Lipid co-oxidation of functional biomolecules: The case for looking beyond lipids in oxidative degradation of foods, pet foods, and biological tissues

     That oxidizing lipids react with and co-oxidize other molecules in foods and biological tissues has been recognized for more than 50 years now, yet the phenomenon is still not fully accepted as an important action compared to the rancid off-odors and flavors produced by lipids alone. Starting from a handful of papers documenting structural degradation plus loss of enzymatic activity and nutritional value in proteins caused by reaction with lipid radicals and secondary oxidation products, the co-oxidation field has expanded to thousands of papers that include not just proteins, but chemical, structural, and functional modifications of starches, vitamins, phenolic compounds, pigments, nucleic acids, and other biomolecules by oxidizing lipids as well. Accumulated data now shows clearly that oxidative degradation may originate with lipids but is broadcast from them to affect the entire system, replacing typical lipid oxidation products with currently unmonitored changes in other molecules. Under such conditions, system oxidation state cannot be evaluated accurately by lipid peroxide values and sensory volatile products alone.

     This paper reviews the general mechanisms by which oxidizing lipids co-oxidize other molecules, the types of damage resulting in important biomolecules, how this damage translates into functional modifications physiologically and in foods, and how co-oxidations impact food, nutritional, and health quality beyond simple oxidation of lipids. Using this information, arguments will be presented for viewing oxidation as a systemic issue rather than merely a lipid problem, for including co-oxidation measures to monitor the state of system oxidation rather than just the extent of lipid oxidation, and for integrating control of co-oxidations into design of formulations and processing.