Formic acid

Atrazine was purchased from J&K Scientific (Beijing, China), with its purity ≥ 98.8%. Methanol and formic acid were of HPLC grade and were purchased from J&K Scientific (Beijing, China) and Kermel Chemical Reagent Co., Ltd. (Tianjin, China), respectively. A Milli-Q water purification system (MilliporeSigma, Burlington, MA, USA) was employed. Atrazine was prepared as a stock solution of 20 mg/L. The stock solution was kept in reserve at 4 °C until use.
Main testing instruments: Ultra-high-performance liquid-chromatography electrospray triple-quadrupole mass spectrometer (UPLC–ESI–MS/MS, Waters, Milford, MA, USA); an ACQUITYTM UPLC BEN C8 chromatographic column (2.1 mm × 50 mm, 1.7 μm, Waters, Milford, MA, USA).

An aqueous extract of smokeless tobacco (STE) (purity > 95.5%) was supplied by Shanghai Tobacco Group Co., Ltd. (Shanghai, China). STE powder was stored at 4 °C, protected from light and moisture. A nicotine standard (purity 99.0%, batch No. S18379725) was purchased from Toronto-Research-Chemicals, Inc. (TRC, Toronto, ON, Canada). An internal standard, fennel (purity 99.0%, batch No. ED4XO-ON) was purchased from J & K Chemical Ltd. (Shanghai, China). Mass spectroscopy grade acetonitrile, methanol, and formic acid were also purchased from J & K Chemical Ltd. (Shanghai, China). All other chemicals used were of the highest commercial grade available. The GC-MS analysis of nicotine was conducted at the College of Pharmacy, Second Military Medical University (Shanghai, China). For oral gavage, STE was suspended in distilled water at concentrations of 0.75, 1.50 and 3.00 mg·nicotine/mL and fresh samples were prepared once every three days.

Analytical standards N^ε-carboxymethyl-lysine (CML) and glyoxal (GO) were obtained from J&K Scientific Co., Ltd. (Beijing, China), and Yuan Ye Biotechnology Co., Ltd. (Shanghai, China), respectively. The model of dairy food was prepared by sodium caseinate and d-glucose, which were purchased from West Dragon Science Co., Ltd. (Shantou, Guangdong, China). Standards of p-coumaric, ferulic, caffeic, syringic, sinapic, vanillic, and chlorogenic acids (analytical grade, ≥98%) were purchased from Shanghai Tian Biotechnology Co., Ltd. (Shanghai, China). The organic reagents like acetone, methanol, and acetonitrile were purchased from Sinopharm Chemical Reagent Co., Ltd. (Beijing, China). The other reagents of gallic acid, formic acid, sodium carbonate, disodium hydrogen phosphate dodecahydrate and sodium dihydrogen phosphate dehydrate, sodium borate, sodium hydroxide, and sodium borohydride were purchased from J&K Scientific, Co., Ltd. (Beijing, China). Folin–Ciocalteu reagent (analytical grade), 1,1-diphenyl-2-picrylhydrazyl (DPPH, analytical grade), and O-phenylenediamine was purchased from Source Biological Technology Co., Ltd. (Shanghai, China). DDW was prepared using a WaterPro water purification system (Labconco Corp., Kansas City, MO, U.S.A.). The baijiu vinasses were provided by a large local baijiu manufacturer.

Tartary buckwheat seeds were obtained from Sichuan Jing Cheng Seeds Development Co., Ltd. (Sichuan, China). Reference standards of RU (purity ≥ 99.9%), QU (purity > 98.0%), and KA (purity > 98.0%) were from Shanghai Pharmaceutical Technology Co., Ltd. (Shanghai, China). Ethanol, methanol, formic acid, acetonitrile, and other chemical reagents were supplied from J&K Scientific (Beijing, China). The Escherichia coli (ATCC 25922) and Lactobacillus casei (ATCC 393) were obtained from Biobw Biotechnology Co., Ltd., (Beijing, China). Deionized water was prepared with Hitech-K flow water purification system (Hitech Instruments Co., Ltd., Shanghai, China). 1,1-diphenyl-2-picrylhydrazyl (DPPH) Malondialdehyde (MDA) test kit was purchased from the Nanjing Jiancheng Bioengineering Institute (Nanjing, China).