Focus gc

The concentrations of ethanol, acetic acid, and acetoin were quantified in the aqueous extracts in triplicate by gas chromatography with flame ionization detection (GC-FID), using a Focus GC (Interscience, Breda, Netherlands) equipped with a Stabilwax-DA column (Restek, Bellefonte, PA, United States) and a FID-80 detector (Interscience), as described previously (De Bruyn et al., 2017 ). Quantification was performed by external calibration, including 1-butanol as IS [solution of 638 mL of acetonitrile (Thermo Fisher Scientific), 250 mL of ultrapure water (MilliQ; Merck), 12 mL of formic acid (Merck), and 250 μL of 1-butanol (Merck)].

The total fatty acid content was measured according to a modified version of the method described by Kang and Wang (2005). To 30 mg of freeze dried cells in a capped test tube with screw cap (VWR art. no. SCERE5100160011G1 and SCERKSSR15415BY100) 1 ml BF₃/methanol reagent (Merck art. no. 8.01663.0500) and 1 ml heptane (Acros organics art. no. 120340025) was added. After overnight incubation at 70 °C 2 ml water was added and mixed. Subsequently, the tubes were centrifuged at 2000 g for 5 min, and the upper (heptane) layer was transferred to a GC vial and analysed on methylated fatty acids by using a Focus-GC (Interscience) equipped with FID. GC was equipped with a Stabilwax Column (Restek art. no. 10624) and uses hydrogen as carrier gas. The sum of the methylated fatty acids was quantified using methylheptadocanic acid as a standard.