4 hydroxybenzoic acid

Dehulled seeds of organic black quinoa (Chenopodium quinoa Willd.), labelled as originating from Bolivia (South America) and packed in a protective atmosphere, were purchased in a retailer specialized in organic and biodynamic products in Italy. Proximate composition per 100 g was, as reported in the nutrition label: 380 kcal energy; 6.2 g fat, of which 0.7 g saturates; 65 g carbohydrates, of which 4.0 g sugars; 9.0 g fibre; 12 g protein; and 0.01 g salt.
Folin–Ciocalteu’s Reagent, methanol, ethanol, acetone, acetic acid and acetonitrile were purchased from Carlo Erba Reagents (Milan, Italy).
Caffeic acid, (+)-catechin, o-coumaric acid, p-coumaric acid, (−)-epicatechin, 3,4-dihydroxycinnamic acid, t-ferulic acid, gallic acid, gentisic acid, 4-hydroxybenzoic acid, protocatechuic acid, rutin, sinapic acid, syringic acid, vanillic acid, and vanillin were purchased from Extrasynthèse (Geney, France) and Sigma-Aldrich (St. Louis, MO, USA).
HPLC grade solvents and water purified by a Milli-Q system (Millipore Corp., Billerica, MA, USA) were used in HPLC analysis.

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).

All solvents used (methanol, acetonitrile, acetic acid, water and ethyl acetate) were HPLC-grade and were purchased from Merck (Darmstadt, Germany). Protocatechuic acid, 4-hydroxybenzoic acid, vanillic acid, chlorogenic acid, trans-p-coumaric acid, eriodictyol-7-O-glucoside, eriodictyol, naringenin, naringenin-7-O-glucoside, kaempferol-3-O-rutinoside, kaempferol-3-O-glucoside, isorhamnetin-3-O-glucoside, quercetin, kaempferol, isorhamnetin, quercetin-3-O-rutinoside, quercetin-3-O-galactoside, quercetin-3-O-glucoside, isorhamnetin-3-O-rutinoside, catechin and epicatechin were purchased from Extrasynthese (Genay, France). Other chemicals were of analytical grade.