Trimethylpyrazine

Pyridine, 2,4,6-, 2,3,5-trimethylpyridine, 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, 3,5-dimethylpyridine, 2,3,5-trimethylpyrazine, 2,3-, 2,5-, 2,6-dimetylpyrazine, 2,3-diethyl-5-methylpyrazine, 3-methylpyridazine, pyrazine, 2,3,5,6-tetramethylpyrazine, 2-pyrazinecarboxylic acid, pyrazine-2,3-dicarboxylic acid, 5H-5-methyl-6,7-dihydrocyclopenta[b]pyrazine, and 5,6,7,8-tetrahydroquinoxaline were purchased from either Sigma-Aldrich (Darmstadt, Germany) or Fluka (Berlin, Germany), and were of the highest purity available. The chemicals were used without additional purification. Nutrient agar, nutrient broth, and yeast extract were purchased from Oxoid (Hampshire, UK). The agar was from Merck (Darmstadt, Germany). The inorganic compounds were purchased from Lachema (Brno, Czech Republic). All compounds for DNA manipulation were purchased from Thermo Fisher Scientific (Vilnius, Lithuania).

2-Methyl-1-propanol, 3-methyl-1-butanol, 3-methyl-butanal, 3-octanone, p-xylene, styrene, benzeneacetaldehyde, phenylethyl alcohol, 4-ethyl-phenol, 2,5-dimethyl-pyrazine, trimethyl-pyrazine, and 3-ethyl-2,5-dimethyl-pyrazine were purchased from Sigma-Aldrich China Inc. (Beijing, China). The 18 amino acid standards, including glycine (Gly), asparagine (Asn), alanine (Ala), glutamic acid (Glu), lysine (Lys), arginine (Arg), proline (Pro), valine (Val), tyrosine (Tyr), isoleucine (Ile), leucine (Leu), tryptophan (Try), serine (Ser), histidine (His), threonine (Thr), methionine (Met), cysteine (Cys) and phenylalanine (Phe), were all purchased from Biosharp.
High-performance liquid chromatography (HPLC)-grade acetonitrile was supplied by Tedia Company (Fairfield, OH, USA). Phenylisothiocyanate (PITC, lot code: 10113227) was purchased from Alfa Aesar Chemical Co. Ltd (Tianjin, China), with a purity higher than 97%. Triethanolamine (TEA, analytical grade) and n-hexane (analytical grade) were purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Pure water was obtained using a Milli-Q purification system (Millipore, Bedford, MA, USA).

Soybeans, raw wheat flour and edible salt (NaCl) were purchased from a local supermarket (Zhenjiang, China, 2021). 3-Methylbutanal, ethanol, 3-methyl-1-butanol, ethyl propanoate, ethyl acetate, ethyl isovalerate, 2-phenylethanol, benzeneacetaldehyde, 3-(methylthio) propyl acetate, ethyl 3-(methylthio) propionate, methyl benzoate, (E)-β-damascenone, 2-phenylethyl acetate, 2-furanmethanol, 3-methylthio-1-propanol, 3-methylthio propanal, 2,6-dimethyl pyrazine, trimethyl pyrazine, 2-acetyl pyrroline, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) and 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF) were all ordered from Sigma-Aldrich (Shanghai, China, 2021). 3-Furaldehyde, 4-ethylphenol, 4-ethylguaiacol, 4-vinylguaiacol, 3-methylbutanoic acid, acetic acid, 2-methylbutanoic acid, dimethyl trisulfide, 1-octen-3-ol and C6-C33 n-alkanes were provided by Aladdin Holdings Group (Shanghai, China, 2021). Other analytically pure reagents were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China, 2021). A. oryzae 3.042 were obtained from the Guangdong Institute of Microbiology (Guangzhou, China, 2021).