17C-13 |
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H. D. WOO1, S. J. Choi1, H. J. Ha1, B. R. Hamaker2, and T. W. Moon1. (1) Department of Food Science and Technology, Seoul National University, School of Agricultural Biotechnology, San 56-1, Shillim-dong, Kwanak-gu, Seoul, 151-742, South Korea, (2) Whistler Center for Carbohydrate Research, Purdue Univ., Dept. of Food Science, 745 Agriculture Mall Dr., West Lafayette, IN 47907-2009 Grain sorghum shows lower protein digestibility and starch digestibility compared with other cereal grains. Low sorghum protein digestibility by pepsin is due to resistance of kafirins, the major storage protein constituting the protein body and matrix with many intra- and inter-disulfide bonds. Low starch digestibility has been suggested to be due to the restrictions in accessibility to starch caused by protein body and matrix. Reducing agent can break the disulfide bonds and make sorghum protein more digestible. However, few studies have been reported in which enzyme digestion was carried out in the presence of a reducing agent. The objective of this study was to investigate in vitro digestibility of sorghum protein and starch in the presence of sodium bisulfite, a food-grade reductant. Sorghum flours were soaked for 12 hours at 0-10 mM concentration of sodium bisulfite. Flours were digested by pepsin with sodium bisulfite for 120 min. After pepsin digestion, digested protein was discarded and undigested protein was extracted with 0.0125 M sodium tetraborate buffer. In vitro protein digestibility of sorghum flours was determined by measuring the turbidity of undigested protein extracts with 72% TCA at 562 nm. For in vitro starch digestibility, sorghum flours were digested by a-amylase and amyloglucosidase with sodium bisulfite for 120 min. After digestion, concentration of free reducing sugar was measured by the Nelson-Somogyi method. Increase in sodium bisulfite concentration decreased the amount of undigested protein by pepsin, implying that sodium bisulfite treatment made sorghum protein body and matrix more digestible. Starch digestibility of sorghum flours treated with sodium bisulfite was higher than that of untreated flours. As the concentration of sodium bisulfite increased, starch digestibility increased. These results suggest that sodium bisulfite, which makes starch easily accessible to enzymes, could be used to control the starch digestibility of sorghum flours.
Session 17C, Food Chemistry: Cereals, grains, legumes and their products
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