Butanoic acid

The necessary chemical standards were obtained from the suppliers shown in parenthesis. Acetic acid, 99% (Merck, Darmstadt, Germany); 3-methyl butanal, 98%; butanoic acid, 97%; pentan-2-one, 98%; dihydro-2-methyl-3(2H) furan, 97%; 2-methylpyrazine, 98%; 3-furaldehyde, 99%; 2-furamethanol, 97%; 2-acetyl furan, 99%; 2-ethylpyrazine, 98%; benzaldehyde, 98%; 5-methyl-2-furfural, 99%; 2-pentyl furan, 98%; ethyl furfural, 98%; limonene, 99%; phenyl acetaldehyde, 99%; 2-acetylpyrrole, 98%; 2-pyrrole carboxaldehyde, 97%; 3-methyl phenol, 99%; 2-ethyl-3,5-dimethylpyrazine, 98%; linalool, 98%; 5-hydroxy methyl furfural, 99%; β-cyclocitral, 97%; 2,6-dimethoxyphenol, 98%; β-caryophyllene, 98%; α-ionone, 98%; α-copaene, 99%; β-ionone, 98% (Aldrich, Steinheim, Germany).

Reference odorants were obtained from the
commercial sources given in parentheses: acetic acid (Merck, Darmstadt,
Germany); butanoic acid, δ-decalactone, δ-dodecalactone,
ethyl butanoate, ethyl hexanoate, hexanoic acid, 3-methylbutanal,
3-methylbutanoic acid, 3-methyl-1-butanol, pentanoic acid, 2-phenylacetic
acid, and 2-phenylethanol (Sigma-Aldrich Chemie, Taufkirchen, Germany).
Diethyl ether, sodium carbonate, sodium chloride, and anhydrous
sodium sulfate were purchased from Merck (Germany). Liquid nitrogen
was obtained from Linde (Munich, Germany). Dess-Martin periodinane
and 4-methylumbelliferyl butanoate were obtained from Sigma-Aldrich
Chemie. Diethyl ether was freshly distilled prior to use.

Reference compounds of the odorants identified
were obtained from the commercial sources given in parentheses: acetic
acid (Merck, Darmstadt, Germany); butane-2,3-dione, butanoic acid,
γ-decalactone, δ-decalactone, γ-dodecalactone, δ-dodecalactone,
ethyl butanoate, ethyl hexanoate, 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone, hexanoic acid, 3-hydroxy-4,5-dimethyl-2(5H)-furanone, 4-hydroxy-3-methoxybenzaldehyde (vanillin),
2-isopropyl-3-methoxypyrazine, 3-methylbutanal, 2-methylbutanoic acid,
3-methylbutanoic acid, 3-methylbutanol, 2-methylpropanoic acid, γ-nonalactone,
(E)-2-nonenal, pentanoic acid, 2-phenylacetic acid
and 2-phenylethanol (Sigma-Aldrich Chemie, Taufkirchen, Germany);
and 4-ethyloctanoic acid (ABCR GmbH & Co. KG, Karlsruhe, Germany).
The following reference compounds were synthesized as previously
described: (Z)-2-nonenal^{27 (link)} and trans-4,5-epoxy-(E)-2-decenal.^{28 (link)}

The standards of volatile compounds were purchased from Sigma-Aldrich (St. Louis, MO, USA), including isobutanol, 3-methyl-1-butanol, cis-3-hexen-1-ol, 1-hexanol, heptanol, octanol, phenethyl alcohol, 2,6-nonadien-1-ol, dodecanol, ethyl acetate, isoamyl acetate, ethyl lactate, ethyl hexanoate, ethyl octanoate, diethyl succinate, phenethyl acetate, ethyl decanoate, butanoic acid, hexanoic acid, octanoic acid, dodecanoic acid, octanal, (2e,6z)-2,6-nonadienal, benzaldehyde, furfural, citronellol, linalool, rose oxide, geraniol, nerol, β-damascenone, β-ionone, nerolidol, hexanal, guaiacol, 4-Ethylphenol, and 2-octanol which were used as the internal standard.
Folin–Ciocalteu reagent and sodium chloride were purchased from Beijing Chemical Works (Beijing, China). Potassium hydrogen tartrate were purchased at Kemiou Chemical Reagent Co. (Tianjin, China). Bovine serum albumin was obtained from Asahi Kasei Corporation (Tokyo, Japan). Deionized water (<18 MW resistance) was purified by using a Milli-Q purification system (Molecular, Chongqing, China). Bentonite, soybean protein and potassium metabisulfite were purchased from Lallemand Company (Lallemand, Toulouse, France).

