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SUMMARY Isolation and characterization of 7 sorts of diffusable bitter peptides in peptic hydrolyzate of soybean protein were presented. One liter of dilute HCI solution containing 25 g of soybean cold‐insoluble protein and 250 mg of pepsin was incubated at 37°C for 24 hr. The resulting peptic hydrolyzate was dialyzed against water and the diffusable fraction was, after being concentrated at 40°C, investigated by gel permeation chromatography using Sephadex G‐10, ionexchange chromatography of Dowex 50 (w)‐X2 (pyridinium) and thin‐layer chromatography with silica gel G. Bitterness of the diffusable fraction was attributable to free amino acids having bitter flavor, such as isoleucine, leucine, phenylalanine and valine; also to peptides such as H. Gly‐Leu. OH, H. Leu‐Phe. OH, H. Ser‐Lys‐Gly‐Leu . OH, H‐Leu‐Lys . OH, H. Phe‐(lle, Leu 2 )‐ Gin‐Gly‐Val . OH, H. Arg‐Leu‐Leu . OH and H. Arg‐Leu . OH. It was characteristic that almost all diffusable bitter peptides investigated here had leucine at the termini. Through carboxypeptidase A treatment on these peptides, the bitterness decreased considerably. Furthermore, applying carboxypeptidase A or Nagane, a bacterial neutral proteinase, to the diffusable fraction of the peptic hydrolyzate was also effective in removing the bitterness somewhat.
Fujimaki et al. (Fri,) studied this question.