Chemical structure and physical properties of mung bean starches isolated from 5 domestic cultivars.

Chemical structure and physical properties of starches isolated from 5 domestic mung bean cultivars (Gyungsun, Geumsung, Sunhwa, Eohul, and Jangan) were examined. The granules were jelly bean like in shape and smooth on surface, and the size was within 10 to 30 microm. Mung bean starches displayed a C(A)-type crystalline structure when judged by the X-ray diffraction patterns. Branch chain-length distribution patterns of amylopectin (AP) revealed that peak chain length of APs was at either DP (degree of polymerization) 12 or DP13. Apparent amylose contents of 5 cultivars by iodine affinity test were 31.7% to 33.8%. Mung bean APs showed a unique molecular size distribution that has not been observed from other plant-derived starches. Two distinct peaks of AP fraction were identified on the size-exclusion chromatogram, and the ratios of these 2 peaks were different depending on the mung bean cultivars. Weight-average chain length (CL(avg)) of APs was in the range of 16.9 (Eohul) and 17.5 (Geumsung). The onset temperature (T(o)) and enthalpy change (DeltaH(gel)) of starch gelatinization were 54.6 to 60.2 degrees C and 11.6 to 13.2 J/g. The DeltaH of the retrograded mung bean starches was 5.5 to 6.6 J/g, which indicated 44.5% to 52.7% of recrystallization. The pasting temperature, peak viscosity, and setback were 66.1 to 69.2 degrees C, 510 to 579 Rapid Visco Unit (RVU), and 66 to 90 RVU, respectively.

Effects of glycerol and moisture gradient on thermomechanical properties of white bread.

The thermomechanical properties of breadcrumb were investigated using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). The main transition (T(1), near 0 degrees C) shifted to lower temperature with added glycerol due to freezing point depression. The low-temperature transition (T(3), approximately -50 degrees C), found only in high-glycerol (8.8%) bread, suggested that of excess or phase-separated glycerol. The high-temperature transition (T(2), 60-85 degrees C) appeared only in aged breadcrumbs; its temperature range was correlated well with the amylopectin melting transition (DSC) but its tan delta amplitude did not correlate well with the amylopectin melting enthalpy (r(2) = 0.72). On the other hand, the change of E' ' (viscous behavior) suggested that T(2) might be related to the change in the amorphous region. Domain-to-domain (amorphous) and crumb-to-crust moisture migrations are two critical phenomenological changes associated with aging and could lead to significant local dehydration of some amorphous regions contributing to mechanical firming during storage.