Kjeldahl tablets

Sodium hydroxide (NaOH), hydrochloric acid (HCl), trichloroacetic acid (TCA) and acetic acid were from Fisher Scientific (Dublin, Ireland). Kjeldahl tablets, sulfuric acid (>98%, H₂SO₄), boric acid, trifluoroacetic acid (TFA), Trizma^® base, dimethyl sulfoxide (DMSO), 2-mercaptoethanol, methanol, protein markers (6.5–200 kDa), Sudan III, 2,4,6-trinitrobenzenesulfonic acid (TNBS), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), porcine pepsin (2500 U/mg), porcine pancreatic lipase (50 mU/mL), 4-methylumbelliferyl oleate (4-MUO) and Orlistat^® were from Sigma-Aldrich (Dublin, Ireland). Hexane, MS-grade water and acetonitrile (ACN) were from Honeywell International Inc. (Dublin, Ireland). Comassie R, Laemmli buffer and Mini-Protean TGX 4–20% pre-cast polyacrylamide gels were from Bio-Rad Laboratories Inc. (Hercules, CA, USA). Sodium dodecyl sulfate (SDS) was from National Diagnostics (Atlanta, GA, USA). Corolase PP^® (4.4 U/mg) was from AB Enzymes GmbH (Darmstadt, Germany). Cellulose acetate filters were from Millipore (Carrigtwohill, Ireland) and polytetrafluoroethylene syringe filters were from VWR (Dublin, Ireland).

Chemicals and reagents were of analytical grade and acquired from Merck (Darmstadt, Germany) (Kjeldahl tablets, sulfuric acid, absolute ethanol, sodium carbonate decahydrate, sodium hydroxide, n-hexane and anhydrous sodium sulfate) and Sigma-Aldrich (St. Louis, MO, USA) (Folin–Ciocalteu’s reagent, gallic acid, catechin, heptahydrate ferrous sulfate, 2,2-diphenyl-1-picrylhydrazyl radical, 2,2′-azino-bis(3-ethylenbenzothiazoline-6-sulfonic acid, Trolox, ferric chloride, 2,4,6-tripyridyltriazine, sodium nitrite, aluminum chloride, sodium acetate, hydroxytyrosol and Supelco 37 FAME Mix). Boric acid 4% was purchased from Panreac (Barcelona, Spain) and methanol from Honeywell International, Inc. (Morris Plains, NJ, USA). Sodium chloride and chloroform were acquired from VWR Chemicals (Alfragide, Portugal). The tocopherol and tocotrienol standards and tocol were obtained from Calbiochem (La Jolla, CA, USA) and Matreya Inc. (State College, PA, USA), respectively. The solvents (HPLC grade) were acquired from Chem-Lab (Zedelgem, Belgium) or Merck (Darmstadt, Germany). A Milli-Q water purification system (Millipore, Bedford, MA, USA) was used to treat and obtain the ultrapure water.