Oxidation of proteins

Abstract The most common consequences of protein oxidation include dimerization through cross-linking, modification of amino acid side-chain, and protein fragmentation. Amino acids with side-chains most prone to oxidative modification are the sulfur-containing amino acids Cys and Met, the aromatic amino acids Trp, Tyr, and Phe, as well as His, Pro, Lys, and Arg. Several factors are known to trigger protein oxidation reactions including reactive oxygen species and nonradicals. Protein oxidation often goes hand in hand with lipid oxidation; for example, lipid hydroperoxides can initiate protein oxidation. Carbonyls are generally used as markers of protein oxidation although carbonyls are derived only from Lys, Agr, and Pro. However, there is no universal analytical method to monitor protein oxidation. Protein oxidation in foods leads to impaired food functionalities, reduction of nutritional value, and changes in physiological functions. Thus controlling the conditions for processing and storage of protein-rich food and food ingredients is important. Protein oxidation may also be purposely employed for improved food structure, as for example enzymatic cross-linking of Cys and Tyr residues. The present chapter provides an overview of the consequences of protein oxidation in both animal-based and plant-based raw materials and products.