Structural and physicochemical properties of mung bean starch as affected by repeated and continuous annealing and their in vitro digestibility

Mung bean starch slurries (75% moisture) were respectively treated by repeated annealing (RANN) at 50 degrees C for eight repetitions (every repetition was treated for 12 h) and continuous annealing (CANN) at the same temperature for 24, 48, 72 and 96 h. After RANN and CANN modifications, variations in the physicochemical properties, structures as well as digestive characteristics of mung bean starch were investigated. Scanning electron microscopy observed the grooves on the surfaces of starch granules became deeper after RANN and CANN modifications, and the cracks in the granule centers were monitored by light microscopy. However, there was no distinct change detected by confocal laser scanning microscopy. RANN and CANN modifications increased the crystallinity and degree of crystalline order, but the crystalline patterns were not changed. Under the same annealing time, RANN samples presented higher crystallinity, gelatinization temperature, enthalpy, peak time, pasting temperature, resistant starch (RS), slowly digestible starch (SDS) and SDS+RS values, but lower solubility, swelling power, peak viscosity, breakdown and rapidly digestible starch (RDS) values than CANN samples. Therefore, RANN could exert conspicuous impacts compared to CANN, which illustrates the annealing impact on starch modification and it could be applied in food processing as an innovative approach.