All 23 standard compounds used for the quantification analysis were purchased from Sigma-Aldrich (purity 99.0%, all chromatographic grade), including butanoic acid, acetic acid, thujone, methyl eugenol, p-cymene, α-pinene, diallyl disulphide, α-terpineol, β-caryophyllene, β-myrcene, 1,8-cineole, D-limonene, linalool, methional, nonanal, phenylethanal, ethyl caprylate, 4-methyl-5-thiazoleethanol, (E)-2-octenal, (E)-2-heptenal, humulene, acetophenone, and linalyl acetate. The internal standard (2,4,5-trimethylthiazole) and n-alkanes (C8–C30) used to calculate the retention index (RI) were of chromatographic grade and purchased from Sigma-Aldrich (St, Louis, MO, USA). Diethyl ether and n-pentane for dilution and preparation of sample were obtained from Thermo Fisher Scientific Inc. (Waltham, MA, USA). High purity helium (99.999% purity) and nitrogen (99.99% purity) were purchased and produced by Beijing Tianlirenhe Trading Co., Ltd. (Beijing, China).

Authentic standards were obtained from commercial sources: 3-methylbutanal, hexanal, furfural, heptanal, octanal, phenylacetaldehyde, α-pinene, 5-methyl-2-furancarboxaldehyde, nonanal, decanal, ethanol, 1-propanol, 2-butanol, 3-methyl-1-butanol, propylene glycol, 1-pentanol, 2-furanmethanol, 1-hexanol, phenol, 2-methylphenol, 4-methylphenol (p-cresol), 3-methylphenol, 2-methoxyphenol, 2,6-dimethylphenol, 2-methoxy-3-methylphenol, creosol, 4-ethyl-2-methoxyphenol, 2-methoxy-4-vinylphenol, 2,6-dimethoxyphenol, octane, eugenol, trans-isoeugenol, 1-hydroxy-2-propanone, 2-cyclopentenone, cyclooctane, 2-methyl-2-cyclopentenone, 3,4-dimethyl-2-cyclo-pentenone, benzoic acid, 2-hydroxy-3-methyl-2-cyclopentenone, 3-methyl-2-cyclopentenone, acetic acid, 2,3-dimethyl-2-cyclopentenone, 3-ethyl-2-cyclopentenone, butanoic acid, styrene, 3-ethyl-2-hydroxy-2-cyclopentenone, 2,3,4-trimethylpentane, 2-furylmethylketone 2,3,3-trimethylpentane, 2,2,8-trimethyldecane, propanoic acid, 3-methyl-3-heptene, (Z)-2-octene, d-limonene, and ethyl hexanoate were purchased from Sigma-Aldrich (Shanghai, China). 2-Octanol (internal standard) and n-alkane standards (C₆–C₃₀) were purchased from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA). All substances are AR, at least 97% purity. The purification system from Milli-Q (Millipore, Bedford, MA, USA) to obtain purified water.

All the chemicals ethyl acetate (EA; CAS#141-78-6), pentane-2,3-dione (CAS#600-14-6), hexane-2,3-dione (CAS#3848-24-6), hexane-3,4-dione (CAS#4437-51-8), 3-oxobutan-2-yl acetate (2-acetoxybutan-3-one, CAS# 4906-24-5), butanoic acid (CAS#107-92-6), bis (4-nitrophenyl) phosphoric acid (BNPP; CAS#645-15-8) and diethyl ether (CAS#60-29-7) were purchased from Sigma Aldrich (Sigma Aldrich, St Quentin Fallavier, France).