Folin ciocalteu phenol reagent

Green, black, and oolong tea (Granum Inc., Seattle, WA, USA) were purchased from the local supermarket (Amherst, MA, USA). Corn starch, casein, vitamin mix, mineral mix, calcium phosphate and sodium chloride were purchased from Raon Bio (Yongin, Korea). Blood glucose analyzer was purchased from Caresens (I-SENS, Anyang, Korea). 2,2-Diphenyl-1-picrylhydrezyl was purchased from Alfa Aesar. (Ward Hill, MA, USA). Folin-Ciocalteu phenol reagent, rat intestinal acetone powders, 4-nitrophenyl α-d-glucopyranoside, o-Dianisidine dihydrochloride, glucose oxidase/peroxidase reagents were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). Unless noted otherwise, all chemicals were purchased from Fisher Scientific Company Co. (Bridgewater, NJ, USA).

The total phenolic content of OA extract was determined by using the Folin-Ciocalteu colorimetric method. In brief, 1000 μl of a 50% Folin-Ciocalteu phenol reagent (Sigma-Aldrich, USA) and 158 μl of distilled water were mixed with 20 μl of the tested substances (OA extract and gallic acid) and incubated at 37°C for 8 minutes. At the end of the incubation period, 30 μl of 20% Na₂CO₃ (Sigma-Aldrich, USA) was added, mixed, and incubated at room temperature in the dark room for 2 hours. Then, the absorbance at 765 nm was recorded. Results were expressed as mg gallic acid equivalent (GAE)/mg per 0.1 g of OA extract. Various concentrations of gallic acid (Sigma-Aldrich, USA) ranging from 0 to 500 μg/ml were used to prepare the standard calibration curve [26 (link)].

Coconut (Cocos nucifera) sample was collected from the local market of Hyderabad (Figure 1). The 2,2-diphenyl-1-picrylhydrazyl (DPPH), Folin-Ciocalteu phenol reagent, sodium carbonate and gallic acid were purchased from Sigma-Aldrich (St. Louis, MS, USA). Dextrose agar and all other chemicals and reagents were used of analytical grade. The solution preparations were made using double distilled water. The absorbance was evaluated using the lambda 35 UV-Vis spectrophotometer (Perkin Elmer, Richmond, VA, USA).

All chemicals and reagents used in this study were of analytical grade unless stated otherwise. Trolox, gallic acid, Folin–Ciocalteu phenol reagent, 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), and 2,4,6-tris (2-pyridyl)-s-triazine (TPTZ) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Standard compounds such as hydroxytyrosol, esculin, taxifolin, luteolin, quercetin, kaempferol, apigenin, chlorogenic acid, plantamajoside, rutin, eriodictyol, tiliroside, apigenin-7-O-neohesperidoside, apigenin-7-O-glucoside, luteolin-7-O-glucoside, oleuropein, secoxyloganin, asiatic acid, oleanonic acid, maslinic acid, corosolic acid, oleanolic acid, and ursolic acid were purchased from Yuanye Bio-Technology Co., Ltd. (Shanghai, China). For chromatography analysis, HPLC-grade acetonitrile and acetic acid were purchased from Merck (Darmstadt, Germany) and Alfa Aesar (Shanghai, China), respectively. Ultrapure water supplied by a Milli-Q system (Millipore, Bedford, MA, USA) was used throughout the experiments.

Aerial parts of Sideritis raeseri subsp. raeseri were collected in the phase of full flowering (July, 2019) on the natural locality of Sreden Vrv (altitude 1600–1660 m), Galičica mountain, North Macedonia. Voucher specimens Nos. S31/16–S33/16 were deposited at the Institute for Medicinal Plants Research, Belgrade, Serbia. Plant material was air-dried at room temperature for 4–6 days and ground using a laboratory mill. Following standards previously isolated and identified in our laboratories, the following were used: 4′-O-methylhypolaetin-7-O-[6‴-O-acetyl-β-d-allopyranosyl (1→2)]-β-d-glucopyranoside (HYP), isoscutellarein 7-O-[6‴-O-acetyl-β-d-allopyranosyl-(1→2)]-β-d-glucopyranoside (ISC 1), and 4′-O-methylisoscutellarein-7-O-[6‴-O-acetyl-β-d-allopyranosyl-(1→2)]-β-d-glucopyranoside (ISC 2) [2 ]. All reagents used for analytical procedures were of analytical grade: Folin–Ciocalteu phenol reagent, sodium carbonate, methanol, orthophosphoric acid, and formic acid were purchased from Sigma-Aldrich Chemie GmbH (Munich, Germany), while HPLC grade acetonitrile was purchased from Merck (Germany).

Viscum articulatum Burm. f. (CMC) and Viscum liquidambaricolum Hayata (CMP) were purchased from Pu’er, Yunnan province, China in 2016. Standard phenolic compounds (gallic acid, protocatechuic acid, chlorogenic acid, caffeic acid, p-coumaric acid, (−)-epigallocatechin, myricetin, kaempferol, apigenin, epicatechin, quercetin, vanillic acid, syringic acid, trans-cinnamic acid, catechin, ferulic acid, p-hydroxybenzoic acid and vanillin) were purchased from Beijing Beina Chuanglian Biotechnology Institute (Beijing, China). Folin-Ciocalteu phenol reagent, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), 2,2-diphenyl-1-picrylhydrazyl (DPPH) were obtained from Sigma-Aldrich (St. Louis, MO, USA). 2,4,6-Tripyridyl-s-triazine (TPTZ), 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), trichloroacetic acid, ferric chloride, ascorbic acid, ferrous sulfate, potassium ferricyanide, sodium phosphate dibasic, sodium phosphate monobasic dihydrate, H₂O₂, aluminum chloride and potassium persulfate were purchased from Aladdin Industrial Corporation (Shanghai, China). HPLC-grade methanol and formic acid were purchased from Merck (Darmstadt, Germany). All chemicals used in the experiments were of analytical grade.