at 120°C. caused a progressive decrease in the protein efficiency of the flour. On the basis of this evidence, it is suggested that the determination of the inhibitor potency of soybean products may be used as a practical index of the effectiveness of the heating to increase the protein quality, providing that the heating is not continued beyond the time required for the total destruction of the inhibitor.