Succinic acid

Analytical purity: sulfuric acid, sodium chloride, potassium chloride, sodium bicarbonate (Beijing Chemical Factory, Beijing, China); tannic acid (Tianjin Guangfu Fine Chemical Research Institute, Tianjin, China); Folin-Denis reagent (US sigma, St. Louis, MO, USA); anhydrous sodium carbonate (Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd., Tianjin, China); glacial acetic acid, hydrochloric acid, anhydrous ethanol, sodium hydroxide, phosphoric acid (Beijing Chemical Factory); potassium hydrogen phthalate, anthrone (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China); anhydrous sodium acetate (Shanghai Hutian Chemical Co., Ltd., Shanghai, China); glucose (Guangzhou Jinhuada Chemical Reagent Co., Ltd., Guangzhou, China).
Chromatographic purity: methanol (TEDIA Reagents, Fairfield, OH, USA); succinic acid, fumaric acid, malic acid, citric acid anhydrous (Shanghai Yuanye Biotechnology Co., Ltd., Shanghai, China); 4-methyl-2-pentanol (Shanghai Lianshuo Biotechnology Co., Ltd., Shanghai, China); glacial acetic acid, tartaric acid, lactic acid (Tianjin Fine Chemical Research Institute, Tianjin, China)
Fermentation auxiliaries: CEC01 active dry yeast (Angel Yeast Co., Ltd., Hubei, China); potassium metabisulphite (Yantai Dibs Homebrewer Co., Ltd., Yantai, China).

Red raspberries of the cultivar “Autumn Bless”, one abundant raspberry species in Northeast China, were obtained from a local farm (Harbin, China) in August 2020. The fruits with similar maturity were hand-picked from different trees and then snap-frozen. Frozen red raspberries (40 kg) were mixed, transported to the laboratory in ice box and stored at −80 °C until use. All the standards for high performance liquid chromatography (HPLC) analysis, including rutin, quercetin, chlorogenic acid, ellagic acid, raspberry ketone, epicatechin, catechinic acid, syringic acid, gallic acid, caffeic acid, luteolin, citric acid, L-malic acid, succinic acid, α-ketoglutarate, and so on (HPLC grade), were obtained from Shanghai YuanYe Biotechnology (Shanghai, China).

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.

Controls, consisting of sugars (fructose, sorbitol, glucose, sucrose), organic acids (quinic acid, malic acid, citric acid, succinic acid), phenolic compounds (coumaric acid, procyanidin B1, neochlorogenic acid, catechin, vanillic acid, chlorogenic acid, epicatechin, rutin, and quercetin), and 3-octanol were bought from Shanghaiyuanye Bio-Technology Co., Ltd. (Shanghai, China). The reagents for 2,2’-azinobis (3-ethylbenzothiazoline-6-sulphonate) (ABTS⁺), 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and cupric reducing antioxidant capacity (CUPRAC) were bought from TANEE CHEMICAL LTD. Analytical-grade reagents were bought from business sources for the remaining materials.

The standard products with the concentration of 99%, including sugars (sucrose, sorbitol, fructose, glucose), organic acids (quinic acid, malic acid, citric acid, succinic acid), phenolic compounds (p-coumaric, procyanidins b, neochlorogenic acid, catechinic, vanillic acid, chlorogenic acid, epicatechin, rutin, quercetin, kaempferol) and 3-octanol were obtained from Yuanye Biotechnology Co., LTD (Shanghai, China). The 2,2′-azinobis (3-ethylbenzothiazoline-6-sulphonate) (ABTS⁺), ferric reducing antioxidant power (FRAP), 2,2-diphenyl-1-picrylhydrazyl (DPPH), and cupric reducing antioxidant capacity (CUPRAC) reagents were purchased from Beifang Tianyi Chemical Reagents Factory (Tianjin, China). All other chemicals were of analytical grade.