Uncovering the multiscale structure and physicochemical properties of starch extracted from naturally fermented mung bean liquid by wet milling

In this study, mung bean liquid (MBL) was prepared by wet milling and then naturally fermented for 0, 24, 48, 72, and 96 h. Afterward, the starch extracted from MBL was analyzed. The pH of MBL decreases from 6.54 to 4.91 during fermentation. Moreover, the mung bean starch (MBS) granules changed significantly with pitted surfaces, pores and channels. The particle size, molecular weight (Mw) and long chain amylopectin (B2) content of the MBS decreased, whereas the short chain (A) increased from 20.57% to 22.70% with increasing fermentation time. Natural fermentation had no effect on the crystalline type (A) of the MBS but increased the relative crystallinity from 26.53% to 29.23%. However, the intensity ratios of the 995/1022 cm-1 and 1047/1022 cm-1 FTIR spectra increased with fermentation time, reaching maxima of 0.95 and 0.80 after 48 h, respectively. In addition, Fermented MBS increased the trough viscosity (TV), final viscosity (FV), elastic modulus (G ') and viscous modulus (G '') but decreased the peak viscosity (PV) and breakdown (BD). Thermal properties revealed that fermentation increased the gelatinization enthalpy (Delta H) from 9.49 to 10.26 J/g.