Extrusion-aided interaction of rice starch with whey protein isolate: Synergistic influence on physicochemical properties and in vitro starch digestibility characteristics.

Synergistic influence of extrusion conditions and whey protein isolate (WPI) incorporation on glycemic response and physicochemical characteristics of rice starch was studied. Box-Behnken Design was used to evaluate effect of process variables (rice starch:WPI ratio; feed moisture and barrel temperature) on quality characteristics of resistant starch-rich, low GI extruded snacks (RSLG-E). Optimum conditions for development of RSLG-E were WPI:18.30 %, feed moisture:20 % and barrel temperature:120 °C. FTIR spectroscopy showed maximum peaks at 1615 cm and 1540 cm corresponding to presence of amide group; however, such band was absent in control. Thermal analysis indicated significantly higher transition temperatures in RSLG-E than control. Expansion ratio (3.79 ± 0.17) and overall acceptability (4.48 ± 0.05) were found to be significantly lower in RSLG-E. In vitro digestibility indicated significantly lower very rapidly digestible starch (2.08 ± 0.03 %) and rapidly digestible starch (68.49 ± 1.07 %) in RSLG-E than control. Digestible starch (86.85 ± 0.97 %), starch hydrolysis rate (58.72 ± 0.97 %) and slowly digestible starch (72.61 ± 0.82 %) were lower in control.