Ascorbic acid

A. auricula polysaccharides were purchased from Shanxi Ciyuan Biotech Co., Ltd. (Shaanxi, China). Potassium bromide (SP, 99%), DPPH (SP, 98%), ABTS diammonium salt (SP, 98%), oxalic acid (98%), sodium hydroxide, ascorbic acid (VC) (analytical standard product, HPLC ≥ 99%) were purchased from Yuanye Biotechnology Co., Ltd. (Shanghai, China). N-butanol, ethyl alcohol, potassium persulfate and other analytic-grade reagents were obtained from the Kelong Chemical Reagent Factory (Chengdu, China).

Fresh Yu Muer fruiting bodies were collected from the Fungus and Vegetable Base, Jilin Agricultural University (Changchun City, Jilin Province, China). Test kits for determining PPO, amino acid (AA) content, plant total phenolics, protein content (BCA assay), and total sugar content were purchased from Suzhou Keming Biotechnology Co., Ltd. Sodium erythorbate and L‐cysteine were purchased from Beijing Solarbio Science and Technology Co., Ltd. Ascorbic acid was purchased from Shanghai Yuanye Biotechnology Co., Ltd. Citric acid was purchased from Tianjin Fuchen Chemical Reagent Factory.

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).

The following chemicals and reagents were purchased from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China): Folin–Ciocalteu reagent, 2,2-diphenyl-1-picrylhydrazyl (DPPH), aluminum nitrate, 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), sodium carbonate, sodium nitrite, aluminum chloride, sodium hydroxide, ascorbic acid, gallic acid, rutin, and Trolox. Analytical grade ethanol was purchased from Sichuan Xilong Science Co., Ltd. (Chengdu, China). Pure water was prepared using a secondary reverse osmosis system (JYS-500L; Shanghai Juyuan Automation Technology Co., Ltd., Shanghai, China).

Fresh hawthorn (variety: Dajinxing) was procured in Nanma Village, Xiaodian District (Taiyuan, China) in early October 2022, with a moisture content of 79%. Citric acid, sodium hydroxide, salicylic acid, ferric chloride, and trichloroacetic acid were purchased from Damao Chemical Reagent Co., Ltd. (Tianjin, China). n-Butanol was obtained from Zhiyuan Chemical Reagent Co., Ltd. (Tianjin, China). Anhydrous ethanol was acquired from Yongda Chemical Reagent Co., Ltd. (Tianjin, China). Sodium tetraborate was sourced from Beijing Solaibao Biotechnology Co., Ltd. (Beijing, China). Chloroform and sulfuric acid were provided by the laboratory. Potassium ferrocyanide was procured from Tianjin Fengchuan Chemical Reagent Technology Co., Ltd. (Tianjin, China). Coomassie Brilliant Blue G250, bovine serum albumin, anthrone, gallic acid and ascorbic acid were purchased from Shanghai yuanye Bio-Technology Co., Ltd. (Shanghai, China). Except for gallic acid, which was used as a standard, all other chemical reagents were of analytical grade.

The high purity (≥97%) standards, including ascorbic acid, vanillic acid, syringic acid, epicatechin, daidzin, glycitin, ferulic acid, genistin, daidzein, glycitein, quercetin, and genistein were purchased from Yuanye Bio-Technology Co., Ltd. (Shanghai, China). Other reagents of analytical grade. Soybeans (Liaodou, yellow seed coat, mainly planted in northern China, weigh 21.6 g of one hundred seeds) were obtained from a local market. R. oligosporus RT-3 isolated, screened and identified from Tempeh in our laboratory was used for soybean fermentation (11 (link), 12 ). The strain was cultivated on potato dextrose agar at 30°C for 3 days. Then, spores produced were scraped in water (1 × 10⁷ spores/mL).