Lactic acid

De Man Rogosa and Sharpe broth/agar (MRS), plate count agar, rose Bengal agar, and yeast extract were purchased from Guangdong Huankai Microbiology Technology Co., Ltd. (Guangzhou, China). Polypeptone, glucose fructose, sucrose, acetic acid, citric acid, lactic acid, malic acid, oxalic acid, and L-ascorbic acid were purchased from Shanghai Yuanye Biotechnology Co., Ltd. (Shanghai, China). 1-Kestose, nystose and 1F-fructofuranosylnystose were obtained from Wako Pure Chemical Industries, Ltd. (Tokyo, Japan). Mass spectrometry (MS)-grade acetonitrile, cyclohexanone, and methanol were obtained from Merck (Darmstadt, Germany). Pure water was obtained using a Milli-Q system (Bedford, MA, USA). Phenol and acetocaustin were obtained from Aladdin Reagent Co., Ltd. (Shanghai, China). Other reagents were of analytical grade and were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

The organic acid standards (L-tartaric acid, lactic acid, malic acid, acetic acid, etc.), as well as polyphenol standards (protocatechuic acid, p-hydroxybenzonic acid, chlorogenic acid, vanillic acid, (-)-epigallocatechin gallate, epicatechin, vanillin, p-coumaric acid, (-)-epicatechin gallate, isoferulic acid, etc.), were purchased from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). Water was purified using a Milli-Q system from Millipore (Bedford, MA, USA).
Isoamyl ethanoate, benzylcarbinyl acetate, isobutyl acetate, butyl acetate, propyl acetate, hexyl acetate β-damascenone, naphthalene, cinnamene, linalool, citronellol, d-limonene, α-terpineol, nerol oxide, ethyl dodecylate, ethyl heptoate, ethyl caproate, ethyl butanoate, ethyl caprylate, ethyl propanoate, ethyl isobutyrate, ethyl n-valerate, etc., were provided by Sigma-Aldrich (Shanghai, China). The internal standard of 4-methyl-1-pentanol was obtained from Tokyo Chemical Industry Co. Ltd. (Tokyo, Japan). The calculation of retention indices (RIs) was used with n-alkanes (C8-C40) purchased from Supelco (Bellefonte, PA, USA).

3-Nonanone (98%, Heowns, Tianjin, China), organic acid standards (oxalic acid, tartaric acid, malic acid, lactic acid, acetic acid, citric acid and succinic acid) were from Shanghai yuanye Bio-Technology Co., Ltd. Catechin standards (C, catechin; EC, epicatechin; GC, gallocatechin; CG, catechin gallate; EGC, epigallocatechin; CAF, caffeine; ECG, epicatechin gallate; EGCG, epigallocatechin gallate.) were from Sigma-Aldrich (Shanghai, China). Saccharomyces cerevisiae (lager yeast, s-33) was from Fermentis (Marquette-lez-Lille, France). 2,2-Diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis (3-ethylbenthiazoline-6-sulfonic acid (ABTS), and tripyridyl triazine (TPTZ) were from Sigma-Aldrich (Shanghai, China). All other chemicals and solvents used were of analytical grade, from local suppliers.

HPLC (Agilent, USA) was used to detect soluble sugars and organic acid components based on the modified method of Liu et al. [26 (link)] The Agilent Zorbax Carbohydrate column was used to separate the sugar component, and the flow rate of the mobile phase (75% acetonitrile: 25% water, v/v) was set as 1 mL/min, the coupled detector was the G1362A refractive index detector (RID, Agilent, USA), and the analysis conditions were the following: column temperature 35 °C; injection volume 10 μL. The Agilent SB-AQ column was used to separate the organic acid components, and the mobile phase (5% methanol: 95% 10 mM KH₂PO₄ solution, v/v, pH = 2.6) flow rate was set to 0.8 mL/min, the coupled detector was the G1314B variable wavelength ultraviolet detector (VWD, Agilent, USA), and the analysis conditions were the following: column temperature 25 °C; injection volume 10 μL. Standards of glucose, fructose, sucrose, malic acid, tartaric acid, shikimic acid, lactic acid, succinic acid, citric acid, and acetic acid (ShanghaiyuanyeBio-Technology Co., Ltd., Shanghai, China) were used for qualitative and quantitative analysis of the samples.

Analytical purity: anthrone (Sinopharm Chemical Reagent Co., Ltd. Shanghai, China); ethyl acetate, concentrated sulfuric acid, phosphoric acid (Beijing Chemical Factory, Beijing, China).
Chromatographic purity: methanol (TEDIA reagent, Fairfield, OH, USA); oxalic acid, quinic acid, malic acid, shikimic acid, lactic acid, citric acid, ascorbic acid (Shanghai Yuanye Biotechnology Co., Ltd. Shanghai, China); 4-methyl-2-pentanol (Shanghai Lianshuo Biotechnology Co., Ltd. Shanghai, China).