Heat treatments increase sweetness and flesh colour of buttercup squash

Buttercup squash (Cucurbita maxima Duchesne 'Delica') fruit were heated to 30 or 33 degrees C in air for up to 7 days, then stored at 12 degrees C for up to 7 weeks. Control fruit remained at 12 degrees C throughout. Sucrose and starch concentrations were measured in edible portions of raw squash, and the perceived sweetness of the cooked fruit was evaluated using a trained sensory panel. Enzymes of starch degradation and sucrose metabolism were also extracted and assayed. Sucrose content, on a dry weight basis, was as much as 250% higher in heat-treated fruit than in fruit kept at 12 degrees C. Sucrose accumulated with increasing length of treatment and continued to accumulate during subsequent storage. There was a strong correlation between sucrose content and panel sweetness rating. Heat treatments also increased the red/ yellow colour of the flesh. Both increased sucrose concentration and redder flesh colour appear to increase the acceptability of buttercup squash to consumers. In a subsequent experiment, we found that extractable activities of a-amylase, P-amylase, starch phosphorylase, D-enzyme, sucrose synthase, sucrose phosphate synthase, maltase, and maltose phosphorylase did not differ in samples taken from heat-treated or non-heat-treated squash.