Production of Ethanol and Methanol in Fresh-Cut Fruits at Different Maturity Stages during Storage

Abstract

　Ethanol and methanol levels in fruits are fundamental to the production of fruit aroma. The levels of these chemicals in selected cut-fruits (bananas, pineapples, melons, tomatoes, kiwifruits, and strawberries) were measured immediately after cutting and 24 h after storage at 3℃, at unripe, ripe, and overripe stages. Overripe fruits had higher levels of ethanol and higher ethyl acetate emission than those at the ripe stage, and all of them developed off-flavor, except kiwifruits. The ethanol content in one of the two cultivars of strawberry examined, increased dramatically 24 h after cutting, although it was at a good ripening stage. The methanol and ethanol contents in tomatoes increased sharply and gradually, respectively, after cutting. The strawberries and tomatoes had an unusual aroma 24 h after cutting. Higher alcohol dehydrogenase (ADH) was detected in bananas, pineapples, melons, and kiwifruits. These fruits were shown to have a quick increase in ethanol contents while ripening. The sudden increase in ethanol after cutting or aging of 'Sagahonoka' strawberry could not be explained by ADH activity. The gradual increase in ethanol content in tomatoes may be due to de novo induction of ADH. Tomatoes had very high levels of pectin methyl esterase and were shown to have a quicker increase in methanol levels after cutting. An ability of acetate ester production was detected in all fruits examined, except in kiwifruits. To conclude, the accumulation of ethanol and ethyl esters, especially ethyl acetate, seems to accelerate off-flavor in the overripe stage or during aging. An analysis of ethanol and methanol content of cut fruits over short time duration (2 h) was conducted at room temperature (23℃) using bananas, tomatoes, and strawberries. The changes in alcohol levels were almost the same as those at 24 h after cutting (at 3℃) in bananas. The two cultivars of strawberries used in this experiment showed equal increases in ethanol content at room temperature. This analysis also revealed that ethanol content in strawberries and tomatoes were at negligible levels immediately after cutting, then increased sharply in strawberries, while did so gradually in tomatoes.