2.1. Plant material and chemicals

Orange (Citrus sinensis) and lemon (C. limon) peels were obtained from Biopower Technologies Limited (BioPower, UK). Mandarin (C. reticulata) peel was obtained from Xiangshan Huayu Foodstuffs Co. Ltd (China). The peels were diced, dried at 65 °C and then micronized to particle size of < 150 µm. All the samples were packed in polythene bags and stored at −20 °C until needed.

Amberlite (R) XAD-7HP resin (20–60 mesh), Folin-Ciocalteu, Na₂CO₃, gallic acid, and sodium acetate were purchased from Sigma (UK). Ethanol was procured from VWR (USA). AlCl₃ was purchased from Honeywell (USA). tert-Butylhydroquinone (TBHQ) was from Aldrich. Dimethyl sulfoxide (DMSO) was from Fluorochem (UK). Milli-Q water was used for extraction. Reagents used in HPLC analysis were of analytical grade. Formic acid, acetonitrile was purchased from Merck Life (UK). HPLC grade standards (purity > 97%) were used. Naringenin narirutin, naringin, hesperetin, hesperidin, neohesperidin, quercitrin, rutin, isorhoifolin, rhoifolin, luteolin, cymaroside, didymin, poncirin, eriodictyol, eriocitrin, neoeriocitrin, isorhamnetin, diosmetin, neodiosmin, sinensetin, tangeretin, taxifolin, nobiletin, and protocatechuic acid were purchased from Extrasynthese (France). Quercetin, p-coumaric acid, chlorogenic acid, ferulic acid and gallic acid were obtained from Sigma (UK). Apigenin was purchased from PhytoLab (Germany), p-hydroxybenzoic acid from SΛFC (USA), vanillic acid from Alfa Aesar (USA), and caffeic acid from Cayman Chemical (USA).