Food-derived antioxidant peptides undergo oxidative transformations that may alter their function and safety

Bioactive peptides used in foods and nutraceuticals are frequently exposed to oxidizing environments that reshape their structure, function, and safety profile. Beyond acting as radical scavengers, peptides can undergo extensive modification by reactive oxygen species (ROS) and by oxidized lipid and sugar products that co-occur in complex food matrices. Mechanistic studies reveal that hydroxyl radicals, peroxyl radicals, and metal‑catalyzed H₂O₂ systems generate peptide hydroperoxides, carbonyls, backbone fragments, and covalent dimers in a sequence‑dependent manner, particularly at proline, tryptophan, tyrosine, and histidine residues. Parallel reactions with oxidized lipids, including lipid hydroperoxides and electrophilic aldehydes such as malondialdehyde and hydroxynonenal, drive additional layers of modification through trans‑oxidation, Schiff base formation, and Michael addition, yielding diverse adducts whose structures and stabilities differ markedly from classical ROS products. Glycation and glycoxidation further contribute carbonyl‑derived cross‑links and fluorophores in sugar‑rich systems. While the biological consequences of protein oxidation are well described, the functional and toxicological implications of oxidized bioactive peptides remain largely unexplored. Emerging evidence indicates that peptide hydroperoxides, lipid‑derived aldehyde adducts, and advanced glycoxidation/lipoxidation products can alter peptide bioavailability, immunoreactivity, redox behaviour, and cellular functions in cell and animal models. This review integrates current knowledge on the chemistry, analytical detection, and structural diversity of peptide oxidation products, highlights sequence‑specific reactivity patterns, and outlines safety considerations and research priorities for peptide‑based functional ingredients.