Influence of microwave treatment conditions and acid concentration on pyrodextrinization of sweet potato (Ipomoea batatas Lam.) starch using response surface methodology

Abstract Microwave irradiation provides advantages including homogeneous and rapid heating, significant reaction acceleration due to heating rate and selective heating. This study aims to optimize the microwave assisted pyrodextrinization of sweet potato ( I. batatas Lam.) starch isolated from tubers grown in Central Africa to produce a yellow pyrodextrin with improved structural and functional properties. The effects irradiation of power (80—100 W), Acid to starch ratio (1.5—3.0 g HCl/kg of starch) and number of cycle/time unit (4—6 cycles with 20 s/cycle) on the response variables were investigated using Response Surface Methodology (RSM). The physicochemical characteristics were also determined on pyrodextrins obtained in optimal conditions by microwave pyroconversion process. The positive interactions were observed between Irradiation power (X 1 ) and Acid to starch ratio (X 2 ) and between Acid to starch ratio (X 2 ) and number of cycle/time unit (X 3 ) for Color index response (P < 0.05). The Acid to starch ratio and its quadratic effect had significant (P < 0.05) influence on saccharification percentage. Th optimal condition for the domain of study were: irradiation power 84 W; Acid to starch ratio of 3.14 g HCl/Kg of starch and number of cycle/time unit of 4.6 for 20 s per cycle. The characteristic of microwave assisted pyrodextrin were: saccharification percentage 92.5%, solubility 98.20%. Its relative crystallinity of 20.97% compared to 26.32% of native starch from XRD and glass transition temperature Tg 144 °C from DSC. The FTIR analysis suggested that of native starch native starch had more short-range order than pyrodextrin. Yellow pyrodextrin with high solubility might be produced in a comparatively short amount of time using microwave assisted treatment.