Volatile collection, gas chromatography and mass spectrometry

Volatiles were collected from 1 ml of fruit juice or 13 g of noni fruit at different ripening stages in capped 15 ml glass vials with poly-tetra-fluoroethylene-lined silicone septa (Sigma, 23242-U). After penetrating the septum of the cap with a Solid Phase Microextraction (SPME) fibre holder, the SPME fibre (grey hub plain, coated with 50/30 μm divinylbenzene/carboxen on polydimethylsiloxane on a StableFlex fibre (Sigma, 57328-U)) was exposed to the headspace of each vial for 30 min at room temperature. For collection of headspaces in the trap assay, a single noni juice trap was placed in the arena and odours were collected with SMPE for 5 min at 0 h, 5 h and 10 h after placement. For collection of headspaces in the wind tunnel assay, samples were captured with SPME for 10 min at the landing platform and the release platform directly after noni juice application. After each odour collection, the SPME fibre was retracted and immediately inserted into the inset of a Gas Chromatography-mass spectrometry (GC-MS) system (Agilent 7890B fitted with MS 5977A unit) for desorption at 260ºC in split mode (split ratio 100:1). The GC was operated with a HP-INNOWax column (Agilent 19091N-133UI). Samples were injected at an initial oven temperature of 50°C; this temperature was held for 1 min and gradually increased (3°C min^-1) to 150°C before holding for 1 min. Subsequently, the temperature was increased (20°C min^-1) to 260°C and held for 5 min. The MS-transfer-line was held at 260°C, the MS source at 230°C, and the MS quad at 150°C. MS spectra were taken in EI-mode (70 eV) in a 29-350 m/z range. Between different collections, the SPME fibre was conditioned at 270°C for 15 min. All chromatograms were processed using MSD ChemStation F.01.03.2357 software. Volatile compounds were identified using the NIST library and matched to standards of the Max-Planck-Institute for Chemical Ecology library. For quantification, peak areas were measured for 3 replicates for each sample. Note that SPME allows only for a qualitative analysis of odour compositions as well as for an estimate of changing ratios of odours across different samples. Vapour pressure values for hexanoic acid, methyl hexanoate and 2-heptanone were described previously (www.thegoodscentscompany.com)^42,43.