Tartaric acid

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.

α-Glucosidase from Saccharomyces cerevisiae (G0660-750UN) and phosphate buffered saline (PBS) tablets were purchased from Sigma-Aldrich Co. (St. Louis, US). p-Nitrophenyl-α-_D-glucopyranoside (pNPG) and four organic acids, including caffeic acid, tartaric acid, caftaric acid and chicoric acid were obtained from Yuanye Biotech. Co. (Shanghai, China). Other chemicals in this study were of analytical grade.

Twenty types of Guangdong Hakka Huangjiu were obtained from the local market (Yonghui supermarket, Guangzhou, China). Organic acids including oxalic acid, malic acid, acetic acid, lactic acid, tartaric acid, succinic acid, pyruvic acid, and citric acid were purchased from Yuanye Biotechnology Co., Ltd. (Shanghai, China). Standards of seventeen amino acids were purchased from the Sigma-Aldrich company (Shanghai, China). Fructose, glucose, sucrose, maltose, and lactose were purchased from the Chemical Reagent Factory (Guangzhou, China).

Xanthine, Xanthine Oxidase, and Standards (rutin, malic acid, citric acid, tartaric acid, succinic acid, lactic acid, oxalate, fumarate, glucose, fructose, and sucrose) were purchased from Yuanye (Yuanye Bio-Tech, Shanghai, China). Single Element Standard Solution Fe (1,000 μg/ml) and K (100 μg/ml) were purchased from the National Center (Guobiao, Beijing, China). The acetonitrile and methanol for the high-performance liquid chromatography (HPLC) were from Merck (Merck KGaA, Darmstadt, Germany). The 2,2′-azinobis(3-ethylbenzothiaziline-6-sulfonate (ABTS) was obtained from Solabio (Solabio Sci&Tech, Beijing, China).

Standards for high-performance liquid chromatography (HPLC) were purchased from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China) and included glucose, fructose, sucrose, tartaric acid, malic acid, citric acid, and quinic acid. The HPLC-grade reagents methanol and acetonitrile were acquired from Sigma-Aldrich Chemical Co., Ltd. in Shanghai, China. All additional chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd. in Shanghai, China, and were of analytical quality.