Carotenol esters in developing apple fruits

Abstract

The carotenol esters of apple (Malus pumila, cv Cox's Orange Pippin) fruit peel were partially characterized, and their accumulation measured relative to changes in ethylene concentration. Monoesters of violaxanthin, neoxanthin and an unknown pigment, possibly cryptoxanthin 5,6,5′,6′-epoxide, were found. Lutein, violaxanthin and neoxanthin were present as diesters. Palmitate and oleate were the main acyl substituents, with lesser amounts of laurate, myristate and stearate. There were large families of diesters, presumably including mixed fatty acyl derivatives, and these were not fully resolved by reverse phase HPLC. The pattern of acyl substitution appeared to recur among the mono- and diesters of the different carotenols. Violaxanthin mono-oleate and palmitate began to accumulate ca 20 days before the rise in ethylene production associated with fruit ripening, whereas the increase in the corresponding diesters was concurrent with the rise in ethylene. The results suggest that carotenol esters are synthesized de novo in ripening apples and that synthesis may be independent of ethylene or require lower concentrations to initiate than other ripening processes. The pigments could serve as early indicators of fruit maturity.