## 2 Materials and Methods
### Headspace Solid- Phase Micro-Extraction Gas Chromatography-Mass Spectrometry (HS-SPME-GC-MS)  
The HS-SPME-GC-MS method from [PERSON] et al. [9] was used to analyse VOCs. A 2 cm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) (Supelco Inc., Bellefonte, PA, USA), 23 gauge SPME fiber was used for sampling. Samples were incubated at 40 \({}^{\circ}\)C with a conditioned stir bar before exposing the fiber for 30 min at 40 \({}^{\circ}\)C at 600 rpm. The samples were analysed using an Agilent (Mississauga, ON, Canada) 7890A gas chromatograph coupled to a 5975C mass selective detector (MSD) equipped with a Gersal MPS2 XL autosampler (Linthicum Heights, MD, USA). The GC was equipped with a Deans Switch and two columns: a HP-5 MS 5% phenyl methyl siloxane column (30 m, 0.25 mm i.d., 0.25 \(\upmu\)m film thickness) coupled with a secondary DB-Wax capillary column (30 m, 0.25 mm i.d., 0.25 \(\upmu\)m film thickness) (Agilent Technologies Inc., Santa Clara, CA, USA). The liner was a SPME inlet liner (0.7 mm i.d. ; Supelco). Helium was used as the carrier gas with a flow rate of 0.5 mL/min in the first column, and 1.5 mL/min in the second column. Owen temperature programming began at 35 \({}^{\circ}\)C for 3 min, and then increased 3 \({}^{\circ}\)C/min up to 105 \({}^{\circ}\)C where it was held for 10 min. Temperature was then increased by 2 \({}^{\circ}\)C/min up to 140 \({}^{\circ}\)C, before holding for 10 min. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Aroma Compound** & **Aroma Descriptors** & \begin{tabular}{c} **Odor Threshold** \\ **(\%/L)** \\ \end{tabular} & \
\begin{tabular}{c} **Purity** \\ **(\%)** \\ \end{tabular} & **CAS No.** & **Supplier** \\ \hline d11 Ethyl hexanoate ISTD & N/A & N/A & 98.7 & 2159-19-5 &
\begin{tabular}{c} CDN Isotopes, \\ Pointe-Claire, \\ QC, Canada \\ \end{tabular} \\ \hline \multicolumn{5}{c}{_Ethyl ester. Linear fatty acid derivatives_} \\ \hline Ethyl octanoate & Fruity, apricot, pineapple & 580 \({}^{\circ}\) & \(>\)99 & 106-32-1 & Sigma Aldrich \\ Ethyl hexanoate & Apple, blackberry & 62 \({}^{\mathrm{d}}\) & 99 & 123-66-0 & Sigma Aldrich \\ Ethyl butanoate & Acid fruit, candy, strawberry & 20 \({}^{\mathrm{b}}\) and 125 \({}^{\mathrm{d}}\) & 99 & 105-54-4 & Sigma Aldrich \\ \hline \multicolumn{5}{c}{_Ethyl esters: Branched acid derivatives_} \\ \hline Ethyl isobutyrate & Apple, citrus, & 15 \({}^{\mathrm{c}}\) & 99 & 97-62-1 & Sigma Aldrich \\ Ethyl isovalerate & Mint, fruit & 3 \({}^{\mathrm{c}}\) & 98 & 108-64-5 & Sigma Aldrich \\ Ethyl-2-methylbutyrate & Sweet fruit & 18 \({}^{\mathrm{c}}\) & 99 & 7452-79-1 & Sigma Aldrich \\ \hline \multicolumn{5}{c}{_Alcohals_} \\ \hline
2-Phenylethanol & Roses & 14,000 \({}^{\mathrm{c}}\) & 99 & 60-12-8 & Sigma Aldrich \\
1-Hexanol & Herbal, green, grass & 8000 \({}^{\mathrm{b}}\) & 99.5 & 111-27-3 & Sigma Aldrich \\ \hline \end{tabular}  
* [PERSON] [10], odour thresholds determined in wine; \({}^{\mathrm{b}}\) [PERSON] et al. [11], odour thresholds determined in 10\% ethanol/water solution; \({}^{\mathrm{c}}\) [PERSON] et al. [12], odour thresholds determined in 10\% ethanol/water solution with 7 g/L glycerol at pH 32; \({}^{\mathrm{d}}\) [PERSON] et al.[13] odour threshold determined in 10\% ethanol/water solution at pH 3.2.  
\end{table} 
Table 1: List of volatile aroma compounds analysed, their aroma descriptors and odour thresholds. Temperature went through one more ramp up of 4 \({}^{\circ}\)C/min up to 250 \({}^{\circ}\)C, before holding for a final 10 min. The run time for this method was 101 min. The MSD interface was held at 250 \({}^{\circ}\)C. The inlet temperature was 250 \({}^{\circ}\)C and the SPME fiber was desorbed in splitless mode. The solvent delay was 5 min. The fiber was prebaked for 10 min and post baked for 20 min. Samples were warmed at 40 \({}^{\circ}\)C and stirred at 600 rpm for 1 min before being exposed to the fiber for 30 min at 40 \({}^{\circ}\)C with stirring at 600 rpm, followed by desorption in the inlet for 10 min.