Starch Degradation in Buttercup Squash (Cucurbita maxima)

Extractable activities of α-amylase, β-amylase, and starch phosphorylase were investigated in order to understand the mechanism of starch degradation in buttercup squash ( Cucurbita maxima Duchesne ex Lam. `Delica') with the ultimate goal of improving the conversion of starch into sweet sugars. During rapid starch synthesis (0 to 30 days after flowering), extractable activities of α-amylase and β-amylase were low, but those of starch phosphorylase increased. After harvest, during ripening at 12 °C, or in fruit left in the field, activities of α-amylase and β-amylase increased. Starch contained 20% to 25% amylose soon after starch synthesis was initiated and until 49 days after harvest irrespective of whether the crop remained in the field or in storage at 12 °C. Maltose concentrations were low prior to harvest, but levels increased during fruit ripening. Data suggest starch breakdown is hydrolytic in buttercup squash, with α-amylase being the primary enzyme responsible for initiating starch breakdown.