Stability of casein antioxidant peptide fractions during in vitro digestion/Caco-2 cell model: characteristics of the resistant peptides

Peptides with in vitro antioxidant activity have no direct reaction on in vivo organisms, because of gastrointestinal (GI) barriers in human tract. In this study, low-molecular-weight peptides of casein were acquired by hydrolysis with alcalase and isolation with Sephadex G-25 gel filtration. Each peptide fraction was performed on simulated GI digestion (stage I) and Caco-2 cell absorption (stage II) for evaluating GI stability, with molecular weight distribution, peptide nitrogen, trolox equivalent antioxidant capacity, and oxygen radical antioxidant capacity. The peptide fraction below 1,000 Da (F3) had shown weaker structural stability during stage I digestion, while it exerted excellent antioxidative stability in whole stages and finally produced the highest content of GI resistant peptides. Three resistant peptides, Ile-Glu, Ser-Asp-Lys, and Ala-Tyr-Pro-Ser, were characterized, and Ala-Tyr-Pro-Ser might strongly contribute to in vivo antioxidant activities. It is suggested that alcalase may promote the production of GI resistant peptides.