The metabolism of alcohols by apple fruit tissue

Abstract

Abstract The interconversion of short‐chain aliphatic alcohols, aldehydes and esters by apple fruit has been studied by gas‐liquid chromatographic analysis of the products when substrates (mainly alcohols) were supplied as vapours to fruit slices at 20°C, and to whole fruit during storage at 3°C. In preliminary experiments with fruit from various sources after different periods of storage, cortical tissue slices formed corresponding aldehydes and acetate esters from alcohols; esterification was more rapid with higher alcohols. Esterification by peel tissue slices was more rapid initially but quickly declined. Metabolism was further investigated with a batch of apples during storage under different conditions. Both cortex and peel tissue were capable of acetylating butanol and 2‐methyl propanol at all stages of maturity, from the pre‐climacteric state at normal harvest time, when endogenous ester levels were low, through 58 days ripening at 12°C. The tissues showed constant hydrolytic activity towards butyl acetate throughout this period. Whole apples in air and 2% O 2 at 3°C took up ethanol but formed little ethyl acetate and retained very little free ethanol. In both atmospheres whole apples metabolised approximately 40% of added hexanol to hexyl acetate and up to 8% to hexanal. The low levels of esters in apples from low oxygen atmospheres (and the absence of esters in unripe apples) are, therefore, a consequence of low rates of alcohol synthesis.