Volatile standards

Volatile standards were purchased from Sigma-Aldrich (St. Louis, MO, USA) and their purity is listed in Table S1. Tartaric acid, dichloromethane (HPLC grade), ethanol (HPLC grade), sodium hydroxide (NaOH), sodium chloride (NaCl), ammonium sulfate ((NH₄)₂SO₄), and sodium sulfate (Na₂SO₄) were purchased from Beijing Chemical Works (Beijing, China). Distilled water was purified from a Milli-Q purification system (Millipore, Bedford, MA, USA).

Four commercial yeast strains, ES488, CY3079, BV818 and VIC, were chosen because of their steady fermentation characteristics and excellent flavor enhancement according to the manufacturer instructions. The strains ES488 and CY3079 (Saccharomyces cerevisiae) were purchased from Enartis (Tracete, Italy) and Lallemand (Montréal, QC, Canada), respectively. Strains BV818 and VIC (Saccharomyces bayanus) were provided from Angel Yeast Co., Ltd. (Hubei, China). Pectinase and potassium metabisulfite were purchased from Enartis (Tracete, Italy). Water was purified through a Milli-Q purification system (Millipore, Bedford, MA, USA). Folin-Ciocalteu reagent was purchased from Beijing Sulaibao Tech Co., Ltd. (Beijing, China). Sodium hydroxide, sodium chloride, ammonium sulfate, aluminum nitrate, sodium sulfate, sodium carbonate, tartaric acid and ethanol were of analytical grade and purchased from Beijing Chemical Works (Beijing, China). The volatile standards used in this study were purchased from Sigma-Aldrich (St. Louis, MO, USA). These standards had a purity above 95%. The internal standard (4-methyl-2-pentanol) was obtained from Sigma-Aldrich (St. Louis, MO, USA) with a 98% purity.

HPLC grade methanol, HPLC grade hexane, and reagent grade ethanol were purchased from Fisher Scientific (Fairlawn, NJ, USA). γ-tocopherol, δ-tocopherol, α-tocopherol, α-tocopherol acetate, and refined olive oil were purchased from Sigma-Aldrich (St. Louis, MO, USA). Volatile standards were purchased from Sigma-Aldrich (St. Louis, MO). The water was obtained from a Milli-Q-Plus water purification system (Millipore, Milford, MA, USA).