*3.1. Feeding Alcohols to Banana Pulps to Produce Esters*

When butanol vapor was fed to banana pulp slices (at the "yellow with green tips" stage), butyl ethanoate as well as butyl butanoate were accumulated (Figure 3a). Under anaerobic conditions, those esters were barely accumulated (Figure 3a). Green banana (immediately after ripening was triggered by ethylene) pulp was not able to biosynthesize such esters, but obtained the capacity within one day (Figure 3b). Butyl butanoate production increased continually until the "yellow with green tips" stage (day 3 after ethylene treatment), then gradually declined toward senescence (Figure 3b). Similarly, feeding butanol to fruit pulp of ripe muskmelon, pineapple, pawpaw, strawberry, European pear, and apple, also produced butyl butanoate (data not shown). Figure 3a,b results were confirmed when incubating a banana finger in a 1 L jar with butanol vapor, with a much lower yield (about 20%) of butyl butanoate in comparison to that of pulp slices (data not shown). When feeding other C3–C6 branched or straight chain alcohols to banana pulp instead of butanol, propyl propionate and pentyl pentanoate were produced in comparable amounts to butyl butanoate, but productions of hexyl hexanoate, 3-methylbutyl 3-methylbutanoate, and 2-methylpropyl 2-methylpropanoate were much lower (Figure 3c).

**Figure 3.** Alcohol feeding experiments and production of corresponding esters in banana pulps. Exogenous alcohol (50 μmol) on filter paper was fed into 10 g of banana pulp tissues. (**a**) Effect of anaerobic conditions and butanol feeding to pulps at the "yellow with green tips" stage; (**b**) effect of ripening stage; (**c**) substrate specificity of C3–C6 branched and straight chain alcohols at the "yellow with green tips" stage. Vertical/horizontal line at each marker/column shows average ± SD (n = 3).
