Interplay between protein oxidation and lipid peroxidation in food systems

Abstract: Both lipids and proteins undergo oxidation during food production, processing, and storage; however, the extent of oxidation depends on their concentration, availability to oxidants, and rate constants for the reaction. In food science, the chemistry and consequences of lipid oxidation have been studied more than protein oxidation due to its unique association with ‘rancid off-flavor’. However, recent studies show that proteins (not lipids) are the primary targets for oxidants due to higher rate constants for the reaction. Furthermore, proteins and lipids coexist in most food products; thereby, radicals, hydroperoxides, and reactive carbonyl species formed during lipid peroxidation can irreversibly damage proteins. Such reactions lead to the degradation of essential amino acids, formation of protein-carbonyl adducts (protein lipoxidation), loss of solubility, protein crosslinking, and loss of nutritional value. On the other hand, proteins prevent lipid peroxidation and off-flavor formation through antioxidant and carbonyl-scavenging properties of their amino acid residues (e.g., Cys, His, and Met). However, little is known about such interplay between protein oxidation and lipid peroxidation, as it is difficult to distinguish protein modification induced by other competitive chemical reactions in foods (e.g. caramelization and the Maillard reaction) and the analytical challenges of determining detailed protein modifications. To improve knowledge of protein oxidation and protein lipoxidation in food systems, we have developed an LC-MS/MS-based analytical toolbox and investigated protein medications in different food products, including milk, meat and fish. Our methods can selectively quantify over 30 different protein oxidation products, reactive carbonyl species, and lipoxidation end-products with a sensitivity in the nanomolar range. Such analytical toolboxes could be used with studies on the co-oxidation of proteins and lipids. Overall, this presentation provides an overview of protein oxidation and how lipid oxidation products induce protein modification in foods by drawing knowledge from the literature and our multiple research projects.