Hydrophobicity exerts different effects on bioavailability and stability of antioxidant peptide fractions from casein during simulated gastrointestinal digestion and Caco-2 cell absorption

Alcalase-treated casein hydrolysates were separated into three hydrophobic chromatography fractions (HC-F1, HC-F2 and HC-F3) using YMC ODS C18 column. Simulated gastrointestinal (GI) digestion (stage I digestion) and Caco-2 cell absorption (stage II digestion) were sequentially applied for producing corresponding digests and adsorbates of collected peptide fractions. ANS probe and reverse-phase (RP)-HPLC were applied to detect peptide hydrophobicity, whereas trolox equivalent antioxidant capacity and oxygen radical antioxidant capacity were used to determine their antioxidant activity. Peptide nitrogen was used to evaluate bioavailability (BA) and remaining peptide content. In addition, RP-HPLC and electrospray ionization mass spectrometry were performed to obtain peptide sequences. Results showed that high hydrophobic peptide fractions (HC-F3) had excellent BA and remaining antioxidant activity, but poor digestive stability in stage I digestion. Two peptides, NTVP and IV, were identified from the adsorbate of HC-F3 to be GI-resistant peptides. Therefore, utilizing high hydrophobic peptides from casein as potential functional foods or nutraceuticals was feasible.