Syringic acid

Foxtail millet husk (dry) was acquired from Jinsu Agricultural Technology Corporation (Henan Province, China). The sample was smashed (RS-FS1401 mill, Royalstar Co., Ltd., Hefei, China) sieved (40-mesh), and then stored at −20 °C.
Betaine and L-lactic acid were obtained from Shanghai Macklin Biochemical Co., Ltd., (Shanghai, China). Acetylcholinesterase, α-glucosidase (from Saccharomyces cerevisiae), and standards (vanillic acid, p-hydroxybenzoic acid, p-hydroxybenzaldehyde, caffeic acid, p-coumaric acid, ferulic acid, syringic acid, rutin, and kaempferol, the purity above 98%) were sourced from Shanghai Yuanye Biotechnology Co., Ltd., (Shanghai, China), while ABTS(2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonate)), DPPH(2,2′-diphenyl-1-picrylhydrazyl), Folin–Ciocâlteu reagent, Trolox (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid), and TPTZ(2,4,6-tris(2-pyridyl)-s-triazine) were acquired from Sigma-Aldrich Chemical Co. (St. Louis, MO, USA). Chromatographic methanol and formic acid were purchased from Thermo Fisher Scientific Reagent Co., Ltd., (Waltham, MA, USA). All other reagents, including glycerol, sodium carbonate (Na₂CO₃), sodium acetate, sodium hydroxide (NaOH), sodium nitrite (NaNO₂), glycol, aluminum trichloride (AlCl₃), ferric chloride (FeCl₃), and methanol, were purchased from Tianjin Deen Chemical Reagent Co., Ltd. (Tianjing, China).

Acetonitrile (HPLC-grade) was purchased from Adamas reagent, Ltd. (Shanghai, China). All the polyphenol standards (gallic acid, proanthocyanidin B2, epicatechin, proanthocyanidin A2, syringic acid, p-hydroxybenzoic acid, poncirin, ferulic acid, rutin, phlorizin, and methyl hesperidin), purity ≥99%, were purchased from Shanghai yuanye biotechnology Co. Ltd. (Shanghai, China). Vitamin C; 1, 1-diphenyl-2-picrylhydrazyl (DPPH); 2, 2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS); 2, 3, 5-triphenyltetrazolium chloride (TPTZ); triton; tris-HCl; paraformaldehyde; and urethane were purchased from the Beijing Solaibao Technology Co. Ltd. (Beijing, China). Trizol reagent was purchased from TaKaRa (Beijing, China). Hematoxylin and eosin (H&E) kit, Oil Red O (ORO) kit, and a protein extraction kit were obtained from Beyotime Biotechnology (Beijing, China). Antibodies were purchased from Abcam (Shanghai, China).

Phenolic acid standards (gallic acid, p‐hydroxybenzoic acid, protocatechuic acid, vanillic acid, syringic acid, chlorogenic acid, caffeic acid, p‐coumaric acid, ferulic acid, and erucic acid) were purchased from Shanghai Yuanye Biotechnology (Shanghai, China). Other analytical pure reagents were obtained from Sinopharm Chemical Reagent (Shanghai, China).