Naringenin

Acetonitrile (99.9%) was of HPLC grade from Fisher Scientific (Lisbon, Portugal). Phenolic compound standards (chlorogenic acid, ferulic acid, naringenin, p-coumaric acid, quercetin-3-O-glucoside, quercetin-3-O-rutinoside, and taxifolin) were from Extrasynthèse (Genay, France). Formic acid was purchased from Sigma-Aldrich (St. Louis, MO, United States). All other general laboratory reagents were purchased from Panreac Química S.L.U. (Barcelona, Spain). Water was treated by using a Milli-Q water purification system (TGI Pure Water Systems, Greenville, SC, United States). Ferric chloride; 6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox) (97%); diammonium 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) (>98%); 2,2-diphenyl-1-(2,4,6-trinitrophenyl) hydrazine (DPPH); 2,4,6-tris (2-pyridyl)-s-triazine (TPTZ) (≥99%); dimethyl sulfoxide (DMSO) (≥99%); phosphate buffer, mushroom tyrosinase; 3,4-dihydroxy-l-phenylalanine (l-DOPA) (≥98%); and kojic acid were purchased from Sigma (Sigma-Aldrich Chemie GmbH, Schnelldorf, Germany). All other reagents used, including solvents, were of analytical grade.

Kaempferol (96%) and formononetin (99%) were
purchased from Fluka(Brøndby, Denmark). Biochanin A (97%), genistin
(95%), nicotiflorin (98%), and astragalin (99%) were purchased from
Sigma-Aldrich (Brøndby, Denmark). Hyperoside (99%) was purchased
from Roth (Karlsruhe, Germany). Daidzein (97%) and genistein (97%)
were purchased from Lancaster (Brønshøj, Denmark). Rutin
(99%), apigenin (99%), naringenin (99%), and daidzin (90%) were purchased
from Extrasynthese (Genay, France). Medicarpin was obtained from Dr.
Paul M. Dewick at the University of Nottingham, UK. Quercetin-rha-xyl-gal
was isolated from white clover, purified, and identified by its UV,
mass, and nuclear magnetic resonance spectra as part of a previous
study.^{14 (link)}Stock flavonoid solutions
of 1 g·l^–1 were prepared by dissolution in
methanol. Working standard solutions of the compounds were obtained
by serial dilution of the stock standard solutions in 35% MeOH and
65% Milli-Q water (v/v) containing 0.2% formic acid. Mixed standard
curves for the negative and positive modes were generated from 10
concentrations of each standard and used for quantification.

The standard compounds and reagents (all of analytical grade): MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), DMSO (dimethyl sulfoxide), gallic acid, Na₂CO₃, 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), Folin-Ciocalteu’s reagent, resazurin, tetracycline, chloramphenicol, kanamycin, acetonitrile (LC-MS grade, gradient grade), formic acid, 4-methoxybenzoic acid, 4-hydroxy-3-methoxycinnamaldehyde, caffeic acid, quercetin, luteolin and pinostrobin PBS were purchased from Merck (Darmstadt, Germany). The standards of 4-hydroxybenzoic acid, p-coumaric acid, ferulic, isoferulic acid, pinobanksin, chrysin, sakuranetin, naringenin, apigenin, kaempferol, isorhamnetin, acacetin and pinocembrin were obtained from Extrasynthese (Genay, France) and galangin from Alfa Aesar, (Haverhill, MA, USA). The antibiotics: ampicillin, oxacillin, teicoplanin, gentamicin, amikacin, fusidic acid, erythromycin, mupirocin, rifampicin, levofloxacin, norfloxacin, linezolid, bacitracin were purchased from Argenda (Poland). Methanol, ethanol, vanillin, benzoic acid, cinnamic acid were purchased from (POCH, Gliwice, Poland). Ultrapure H₂O (18.0 MΩ) was obtained with a Milli-Q Advantage A10 system (Millipore, Billerica, MA, USA). The absorbance of the reaction mixture in Folin-Ciocalteu, DPPH assays were measured using a Genesys 20 spectrophotometer (Thermo Scientific, Waltham, MA, USA).