## 3 Discussion
The content of total soluble sugar in Fenjiao banana at each period was higher than that of Brazilian banana fruit, indicating that Fenjiao banana fruit are much sweeter than Brazilian banana fruit. Flavor results from the complex interaction of taste (sweetness, sourness) and aroma. Taste is basically determined by sugars and acids [27]. Sugar and acid levels are the main factors affecting fruit flavor acceptability, and high sugar content indicate the sweetness [27]. The most important taste components in banana affecting sweetness are glucose, fructose, and sucrose [12]. Sugar accumulation (along with acids) may also determine aroma intensity [28]. In tomato, it was found that cultivars with the increasing in sugar level enhanced the aroma intensity and made the overall flavor more acceptable. Indeed, sugars are positively correlated with overall flavor acceptability [28]. Ethylene also play an important role in the sugar metabolism. A recent work showed that ethylene affects sugar metabolism in climacter and non-climacter plums [29]. Ethylene reduced sucrose catabolism and induced sucrose biosynthesis in different plum types. In the present work, high ethylene production in Fenjiao fruit than Brazilian fruit was observed, corresponding to high sugars content detected in Fenjiao fruit than Brazilian fruit. Production of aromatic volatile compounds is important to the flavor of banana fruit and is the defining characteristics of different cultivars. The characteristic banana aroma is not derived from just one or a few volatile compounds but is the result of a complex mixture of volatile compounds [30]. Generally, esters provide fruity notes and are responsible for the characteristic aroma of fresh banana fruit. Esters constitute the major class of compounds present in the volatile profile of banana fruit, such as butyl acetate, isoamyl acetate, ethyl acetate, butyl butanoate and isoamyl isobutanoate [21; 31]. The volatile compounds of many banana cultivars have been widely studied, but this is the first report on the aromatic profiles of preferable banana cultivars Fenjiao and Brazilian [21]. Headspace SPME coupled with GC-MS provides a simple, rapid and reliable technique to analyze volatile compounds in banana fruit. In the present work, the volatile compounds of Fenjiao banana fruit and Brazilian banana fruit were determined during different ripening stages. Our results show that 62 and 59 volatile compounds, including esters, alcohols, aldehydes, ketones, hydrocarbons and acids, were detected in the two banana cultivars, respectively. The most abundant aromatic compounds in the two banana cultivars during ripening were isoamyl acetate, butanoic acid, 3-methyl-3-methylbutyl ester, hexanal, _trans_-2-hexanal and 1-hexanol. Differences in the volatiles composition of the two banana varieties and significant variations within the same banana variety were observed at different stages of ripening (Supplementary Figures S1 and S2). However, nine compounds, including acetate, caproate, butyrate, valerate, methyl acetate, methyl propionate, methyl butyrate, C\({}_{6}\)-aldehydes and C\({}_{6}\)-alcohols were shared. In general, as the fruits ripened, the concentrations of unsaturated aldehydes and alcohols decreased, while the concentrations of esters increased significantly. It has been proposed that esters are the main aromatic compounds in banana fruit (_[PERSON]_ AAA group) [15]. [PERSON] et al. determined that acetate, butyrate and 3-methyl butyrate are the most abundant esters in fully ripened banana fruit. Isoamyl acetate represented the characteristic compound of banana fruit. However, other reports found that butyrate and propionate are the main esters in banana fruit (_Musa_ AAA group) [12], and the levels of 2-hexanal, hexyl acetate, butanoic acid, 3-methyl-3-methylbutyl ester, butanoic acid, 3-methylbutyl ester are very high [12; 18].