2 pentanol

Gas mix 1 : 3 ¹⁸O₂ oxygen (98%) and ¹⁴N₂ nitrogen was from CK Gas Products Ltd. (Hook, UK). hexanoic acid-2, 2-D₂ acid (98 atom % D); hexanoic-D₁₁ acid (98 atom % D); hexanoyl-CoA trilithium salt hydrate (C6:0); hexanoylcarnitine, hexanoic acid, octanoic acid, 4-methyl-2-pentanone (MIBK) >99%, cyclohexanone 99.8%, 2-pentanone 99.5%, 2-pentanol 98%, ethyl 3-oxohexanoate (ethyl butyrate) 98% purities, and pentane were from Sigma-Aldrich (Gillingham, UK). Hexane (HPLC grade) was from Fisher Scientific UK Ltd. (Loughborough, UK). Blue cheese and margarine were obtained commercially. In preliminary studies (Section 3.2), 250 μL of a 1 in 2,000 dilution of cyclohexanone in water was added as internal standard (IS). In later experiments (Sections 3.3 and 3.4), the IS was 20 μL of a 1 in 1,000 dilution of MIBK in water. Working solutions of hexanoic acid (¹H or deuterated) were prepared as dilutions in melted margarine (1 μL/mL; 8 mmol/L).
Carboxen-polydimethylsiloxane 75 μm film thickness solid-phase microextraction (SPME) fibres and SPME fibre syringe holders were from Supelco (Poole, UK); headspace (HS) vials (22 mL) with soft silicone rubber seals (20 mm diameter) and aluminium caps were from Alltech Associates Ltd. (Carnforth, UK). Water was deionised by reverse osmosis.

Peptone, D-( +)-glucose, yeast extract, YPD media, 2-pentanol, citric acid monohydrate, tri-sodium citrate di-hydrate, 99% hexane, and 98% d-Limonene were obtained from Sigma-Aldrich, South Africa. The enzyme cocktail, Viscozyme^® was obtained from Novozyme. The yeast (S. cerevisiae) was obtained from Anchor Yeast, South Africa.
The equipment used for ultrasound generation is a 24 kHz UP200St ultrasound system. It has a maximum power output of 200W with a maximum amplitude of 190 µm. This is produced by a horn tip transducer of surface area equivalent to 0.38 cm² and a 12 ml flow cell, manufactured by Hielscher, Germany. The bioreactor system used is a product of Glaschem, South Africa. It consisted of a control system, a 1L glass reactor equipped with temperature and pH probes, a stirrer, and a heating jacket connected to a temperature-controlled water bath. Analytical equipment used was the microplate reader ELx800 (Bio Tek Instruments) and UV–Vis spectrophotometer in the Department of Chemical Engineering, Stellenbosch University. Other pieces of equipment used were a heating block, a hot plate, and a halogen lamp-type moisture analyzer manufactured by KERN DERBS.

Sulfuric acid for HPLC analysis was employed (30,743 Honeywell Fluka 95–97%). MEthanol for RP-HPLC was purchased from Merck (34,860, ≥99.9%).
Standard solutions for HPLC (TraceCERT^®, 1,000 mg/L in water) were purchased from Sigma-Aldrich (Milan, Italy). Analyte stock solutions were prepared by dissolving a weighed amount of the pure compound in deionized water and stored at 4°C up to 1 month. Ethanol, ¹³C-labeled Ethanol, acetoin, acetone, butanal, 2-methylbutanal, 3-methylbutanal, butanedione, butanol, 2-methyl-butanol, 3-methyl-butanol, butanone, hexanal, mEthanol, methylacetate, 2-pentanol, propanal, 2-methylpropanal, propanol, 2-methyl-propanol, and sec-butanol were purchased from Sigma-Aldrich (Italy). All chemicals, having purity higher than 99%, were used without any further purification.
Solid-phase microextraction fiber based on 85 um carboxen/polydimethylsiloxane (CAR/PDMS) was employed for the preconcentration of volatile compounds in the HS.
Helium 5.6 IP was purchased from SOL Group Spa (Italy) and was further purified with a super clean filter purchased from Agilent Technologies (United States) to remove water, oxygen, and hydrocarbon contaminants.
Preparation/dilution of samples and solutions was performed gravimetrically using ultrapure water (Milli-Q; 18.2 MΩ cm⁻¹ at 25°C, Millipore, Bedford, MA, United States).