Stimulation of coloration and carotenoid biosynthesis during postharvest storage of ‘Navelina’ orange fruit at 12°C

The effect of storage temperature on color, carotenoid content and composition, and the expression of key carotenoid biosynthetic genes in fruit of 'Navelina' orange were evaluated. Fruit were harvested at two maturation stages, before color break (breaker stage) and with a light-orange coloration (colored), and stored at 2 and 12 °C and 90–95% RH for up to 7 weeks. At the two maturation stages, storage at 12 °C considerably increased total carotenoid content and enhanced coloration in both flavedo and pulp. In fruit stored at 2 °C, coloration and carotenoid content remained almost unchanged. The increase in peel color during storage at 12 °C was mainly related to an increment in the concentration of the reddish C30-apocarotenoid, β-citraurin, and to a minor extent to antheraxanthin. The content of β-cryptoxanthin, a β,β-xanthophyll with pro-vitamin A activity, increased two and three times in the pulp of breaker and colored fruit, respectively, after 7 weeks of storage at 12 °C. The expression of the genes PSY (phytoene synthase), PDS (phytoene desaturase), ZDS (ζ-carotene desaturase), βLCY1 and βLCY2 (β-lycopene cyclase 1 and 2) and βCHX (β-carotene hydroxylase) increased during storage at 12 °C in the peel of fruit at both maturation stages. At 2 °C, by contrast, expression of these genes was maintained or slightly declined. The pattern of changes in gene expression in the pulp of orange fruit stored at 12 °C was dependent of the ripening stage and not always related to the increment in carotenoid content and composition. Collectively, these results indicate that the stimulation of carotenoid biosynthesis during storage of 'Navelina' orange fruit at 12 °C improve not only peel and pulp coloration, but also pro-vitamin A activity of the flesh, and may then be a postharvest strategy to increase the nutritional and health-related benefits of citrus fruit.