The objectives of this study were 1) to investigate the effect of enzymatic treatment (pullulanase concentration and hydrolysis time) on physicochemical properties of modified rice starch, 2) to evaluate the effects of enzymatic modification on the ra ...
The objectives of this study were 1) to investigate the effect of enzymatic treatment (pullulanase concentration and hydrolysis time) on physicochemical properties of modified rice starch, 2) to evaluate the effects of enzymatic modification on the rate and extent of starch digestion, 3) to determine and compare the ratio of the major starch fractions [rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS)] using different analytical in vitro methods (GOPOD vs. DNS method), and 4) to investigate the optimal conditions for producing SDS and RS and compare physicochemical properties and physiological functions of optimized SDS and RS. Rice starch was treated with different concentrations of enzyme and hydrolysis times. As hydrolysis time and enzyme concentration increased, the fraction of RDS decreased (78.31→44.65%), whereas SDS (0.8→22.18%) and RS (20.79→34.43%) increased. As enzyme concentration increased, in vitro starch digestibility (ISVD) decreased in all hydrolysis time. Swelling factor (SF), water absorption index (WAI), and water solubility index (WSI) significantly decreased, while syneresis and turbidity increased as the concentration of enzyme increased in all hydrolysis time. Pasting properties of enzyme-treated rice starch decreased with increasing amount of pullulanase, regardless of hydrolysis time. The X-ray diffraction of enzyme-treated rice starch showed A-type and a weak V-type pattern. Optimum conditions for production of SDS and RS were determined by response surface methodology (RSM) and determination of starch fraction (RDS, SDS, and RS) was evaluated using GOPOD and DNS method. Also, physicochemical properties and response in mice of optimized SDS and RS were investigated in comparison with native rice starch. Using GOPOD method, the optimum conditions for SDS fraction were obtained at the [pullulanse concetration, X1] of 482 μL, [storage temperature, X2] of 36°C, and [A-C cycle, X3] of 3, and for RS fraction, were determined to be 610 μL (X1), 63°C (X2), and cycle of 3 (X3). Amylose content of SDS and RS significantly increased in comparison to native rice starch (p<0.05). For SDS and RS fractions, WAI was increased, SF, WAI, and oil binding were decreased compared to native rice starch. During the freeze-thaw cycles, the native rice starch gel showed significantly lower syneresis than did SDS and RS gels. The turbidity values of SDS and RS fraction were higher than native rice starch. The extent of hydrolysis with α-amylse followed the order: cooked (67.84%) > SDS (53.21%) > RS (44.80%) > Native rice starch (12.94%). Pasting curves of SDS and RS were flat and paste viscosity showed a drastic reduction. The granule morphology of SDS and RS showed disrupted granular form, and bigger, irregularly shaped particles as compared to native rice starch. Using DNS method, the optimum conditions for SDS fraction were obtained at the [pullulanse concentration, X1] of 498 μL, [storage temperature, X2] of 47°C, and [A-C cycle, X3] of 5, and for RS fraction, were determined to be 838 μL (X1), 62°C (X2), and cycle of 3 (X3). The body weight gain did not differ among the groups. In rice treatment groups (Rice-Native, Rice-SDS, and Rice-RS) perirenal fat weight significantly decreased compared to the high-fat control group(p<0.05). Rice-RS and Rice-Native groups significantly lower serum lipid and cholesterol concentrations(p<0.05). The serum triglyceride levels were significantly lower in mice fed Rice-SDS and Rice-RS group(p<0.05). The total liver cholesterol decreased significantly in rice treatment groups (Rice-Native, Rice-SDS, and Rice-RS)(p<0.05). The total liver cholesterol lowering effect was observed in Rice-RS group. The total lipid content and triglyceride in fecal significantly increased in Rice-SDS group(p<0.05). The total fecal cholesterol in mice fed both Rice-SDS and Rice-RS were significantly higher than in all other groups.