Postharvest storage of purple sweetcorn: changes in anthocyanin and sugar content during ambient and refrigerated storage

Sweetcorn (Zea mays var. rugosa) is very closely related to starchy maize (Zea mays var. indentata), with the major genetic difference being a supersweet mutation, such as brittle1 or shrunken2. These mutations reduce conversion of sugar to starch, both as kernels mature on the plant, and during postharvest storage. In contrast to maize, sweetcorn is harvested when kernels are tender and physiologically immature. Consequently, sweetcorn is actively respiring when it is harvested, with sugar being utilised as a substrate for metabolism. Reducing respiration rate during postharvest storage subsequently minimises sugar loss and maintains kernel sweetness. Although most sweetcorn is yellow or white, we have recently developed purple sweetcorn by the inclusion of an active anthocyanin biosynthesis pathway. Anthocyanin is not only responsible for the purple colour, but has also been associated with a number of health benefits. As this product is novel, there is currently no information on changes in anthocyanin or sugar concentration during postharvest storage. The current study reports the effect of common domestic storage temperature (4 °C) and ambient temperature (23 °C) on these key quality characteristics of purple sweetcorn over a two-week period. Storage of purple sweetcorn for 14 days at room temperature significantly increased (P<0.05) kernel anthocyanin concentration from 51 mg/100g FW at day 0 to 99 mg/100g FW, and decreased sugar concentration from 128 mg/g FW to 30 mg/g FW. By contrast, at 4 °C, no significant change in anthocyanin concentration was observed, and the rate of decline in sugar concentration was significantly reduced, declining to only 113 mg/g FW after 14 days. In general, although storage at ambient temperature can induce a significant increase in anthocyanin concentration in purple sweetcorn, this would have to be manipulated carefully so as not to cause a decline in sugars that would significantly affect flavour.