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% 0 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.

Ester synthesis by apples supplied with alcohols (C2-CS) and methyl esters of short chain fatty acids (C4-C8) was studied using gas chromatographic analysis of the products. The substrates were supplied as vapours to whole fruits stored in 2% O2 at 3°C. The alcohols were converted to the corresponding acetate ester; butanol, pentanol and hexanol were converted most rapidly. The methyl esters of short chain fatty acids (C,) were converted to esters with an alkyl group (Cn-2, Cn-4) confirming the presence in whole fruits of an active 0-oxidation pathway for fatty acids. Ester synthesis was stimulated when apples were supplied with methyl octanoate at different periods during long term storage in 2% 02. Treatment of the fruit immediately postharvest did not enhance ethylene synthesis.

Cox's Orange Pippin apples gradually lost their capacity to ripen normally when they were stored in 2 % oxygen at 3.5 "C. When the apples were transferred to air at 20 "C, volatiles except ethylene were produced in much smaller amounts than from apples which had been stored in air or 5 % carbon dioxide in air. When Golden Delicious apples were stored with different combinations of temperature and concentrations of oxygen and carbon dioxide, the rate of volatile production, its nature and the total amounts produced after storage were affected. There were residual effects also on the rate of chlorophyll loss and softening.

No abstract

Cox's apples were stored for up to 6 months in the presence or absence of anhydrous calcium chloride in an atmosphere containing 2% 0 2 and < 1% C 0 2 at 3.5"C, and effects on the physical properties of the fruit were assessed for up to 6 months. The desiccant was used to obtain an initial water loss of about 5% of fruit weight in the first 30 days of storage. In control fruit, turgor pressure appeared to be maintained during storage, and fruit volume increased as the air space in the fruit tissue increased. Initial weight loss lowered turgor pressure and prevented this increase. The force required to disrupt slices of apple in the Kramer shear cell was usually higher after initial weight loss, but resistance to the conventional penetrometer was little affected. Initial weight loss led to higher levels of soluble pectin and higher resistance to gaseous diffusion. In sensory tests the high weight-loss fruit was firmer, tougher and less mealy than control fruit.