Ester Production and Alcohol Acyltransferase Activity in Fresh-cut Melon during Storage

Changes in volatile ester production and alcohol acyltransferase (AAT) activity of fresh-cut Japanese muskmelon varieties during storage were investigated. Green fleshed “Andes”, “Arus”,and “Takami” and orange fleshed “Northland red” were cut into approximately 3×3cm pieces, placed in a plastic box and stored at 4°Cand 8°C for 3 days. Production of volatile aroma compounds during storage was determined by gas chromatography using head-space (HS) and solid-phase microextraction (SPME) methods. AAT activity of fresh-cut melons with storage was also determined. Ethyl acetate, isobutyl acetate, isoamyl acetate, and hexyl acetate were detected as predominant aliphatic esters in Andes, Arus and Northland red melons. Those esters except ethyl acetate were isolated as predominant esters from Takami melon on day 0 and day 1, while only a slight amount of ethyl acetate production was detected on day 2. Melon samples, which were stored at 8°C showed higher amount of ethyl acetate production than those stored at 4°C. Production of ethyl acetate in Andes and Arus melons was moderately increased on day 1 and then decreased maybe due to cutting stress. The optimum pH activity of AAT from Arus melon was observed at pH 8. The enzyme extracted from Arus melon showed higher substrate specificity for butyl alcohol, isobutyl alcohol, isoamyl alcohol and hexyl alcohol and lower affinity for methyl alcohol and ethyl alcohol. During storage, AAT activity of Takami melon changed from 0.056 µmol.gfw^-1.h^-1 on day 0 to 0.0381 and 0.0359 µmol.gfw^-1.h^-1 on day 2 at 4ºC and 8 ºC respectively. The results from our research concluded that fresh-cut Takami melon produced very little amount of ethyl acetate compared with that of other varieties used in this study and AAT activity of the melon was slightly decreased during storage.