Starch Degradation in Buttercup Squash (Cucurbita maxima)

in Journal of the American Society for Horticultural Science
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  • 1 School of Land and Food, University of Queensland, Gatton, Qld 4345, Australia
  • | 2 Food Industry Science Center, New Zealand Institute for Crop and Food Research Ltd, Private Bag 11600 Palmerston North, New Zealand

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.

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