Gallic acid

Epicatechin, kaempferol, quercetin, rutin, isoquercitrin, syringic acid, p-coumaric acid, chlorogenic acid, cryptochlorogenic acid, caffeic acid, ferulic acid and gallic acid were purchased from Adamas Reagent, Ltd. (Shanghai, China). Other standard reference materials including 4-methoxysalicylic acid, p-hydroxycinnamic acid, isoferulic acid, 1,3-dicaffeoylquinic acid, gentiopicrin, grosvenorine, diosmin, isorhamnetin and baicalein were obtained from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). 2,4,6-tri(pyridin-2-yl)-1,3,5-triazine (TPTZ), 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS), 4-nitrophenyl α-D-glucopyranoside (p-NPG) were all obtained from Adamas Reagent, Ltd. (Shanghai, China). Acetonitrile and formic acid (99.9%, HPLC grade) were obtained from Thermo Fisher Scientific (Waltham, MA, USA). Cellulase (400 u/mg) from Trichoderma Vride G, hemiCellulase (20,000 u/g) and pectinase (500 u/mg) from Aspergillus niger were all supplied from Shanghai Yuanye Bio-Technology Co., Ltd. (Shanghai, China). All other reagents and chemicals used in this study are analytical grade.

Eight standards were used in this work: gallic acid, caffeic acid, luteolin were purchased from Adamas Reagent (Shanghai, China); acacetin was purchased from TCI (Tokyo, Japan); apigenin was purchased from WAKO Pure Chemical Industries (Osaka, Japan); protocatechuic acid, ferulic acid, and hesperidin were purchased from Sigma-Aldrich (MO, USA). Acetonitrile and formic acid in HPLC grade were purchased from Fisher Chemical (Geel, Belgium). Ethanol and acetic acid in AR grade were purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). Folin-Ciocalteu and Na₂CO₃ were purchased from Sigma-Aldrich (MO, USA).
Flower of D. indicum var. aromaticum was harvested in Shen Nongjia area of Hubei province, China. The plant species was identified by Prof. Keli Chen, Hubei University of Chinese Medicine, and authenticated by Herbarium, Kunming Institute of Botany, Chinese Academy of Sciences. The certificate of plant material authentication was provided as Supplementary. Plant material was harvested freshly, and spread at a shady, cool and well-ventilated place to dry naturally. Dry material was kept in −80 °C freezer before using.