Starch and Protein digestibility of novel extruded binary blended foods.
M. JOSEPH (1), L. Zhu (1), Q. Guo (1), B. Lindshield (2), S. Alavi (1). (1) Department of Grain Science and Industry, Kansas State University, Manhattan, KS, U.S.A.; (2) Department of Human Nutrition, Kansas State University, Manhattan, KS, U.S.A.
Starch and protein digestibility of novel protein-rich fortified blended foods (FBFs) designed for nutritional interventions, based on binary blends of sorghum-cowpea (SCB), sorghum-soy (SSB) and corn-soy (CSB), before and after extrusion were studied as digestibility contributes to nutritional and calorific significance of ingested food. Starch and protein digestibility was estimated by modified <i>in-vitro </i>Englyst method (1992) and Mertz et al. (1984) respectively. Results showed that extrusion led to enhanced <i>in-vitro </i>total starch digestibility (TDS) in the binary blends. TDS increased by 26.29%, 12.32% and 66.26% for SCB, SSB and CSB, respectively. It also had significantly higher <i>in-vitro </i>rapidly digestible starch (RDS) than non-extruded binary blends, which increased from 12.04% to 42.12%, 15.14% to 46.96% and 8.11% to 48.94% for SCB, SSB and CSB, respectively. In addition, extrusion lowered slow digestible starch (SDS) in all the blends, indicating that some SDS was converted to RDS during extrusion processing. TDS values greater than 100% in extruded and cooked samples may have been due to conversion of some polysaccharides to glucose during extrusion process. However, extrusion showed no substantial effect on protein digestibility of binary blends (86-89% in raw vs 85-88% in extruded). Cooking reduced the protein digestibility from 85.55% to 80.72%, 85.87% to 82.32% and 88.07% to 85.28%, in extruded SCB, SSB and CSB, respectively. A possible interaction of proteins with retrograded starch generated during cooling of cooked binary blends could have reduced the accessibility of the pepsin to protein molecules. Also, the protein agglomeration during cooking in excess water in sorghum based binary blends (SCB and SSB) could lead to decrease in protein digestibility. These protein digestibility values were still higher than cooked control sample CSB13 (60.91%).
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