Sodium hydrogencarbonate

All chemicals and reagents used in the experiments were of per analysis and HPLC grade. Folin–Ciocalteu reagent, potassium chloride, sodium hydrogencarbonate, potassium hydrogenphosphate, magnesium chloride hexahydrate, sodium chloride, ammonium carbonate, sodium hydroxide, and petroleter were supplied from Kemika d.d. (Zagreb, Croatia). Anhydrous sodium carbonate and sodium nitrite were acquired from Gram-Mol d.o.o. (Zagreb, Croatia). Sodium molybdate (>98%) was supplied from abcr Gmbh (Karlsruhe, Germany). Methanol, acetonitrile, concentrated hydrochloric acid (37%, v/v), sodium hydroxide, and formic acid were purchased from Carlo Erba Reagents (Val de Reuil, France). Secondary analytical standards, i.e., echinacoside (>98%) and verbascoside (>98%), were obtained from Biosynth s.r.o. (Bratislava, Slovakia), whereas caffeine was supplied from Fluka (Taufkirschen, Germany). Theobromine (min. 99%), human salivary α–amylase XII-A (Enzyme Commission number: 3.2.1.1.; 1149 U mg⁻¹ protein), pepsin from porcine gastric mucosa (474 U mg⁻¹ protein), pancreatin from porcine pancreas (4×USP), and bile bovine salts (unfractionated) were provided from Sigma Aldrich (St. Louis, MO, USA).

Edible sunflower oil (Zvijezda, Zagreb, Croatia) was bought in a supermarket. Waste cooking oil (WCO) used in this research was collected after deep frying of potatoes. F.A.M.E. mix GLC-10, the commercial lipase from Thermomyces lanuginosus (Lipolase 100L), isoamyl alcohol, iso-octane and sodium dodecyl sulfate (SDS) were purchased from Sigma-Aldrich Handels GmbH (Vienna, Austria). Chloroform and acetonitrile were purchased from Fisher Chemicals (Loughborough, United Kingdom). Tris (hydroxymethyl) aminomethane (TRIS), methanol, HCl and n-heptane were purchased from BDH Prolabo (VWR, London, United Kingdom). Dipotassium hydrogen phosphate (K₂HPO₄) and ammonium sulfate were purchased from Merck (Darmstadt, Germany). KOH and potassium dihydrogen phosphate (KH₂PO₄) were purchased from Lach:ner (Prague, Czech Republic). Sodium hydrogen carbonate was purchased from Kemika (Zagreb, Croatia). 4-nitrophenyil-acetate was purchased from Acros Organics (Fischer Scientific, Geel, Belgium).