Two genes (CM-AAT1 and CM-AAT2) with strong sequence homology (87% identity at the protein level) putatively involved in the formation of aroma volatile esters have been isolated from Charentais melon fruit. They belong to a large and highly divergent family of multifunctional plant acyl-transferases and show at most 21% identity to the only other fruit acyl-transferase characterized so far in strawberry. RT-PCR studies indicated that both genes were specifically expressed in fruit at increasing rates in the early and mid phases of ripening. Expression was severely reduced in ethylene-suppressed antisense ACC oxidase (AS) fruit and in wild-type (WT) fruit treated with the ethylene antagonist 1-MCP. Cloning of the two genes in yeast revealed that the CM-AAT1 protein exhibited alcohol acyl-transferase activity while no such activity could be detected for CM-AAT2 despite the strong homology between the two sequences. CM-AAT1 was capable of producing esters from a wide range of combinations of alcohols and acyl-CoAs. The higher the carbon chain of aliphatic alcohols, the higher the activity. Branched alcohols were esterified at differential rates depending on the position of the methyl group and the nature of the acyl donor. Phenyl and benzoyl alcohols were also good substrates, but activity varied with the position and size of the aromatic residue. The cis/trans configuration influenced activity either positively (2-hexenol) or negatively (3-hexenol). Because ripening melons evolve the whole range of esters generated by the recombinant CM-AAT1 protein, we conclude that CM-AAT1 plays a major role in aroma volatiles formation in the melon.

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The effect of natural coating by using fresh Aloe vera (A. vera) gel alleviating browning of fresh-cut wax apple fruits cv. Taaptimjaan was investigated. The fresh-cut fruits were dipped in fresh A. vera gel at various concentrations of 0, 25, 75 or 100 % (v/v) for 2 min at 4 ± 1 °C for 6 days. Lightness (L*), whiteness index (WI), browning index (BI), total color difference (ΔE*), sensorial quality attributes, total phenolic (TP) content, antioxidant activity and polyphenol oxidase (PPO) and peroxidase (POD) activities were determined. During storage, L* and WI of the fresh-cut fruits surface decreased whilst their BI and ΔE* increased. A. vera coating maintained the L* and WI and delayed the increase in BI and ΔE*, especially at 75 % A. vera dip. The fresh-cut fruits dipped in 75 % A. vera had the lowest browning score, the highest acceptance score and delayed the increase in TP content and PPO activity. However POD activity was induced by A. vera coating. Antioxidant activity had no effect on browning incidence of the fresh-cut fruits. Consequently, A. vera gel coating could maintain quality and retarded browning of fresh-cut wax apple fruits during storage.

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