Oxidation and Side-Chain Modification Decline Gastrointestinal Digestibility and Transport of Myofibrillar Proteins from Salted Bighead Carp Fillets after Frozen Storage

Abstract

This study examined the impact 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 intestinal membrane. The frozen fillets showed higher oxidation levels, reduced amino acid content, and lower in vitro protein digestibility, which was further accelerated 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 digested protein digestibility and influenced their intestinal transportation. These findings suggest that oxidation impacts protein digestion and should be considered in food processing and preservation strategies.

Keywords: Frozen storage, protein digestibility, Protein oxidation, Amino acid modification, Everted-rat-gut model