Effects of processing on antinutritional factors in legumes: the soybean case

The author recounts his personal trail of research which has ultimately led to better understanding of the factors which contribute to the poor nutritive value of unheated soybeans. Among the techniques that were employed were the isolation of a lectin from raw soybeans, the use of affinity chromatography to remove the trypsin inhibitors, and the nutritional evaluation of soybean varieties which lacked the lectin or the Kunitz trypsin inhibitor. Based on a consideration of the results obtained by these experiments, it was estimated that the trypsin inhibitors accounted for approximately 40% of the growth inhibition on raw soy, of which two-thirds could be attributed to the Kunitz inhibitor and one-third to the Bowman-Birk inhibitor. The soybean agglutinin was deemed responsible for 50% of the inhibition of growth, and the remaining 10% is most likely due to the poor digestibility of the undenatured protein.