Effects of Thermal Pre-treatment on Gelatinization of Starch inside Cotyledon Cells of Adauki Bean

Abstract

In order to clarify the mechanism of gelatinization of starches inside cotyledon cells of adzuki bean (Vigna angularis), gelatinization of starches inside cells and isolated starches heated previously for one hour at a temperature of 60 to 90°C was examined by differential scanning calorimetry (DSC) and birefringence. DSC thermograms of cells showed a endothermic transition with peak temperature at about 70°C which trailed a shoulder up to 98°C. The pre-treatment of cells at 60 and 65°C caused an increase in the onset (To) and peak (T_p) temperatures, and a sharpening of the peak. An increase in T_o and T_p, and a decrease in the gelatinization enthalpy(ΔH) were observed with a further increase in pre-treatment temperature. These changes in the endotherm on a lower temperature side by the pre-treatment were nearly identical to those for isolated starches. The shoulder of the endotherm on a higher temperature side was not affected by the pre-treatment at temperatures below 80°C. The effect of pre-treatment temperature on loss of ΔH agreed with that on loss of birefringence for both starches inside cells and isolated starches. The losses of ΔH and birefringence for starches in side cells were suppressed compared to those for isolated starches by the pre-treatment at 65 to 80°C.