Resistant starch formation and changes in physicochemical properties of waxy and non-waxy rice starches by autoclaving-cooling treatment

Abstract

ABSTRACT Resistant starch (RS) has drawn great attention from both starch research and industrial communities due to its potential health benefits. Physical starch modification approach, such as autoclaving and cooling cycle treatment, offers high potential method of enhancing resistant starch fraction due to its simplicity and cost-effectiveness. Here, the non-waxy KDML105 and waxy RD6 rice starches were physically modified by one, three, and five autoclaving and cooling cycles. The comparative impacts of the modification on the RS content and starch physicochemical properties were examined. Their native starch granules were transformed into a larger continuous matrix with suppressed thermal and pasting properties. However, modified KDML105 starch gels with higher amylose content and the presence of amylose lipid complexes were able to retrograde and maintain viscosity better than the modified RD6 starch. The RS content was also increased with the addition of treatment cycles in KDML105 starch. As a result, the RS content of native KDML105 starch was enhanced from 0.13% to 2.59% after five cycles of the treatment. The dissimilarities observed between the two modified starches could be due to the different degrees of increased proportions of ordered (R1047/1022) and double helical (R995/1022) structures, and the disruption of A- and V-type crystals. Therefore, the RS content was attributed to an interplay of alterations in ordered structure, amylose, and amylose-lipid complex during autoclaving-cooling cycles.