## 3 Discussion
Our results are similar to those reported in previous studies, except hexyl acetate was not detected in our study, and the content of hexanoic acid 3-methylbutyl ester was low, which may be due to many factors, such as different varieties, cultivation conditions, and post-harvest storage conditions [7]. Moreover, different origins of banana varieties have different aromatic compositions and concentrations [14; 21]. Previous work showed that hexyl acetate was the main esters in banana samples (cv. Gran Enano, _Musa_ spp., AAA-genome group), which is originated from three different locations from Central and South America (Costa Rica, Panama and Colombia) [12], and its volatiles production was significantly affected by ethylene treatment. However, for other cultivars such as cvNanicao (_M. acuminata_, AAA, harvested from Sao Paulo State, Brazil) and cv. Prata (_M. acuminata_ X M. balbisiana, AAB, harvested from Minas Gerais State, Brazil), hexyl acetate was not detected or at very low level, and the volatiles vary between those two cultivars and are greatly affected by storage temperature [21]. Similarly, our previous work could not detect or only detected very low level of hexyl acetate in Brazilian banana fruit [13], but high hexyl acetate content was detected in Fenjiao fruit in the present work. Our data also show that the predominant volatile compounds in Fenjiao banana were similar to those of the Brazilian banana at the mature-green stage, such as C\({}_{6}\)-aldehydes, C\({}_{6}\)-alcohols, and abundant esters, especially isoamyl acetate, at the fully ripened stage. The main esters in Fenjiao banana were acetate, butyrate, methyl acetate, methyl propionate and methyl butyrate, which were different from Brazilian banana. Except for isoamyl acetate, including butanoic acid, 1-methylhexyl ester, hexyl acetate, butanoic acid, 3-methyl-3-methylbutyl ester and propionic acid, 3-methyl-3-methylbutyl ester contents were very high, and they were the main volatile compounds in Fenjiao banana. Some propionate and octanoate esters were generated during the later ripening stage in the Fenjiao fruit, which also contribute to the fragrance of hybrid strawberry [32]. Hexyl acetate is also a characteristic aromatic compound of apple fruit [33]. Therefore, the aroma of Fenjiao banana is similar to that of apple and strawberry. During the later fruit ripening stage, the Fenjiao fruit produced propanoic acid, 2-methylbutyl ester, octanoic acid, 3-methyl butyl ester and 3-methylbutyl decanoate, which form a special kind of aroma. Ethylene plays an important role in the ripening of climacter fruits by regulating an array of ripening-associated processes and the biosynthesis of aromatic compounds [34]. It has been shown that ethylene is important in the production of aromatic volatiles in some climacter fruit, such as banana [35], apple [34], tomato [36] and sweet melon [37]. Otherwise, its inhibitory effect on ethylene biosynthesis in these fruits can reduce the production of aromatic compounds [37]. It was reported that in apple, the metabolism of volatile compounds is ethylene-dependent, and ethylene significantly enhanced volatiles production, whereas 1-MCP (1-methylcyclopropene, a nontoxic antagonist of ethylene) treatment inhibited volatiles [34]. In apple, the expression of most of the genes involved in the biosynthesis of aromatic compounds is regulated in an ethylene-dependent manner. In citrus fruit, which are considered non-climacteric fruit, ethylene affects the production of aromatic compounds in a variety-specific manner [8]. Volatile esters are generated mainly by esterification of alcohols and acyl-CoA derived from both fatty acid and amino acid metabolism [38]. Fatty acids serve as ester precursors and are metabolized through two major pathways: \(\beta\)-oxidation and the lipoxygenase (LOX) system [39]. LOX may play a major role in the formation of straight-chain volatile compounds in fruits [40]. The enzyme LOX catalyzes the hydroperoxidation of polyunsaturated fatty acids.