Amylopectin chain length distributions and amylose content are determinants of viscoelasticity and digestibility differences in mung bean starch and proso millet starch

Abstract

This study aimed to reveal the underlying mechanisms of the differences in viscoelasticity and digestibility between mung bean starch (MBS) and proso millet starch (PMS) from the viewpoint of starch fine molecular structure. The contents of amylopectin B2 chains (14.94–15.09 %), amylopectin B3 chains (14.48–15.07 %) and amylose long chains (183.55–198.84) in MBS were significantly higher than PMS (10.45–10.76 %, 12.48–14.07 % and 70.59–88.03, respectively). MBS with higher amylose content (AC, 28.45–31.80 %) not only exhibited a lower weight-average molar mass (91,750.65–128,120.44 kDa) and R1047/1022 (1.1520–1.1904), but also was significantly lower than PMS in relative crystallinity (15.22–23.18 %, p < 0.05). MBS displayed a higher storage modulus (G′) and loss modulus (G′′) than PMS. Although only MBS-1 showed two distinct and discontinuous phases, MBS exhibited a higher resistant starch (RS) content than PMS (31.63–39.23 %), with MBS-3 having the highest RS content (56.15 %). Correlation analysis suggested that the amylopectin chain length distributions and AC played an important role in affecting the crystal structure, viscoelastic properties and in vitro starch digestibility of MBS and PMS. These results will provide a theoretical and scientific basis for the development of starch science and industrial production of low glycemic index starchy food.