Development of Isoamyl Acetate Biosynthetic Pathway in Banana Fruit during Ripening and Suppression of Its Development at High Temperature

Abstract

Banana (Musa sapientum L.) fruit ripened at 20°C and 30°C produced a large quantity of volatile compounds including isoamyl acetate, however, the production was extremely suppressed in the fruit ripened at 35°C. The contents of L-leucine, α-ketoglutarate, isoamyl alcohol, acetic acid, ATP and CoA which were considered as the metabolites or co-factors of assumed isoamyl acetate biosynthetic pathway in the fruit, were determined during ripening at 20°C, 30°C and 35°C. ATP content in the fruit decreased during ripening at all temperatures, but the other compounds increased at 20°C and 30°C. At 35°C, however, these compounds decreased except α-ketoglutarate and acetic acid. The activities of the enzymes which were thought to catalize isoamyl acetate biosynthesis, that is, leucine transaminase, α-ketoisocaproate decarboxylase, alcohol dehydrogenase, acetyl CoA synthetase and acyl CoA-alcohol transacylase increased during ripening at 20°C and 30°C, but the activation was prevented at 35°C. Among the enzymes mentioned above, α-ketoisocaproate decarboxylase and acyl CoA-alcohol transacylase were not detected in mature-green stage, suggesting that the appearance of these two enzymes would play most important role in the development of isoamyl acetate biosynthetic pathway in ripening banana fruit. In addition, the activation of other enzymes and increases of substrate contents in the pathway are also supposed to contribute the production of isoamyl acetate. It may be concluded that the postulated pathway of isoamyl acetate biosynthesis develops in banana fruit during ripening, while it must be suppressed at 35°C in storage temperature.