Gelatinization of Starches inside Cotyledon Cells of Adzuki Bean Studied by Differential Scanning Calorimetry

Tomoko FUJIMURA and Masayuki KUGIMIYA

Abstract

Differential scanning calorimetry (DSC) was used to study the gelatinization of starches inside cotyledon cells of adzuki bean (Vigna angularis) and isolated starches. DSC thermogram of cotyledon cells showed a endothermic transition with peak temperature at about 70°C which trailed a shoulder up to about 98°C, although that of isolated starches showed a single endothermic transition with peak temperature at about 71°C. The transition enthalpy (cal/g starch) for cotyledon cells was nearly equal to that for isolated starches. From these results it was assumed that the endothermic phenomenon at 70°C of cells was ascribed to the starch gelatinzation taken place by the same mechanism as that of isolated starches and the higher temperature transitions were ascribed to the starch gelatinization inside cells at higher temperatures, which suggested that the gelatinization of starches inside cotyledon cells was suppressed. Cotyledon cells were subjected to such treatments with pectolyase or cellulase under appropriate conditions that caused an rupture of cells by swelling of starch granule accompanied by gelatinization of starches inside cells. DSC thermograms and the transition enthalpy (cal/g starch) obtained for the cells previously treated with enzymes were almost the same as those for isolated starches except that a small shoulder was observed at about 75°C. Thermograms for isolated starches were not affected by the addition of adzuki protein. From these results it was assumed that the suppression of gelatinization might be related to the physical strength of cell walls and the limited supply of water required for the gelatinization of starches inside cells.