Cereal Chem 69:178-181   |  VIEW ARTICLE

Effects of Cooking and Treatment with Sodium Bisulfite on In Vitro Protein Digestibility and Microstructure of Sorghum Flour.

D. L. Rom, J. M. Shull, A. Chandrashekar, and A. W. Kirleis. Copyright 1992 by the American Association of Cereal Chemists, Inc. 

The predominant indigestible proteins in cooked sorghum are kafirins, which are stored in protein bodies. In vitro pepsin digestion assay and scanning electron microscopy were used to examine the effects of cooking and treatment with sodium bisulfite on protein digestibility and protein body microstructure. In vitro pepsin digestion assay showed that sorghum decreases in protein digestibility after cooking. Treatment with sodium bisuilfite increased the digestibilities of both cooked and uncooked flour. Scanning electron micrographs revealed that in all treatments the protein matrix is digested before the protein bodies. Protein bodies in uncooked samples were digested by pitting from the outer surface. In contrast, the protein bodies from the cooked sorghum did not exhibit any pitting. They did, however, become ellipsoidal. Cooking changed the protein bodies so that they could not be digested as they had before cooking. Protein bodies in cooked samples that had been soaked in sodium bisulfite did exhbit shallow pits, suggesting a reversal in the reactions that took place during cooking. Since sodium bisulfite prevents the formation of disulfide bonds during cooking and makes the sorghum more pepsin-digestible, formation of disulfide bonds is probably responsible for reduced protein digestibility in cooked sorghum.