2.3.1. Feeding of Alcohols and 2-Keto-4-Methylpentanoic Acid

The feeding experiments were conducted by incubating 10 g of banana pulp slices with different exogenous substrates: 50 μmol of C3–C6 straight chain or branched alcohols, or 2-keto-4-methylpentanoic acid, in a 150-mL conical flask for 90 min at 35 ◦C. The substrates were spotted onto a 40 × 5 mm filter paper strip prior to incubation to enhance evaporation (Figure 2a). After incubation, 1 mL of headspace gas was taken with a glass syringe, and analyzed by gas chromatography (GC, Shimadzu GC-15A, Kyoto, Japan) to target alcohols, aldehydes, or esters. A flame ionization detector was equipped with a packed glass column (2 m × 3 mm) with 20% of tween 20 or 5% of polyethylene glycol 6000. Injector and detector temperatures were 190 ◦C, and oven temperature was 60–120 ◦C, depending on the molecular weight of the target esters. Flow rate of carrier nitrogen gas was 20 mL min−<sup>1</sup> and flaming hydrogen gas was 30 mL min<sup>−</sup>1.
