Preferential accumulation of orange-colored carotenoids in Ponkan (Citrus reticulata) fruit peel following postharvest application of ethylene or ethephon

To avoid winter frost, Ponkan (Citrus reticulata Blanco cv. Ponkan) fruit in Zhejiang Province, China, is frequently harvested early, while chlorophylls are still present in the peel. Postharvest degreening of Ponkan fruit, through either ethylene fumigation or ethephon dipping, was carried out to study the effects of both treatments on color development and carotenoid accumulation. An earlier and deeper orange color development after treatments was indicated by a decline in hue angle (H°) and an increase in the citrus color index (CCI). Total carotenoid content increased, while chlorophyll content decreased during storage at 10 °C, and these changes were accelerated by both treatments. The treatments stimulated preferential accumulation of carotenoids with orange color (β-carotene and β-cryptoxanthin) while reducing the abundance of carotenoids with yellow color (lutein, violaxanthin and 9-cis-violaxanthin). Gene expression of β-carotene hydroxylase (BCH) was inhibited by both treatments, which could be related to the changes in composition of these differently colored carotenoids.