Isovanilic acid

The following HPLC- or LC-MS-grade reagents were used for analyses: acetonitrile, L-ascorbic acid, methanol (Sigma-Aldrich, Poland), acetic acid (Baker, Poland), and formic acid (VWR Int., Poland). The qualitative and quantitative content of polyphenolic compounds was determined with the following standards: 3,4-dihydroxybenzoic acid, 4-hydroxybenzoic acid, chlorogenic acid, caffeic acid, gallic acid, isovanilic acid, kaempferol, luteolin, neochlorogenic acid, orientin (luteolin-8-glucoside), p-coumaric acid, procyanidin B2, quercetin, quercetin-3-O-glucoside (Sigma-Aldrich, Poland), (+)-catechin, (–)-epicatechin, quercetin-3-O-galactoside, quercetin-3-O-rutinoside, quercetin-3-O-vicianoside (Extrasynthese, France), cyanidin-3-O-arabinoside, cyanidin-3-O-galactoside, cyanidin-3-O-glucoside (Polyphenols Laboratories AS, Norway) and cyanidin-3-O-xyloside (Toronto Research Chemicals, Canada).

Chemical reagents (acetonitrile, L-ascorbic acid, methanol, acetic acid, and formic acid) were purchased from Sigma-Merck, Poznań, Poland. For the qualitative and quantitative content of polyphenols the following standards were used: gallic acid, caffeic acid, isovanilic acid, chlorogenic acid, neochlorogenic acid, p-coumaric acid, 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, orientin (luteolin-8-glucoside), quercetin, quercetin-3-O-glucoside, procyanidin B2, luteolin, kaempferol (Sigma-Aldrich, Poznań, Poland), cyanidin-3-O-glucoside, cyanidin-3-O-galactoside, cyanidin-3-O-arabinoside (Polyphenols Laboratories AS, Sandnes, Norway), cyanidin-3-O-xyloside (Toronto Research Chemicals, North York, ON, Canada), quercetin-3-O-galactoside, quercetin-3-O-vicianoside, quercetin-3-O-rutinoside, (+)-catechin and (−)-epicatechin (Extrasynthese, Genay, France). All other chemicals were of analytical grade.

Thermostable α-amylase (Novozymes, Bagsvaerd, Denmark) was used for digestion of starch. The reagents used to determine the content of neutral detergent fiber (NDF) were: sodium dodecyl sulfate (C₁₂H₂₅NaO₄S, Sigma-Aldrich, Saint Louis, USA), neutral disodium versenate dehydrate (C₁₀H₁₄N₂Na₂O_8*10H₂O), disodium tetraborate decahydrate (Na₂B₄O₇*10 H₂O), disodium hydrogen phosphate (Na₂HPO₄) and ethylene glycol (Poch, Gliwice, Poland). Reagents used to determine the content of ADF were 1 N sulfuric acid (H₂SO₄, 1 N, Poch, Gliwice, Poland) and N-cetyl-N,N,N-trimethylammoniumbromid (C₁₉H₄₂BrN, Merck, Darmstadt, Germany). Reagents used to determine the content of ADL were: sulfuric acid (72%), and acetone (Poch, Gliwice, Poland). Determination of polyphenolic contents was performed using the reagents and standards of acetonitrile, methanol, 2,6-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 3,5-dihydroxybenzoic acid, 4-hydrobenzoic acid, caffeic acid, catechin, chlorogenic acid, fagopyrin, ferulic acid, myricetin, gallic acid, isovanilic acid, isovitexin, kaempferol, luteolin, p-coumaric acid, procyanidin B2, quercetin, quercetin 3-D galactoside, rutin, syringic acid and vitexin, purchased from Sigma Aldrich (Steinheim, Germany).