Oxidation and side-chain modifications decrease gastrointestinal digestibility and transport of proteins from salted bighead carp fillets after frozen storage.

• Protein digestibility decreased in brined fillets after 6 months of frozen storage. • Nutritional attributes decreased with the increase in protein oxidation levels. • Degradation of peptide at the site adjacent to modified amino acids was inhibited. • Malondialdehyde adduct was responsible for inhibited protein intestinal transport. This study examined the effects of protein oxidation on digestion behavior. The oxidation levels and in vitro digestibility of myofibrillar proteins from fresh-brined and frozen bighead carp fillets were investigated, and the intestinal transport property was characterized by comparing the peptides on both sides of the intestinal membrane. Frozen fillets showed high oxidation levels, low amino acid content and in vitro protein digestibility, which were further increased by brining. After storage, the number of modified peptides from myosin heavy chain (MHC) increased over 10-fold in NaCl-treated samples (2.0 M). Various types of side-chain modifications in amino acids were identified, such as di-oxidation, α-aminoadipic semialdehyde (AAS), γ-glutamic semialdehyde (GGS), and protein-malondialdehyde (MDA) adducts, mainly originating from MHC. The Lysine/Arginine-MDA adducts, AAS, and GGS decreased protein digestibility and their intestinal transportation. These findings suggest that oxidation impacts protein digestion and should be considered in food processing and preservation strategies. [ABSTRACT FROM AUTHOR]