2 5 dimethylpyrazine

Green coffee beans (C. arabica Sitio Chapada from Brazil and C. robusta from Vietnam) were purchased from Trini Coffee (Goyang, Korea). DL-Malic acid (≥98%), citric acid (≥98%), L-(+)-tartaric acid (≥99.5%), and succinic acid (≥99%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Green coffee beans and organic acid powder were stored at room temperature.
For the analysis of volatile flavor compounds, C7 − C40 n-alkane standard and a divinylbenzene/Carboxen/Polydimethylsiloxane (50 μm DVB/CAR/PDMS) solid-phase microextraction (SPME) fiber were purchased from Supelco, Inc. (Bellefonte, PA, USA). Hexane, high-performance liquid chromatography (HPLC)-grade water, and HPLC-grade ethyl acetate were purchased from J.T. Baker (Philipsburg, NJ, USA). Sodium chloride (NaCl) was purchased from Samchun (Seoul, Korea). Quinoxaline, 2-methyl pyrazine, 2,5-dimethyl pyrazine, 2,6-dimethyl pyrazine, ethyl pyrazine, 2-ethyl-6-methyl pyrazine, furfural, 2-acetyl furan, furfuryl acetate, 5-methyl furfural, and furfuryl alcohol were purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan).
For the analysis of α-DCs, MGO (purity 40%), DA (purity 97%), o-phenylenediamine, and 1-methylpyrazole were purchased from Sigma-Aldrich. GO (purity 39%) was purchased from Tokyo Chemical Industry Co., Ltd. HPLC-grade water and HPLC-grade ethyl acetate were purchased from J.T. Baker.