Optimisation of heat-moisture treatment conditions for producing high amounts of resistant starches from purple sweet potato and yam starches using response surface methodology

Abstract

Heat-moisture treatment, a physical modification method of starch, causes changes in the internal structure of starch and thereby produces resistant starch (RS). In this study, the heat-moisture treatment conditions (moisture content, heating temperature, and incubation time) was optimized to maximise the RS contents of the treated sweet potato and yam starches, using the Box-Behnken design and response surface analysis. The predicted maximised RS content of the treated sweet potato starch (43.9%) was obtained under optimal conditions of 34.76% moisture content, heating temperature of 100.11°C, and incubation time of 6.01 h; the predicted maximised RS content of the treated yam starch (36.8%) was obtained under optimal conditions of 30.06% moisture content, heating temperature of 109.68°C, and incubation time of 6.59h using a quadratic model within the range of various process variables. The experimental RS contents of the treated sweet potato and yam starches obtained under optimal treatment conditions were 42.4% and 35.4%, respectively; this confirms that the models were valid and adequate because the predicted data and experiment data did not differ significantly. The results also indicate that the RS contents of the treated sweet potato starch were significantly higher than that of the treated yam starch. As a result, both starch structure and treatment conditions were determined to significantly affect the formation of RS in the heat- moisture treated starches.