Effects of retrogradation and further acetylation on the digestibility and physicochemical properties of purple sweet potato flour and starch

Abstract

Purple sweet potato flour and starch were treated by retrogradation and further acetylation. The digestibility, physicochemical, and morphological properties of native (NF and NS), retrograded (RF and RS), and acetylated retrograded (ARF and ARS) purple sweet potato flour and starch were investigated. The resistant starch content of RF, ARF, RS, and ARS were significantly increased to 18.72, 25.02, 37.24, and 48.02%, respectively. The soluble dietary fiber (SDF) and total dietary fiber (TDF) of RF and ARF were significantly increased from 10.51 and 27.67% to 20.72 and 40.45%, respectively. Compared with NF and NS, the water soluble index (WSI) of RF and NS were decreased after retrogradation, but increased by the further acetylation. On the contrary, both of retrogradation and further acetylation lead to the decreasing of water absorption index (WAI) and swelling capacity (SWC). The digestion resistibility, retrogradation degree, and particle size of RF, ARF, RS, and ARS were also significantly increased. After heating, the digestion resistibility of NF, RF, NS, and RS significantly decreased, although that of ARF and ARS was not changed obviously. The SEM images showed that the starch particles were melted and aggregated with each other and other components, and their particles became bigger and more compact. Furthermore, further acetylation dramatically decreased the viscosity of retrograded flour and starch.