2 octanol

Chromatographic
standards α-terpineol, geraniol, linalool, β-damascenone,
β-ionone, benzaldehyde, 2-phenylethanol, benzyl alcohol, octanoic
acid, decanoic acid, (E)-2-hexenal, hexanal, 1-hexanol, 2-hexen-1-ol,
2-octanol (internal standard, I.S.), and the reagent NaCl and ethanol
(EtOH) were purchased from Merck (Darmstadt, Germany). Water was purified
through a Milli-Q system Millipore (Bedfords, MA, USA).
Thin
film (TF) with polidimetilsiloxane and carboxen (PDMS/CAR) (carbon
fabric film thickness 450 μm), liners packed with Tenax TA,
and borosilicate magnetic stirrers were obtained from GERSTEL GmbH
& Co (Mülheim an der Ruhr, Deutschland). The BP21 capillary
column (50 m length, 0.25 mm i.d., and 0.25 μm film thickness)
was purchased from SGE (Ringwood, Australia).
Blender was bought
from Philips (Amsterdam, Netherlands). The refractometer,
oven, and six-position stirrer plates were purchased from Actylab
(Logroño, La Rioja, Spain). Gas chromatography–mass
spectrometry (GC–MS) was purchased from Agilent Technologies
(Palo Alto, CA, USA). The autosampler system consisted of a multipurpose
sampler (MPS) equipped with a tube tray, a thermal desorption unit
(TDU), and a cooled injection system (CIS-4) connected to a cryocooling
system. MPS and automated TDU were provided from GERSTEL.

The chemical compounds and standards used in this work were hexane (HPLC grade), ethyl hexanoate (98%), and methanol (HPLC grade) from Merck (Darmstadt, Germany); 2-octanol (99%), undecane (99%), (+) camphene (80%), β-myrcene (90%), D-limonene (97%), linalool (95%), geraniol (98%), geranyl acetate (97%), humulene (96%), (−)-caryophyllene oxide (97%), and n-alkanes C₈–C₂₁ (99%) provided by Sigma Aldrich (Castle Hill, NSW, Australia); and α-pinene (95%), β-pinene (94%), and caryophyllene (90%) from TCI (Tokyo, Japan).
The hop samples Azacca (AZAC) and Loral (LORA) were kindly donated by Carlton & United Breweries (Asahi-CUB, Abbotsford, Australia) and the samples Cascade (CASC), Enigma (ENIG), and Zappa (ZAPP) were obtained from various other local suppliers. All samples were obtained in the format of pellet type 90, stored in the presence of nitrogen, and kept in a freezer until ready for analysis. More information about the hop samples is presented in Table S1 of the Supplementary Materials.

Huangjiu samples in Shaoxing region (S1, S2) fermented by glutinous rice and japonica rice, respectively, were provided by Zhejiang Pagoda Brand Shaoxing Rice Wine Co., Ltd., Shaoxing City, Zhejiang Province, China. The samples were brewed using the same Jianhu water, wheat Qu (a saccharification starter) and Jiuyao (a fermentation starter) with the same ratio. And the same brewing technique including soaking and steaming rice, fermentation (primary fermentation at 28°C for 3–5 days, then secondary fermentation at medium-low temperatures for about 90 days), filtration, pressing, clarification and storage was applied. All of the samples were stored at 4°C and they were analyzed within 1 month after being transferred to the laboratory.
The regents, aspartate, leucine, lysine, proline, histidine, arginine, 2-octanol (internal standard) and n-alkane standards (C₅–C₃₀) of chromatographic grade and purity ≥98.0% were obtained from Sigma Aldrich (Shanghai, China).

The profile of volatile compounds was mainly determined using headspace solid-phase micro-extraction (HS-SPME) [24 (link)] combined with gas chromatography-mass spectrometry (GC-MS) (Agilent 7890-B/5977A MS system, Agilent Technologies, Little Falls, DE, USA). The sample treatment and instrument operating parameters were carried out according to the methods described in our previous study [25 (link)]. The chromatographic peaks were qualitatively determined by matching the NIST 17s mass spectral library and Kovats index, which was calculated by the analysis of the C7–C40 n-alkane standard (Sigma-Aldrich, St. Louis, MO, USA) under the same chromatographic conditions as the samples. The concentration of each volatile compound was calculated quantitatively by the normalized method based on the peak area of the internal standard compound (2-octanol, 10 mg/L) and the correction factor of the reference compounds purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA).

Methyl 2-methylbutanoate, (1R)-(+)-a-pinene, ethyl butanoate, camphene, β-Pinene, isoamyl acetate, 3-carene, myrcene, methyl hexanoate, dipentene,γ-terpinene, (Z)-β-ocimene, isoamyl butanoate, hexylacetate, terpinolene, (Z)-3-hexenyl acetate, 1-hexanol, allyl hexanoate, leaf alcohol, ethyl-caprylate, benzaldehyde, linalool, menthyl acetate, isobornyl acetate, β-caryophyllene, hexyl hexanoate, ethyl caprate, (Z)-3-Hexenyl hexanoate, citronellyl propanoate, nerol, allyl cyclohexylpropionate, geraniol, benzyl butanoate, γ-octanoic lactone, γ-decalactone, neryl acetate, and absolute ethanol were obtained from Shanghai Titan technology Co., Ltd. (Shanghai, China). The 2-octanol, used as internal standards (IS), and a mixture of n-alkane standards (C7-C30) were purchased from Sigma-Aldrich (St. Louis, MO, USA). All of the above chemicals were of GC quality and used without further purification. Ultrapure water was purified from a Milli-Q purification system (Millipore, Bedford, MA, USA).

All the standards and reagents, including 2-octanol, gallic acid, 1,1-diphenyl-2-picrylhydrazyl (DPPH), and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), were purchased from Sigma-Aldrich (St. Louis, MO, USA). All medium, including the plate counting medium, lauryl sulfate peptone broth, bright green lactose bile broth, and Bengal red medium, were purchased from Hope Bio-Technology Co., Ltd. (Qingdao, China).