Carotenoid Changes in the ‘Shamouti’ Orange Peel During Chloroplast—Chromoplast Transformation on and off the Tree

Abstract

Seasonal changes in peel carotenoids were investigated in Shamouti oranges on and off the tree. Generally the pattern of changes in carotenoids during the colour transition of the peel from green to orange (colour break) was similar in attached fruit, in fruit detached when still green and stored under normal conditions at 20°C, and in fruit undergoing de-greening by ethylene. There was a gradual disintegration of chloroplasts, as shown by the disappearance of chlorophylls. Total carotenoids reached a minimum level and subsequently began to accumulate. At this point, there was a hypsochromic shift of 6–8 nm in the absorption spectrum of total carotenoids indicating not only the completion of the conversion of chloroplasts to chromoplasts but also the appearance of carotenoids of a different type. The main changes were the disappearance of β-carotene, lutein, and neoxanthin, and the appearance of phytofluene, isomers of violaxanthin, various other epoxides and pink apo-carotenals, and methylketone carotenoids. Phytofluene was found to reach relatively higher concentrations in stored fruit. The observed changes in the composition and amount of carotenoids appear to characterize the transformation of chloroplasts into chromoplasts in both attached and detached green fruit.