The absorbates of positively charged peptides from casein show high inhibition ability of LDL oxidation in vitro: Identification of intact absorbed peptides

Resistance to gastrointestinal (GI) digestion and absorption is necessary for bioactive peptides to exert their biological activities. In this study, casein hydrolysate was separated into four fractions according to the charge property. After simulated GI digestion and Caco-2 cell absorption, the cellular antioxidant activity (CAA) and inhibition of LDL oxidation of peptide absorbates (PA) were investigated. The PA of positively charged fractions exhibited higher CAA and inhibition of LDL oxidation than negatively charged fractions. The peptide sequences from the digest and PA of the positively charged fractions were identified using UPLC-ESI-qTOF-MS. By comparing the amino acid sequences, 35 intact absorbed peptides (IAPs) were identified. Three IAPs were synthesized and all were verified to be IAPs, which significantly inhibited LDL oxidation. The overall positive charge property of peptides may play an important role in their ability to inhibit LDL oxidation, and IAPs may have real antioxidative efficacy in vivo.