Most attention for food safety and stability currently focuses on microbial contamination and inactivation. However, once bacteria, yeasts, and molds have been eliminated, chemical oxidation of lipids and proteins become the major drivers of degradation in foods with loss of sensory quality and nutritional value during storage and with potential generation of toxic products. Lipid and protein oxidation are also intimately involved in many pathologies in vivo, including aging, atherosclerosis, Alzheimer's disease, and cancer. Thus, understanding lipid and protein oxidation reactions and being able to control these processes is critically important for health, for stabilizing foods, for reducing food costs and food losses, and for maintaining food safety. Oxidation problems were largely ignored during the no/low fat food era, but new recognition of important roles of lipids in health is forcing reformulation of foods with higher contents of polyunsaturated fatty acids. These physiologically essential fatty acids are highly oxidizable in themselves and they cause extensive co-oxidation of other food molecules, particularly proteins.Unfortunately, basic information about how lipids and proteins oxidize is outdated and incomplete so stabilization efforts in the food industry have encountered many hurdles. Stabilization problems are complicated further by current pressure to eliminate synthetic antioxidants such as BHT and replace them with natural antioxidants. Here again, information about how natural antioxidants act in complex systems such as foods is rather limited. This program addresses these deficits and seeks to provide a broad base of fundamental information about how lipids and proteins oxidize and how natural antioxidants act. While focused on food degradation and stabilization, the chemistry elucidated is applicable also to toxicology, medicine, plant physiology and pathology, and personal products and cosmetics industries.Five different research areas are active to provide this fundamental information. The cornerstone project applies a wide range of chemical and instrumental analyses, including high pressure liquid chromatography and gas chromatography to separate products and mass spectrometry to identify lipid oxidation product structures in test oils and lipids extracted from foods. Monitoring oxidation rates and products under different conditions shows us how food formulation and environment alters active oxidation pathways, which in turn controls food quality, safety, and nutrition. Heat degradation of oils is studied in an oxygen bomb that provides very precise temperature and atmospheric gas and pressure and allows removal of both oil and headspace for following degradation of the oil over time at different temperatures. This system models frying operations and the information gained will be very useful in designing new processes to limit breakdown of oil and production of toxic products during frying as well as stabilizing fried foods during storage. Near infra-red spectroscopy and nuclear magnetic resonance are used to detect multiple products simultaneously. Protein oxidation occurring in different foods is determined by chemical assays for solubility and formation of specific oxidation products from individual amino acids; by polyacrylamide gel electrophoresis to detect protein polymerization, fragmentation, and rearrangements; by antibody reactions to quantitate carbonyl oxidation products; and by enzymatic digestion followed by high pressure liquid chromatography-mass spectrometry analysis of modified amino acids. Comparisons show that patterns of damage and effects on food properties are not common but vary with the type of protein and the food matrix. Simultaneous analysis of lipid and protein oxidation in the same food reveal extensive connections between these two processes. Following lipid and protein oxidation in foods and biological systems requires analyses that detect very low levels of a large number of products accurately and specifically. Many assays commonly used lack sensitivity or specificity or are too general, and many oxidation products have no good assays. Thus, a fourth important research focus is to re-evaluate existing lipid oxidation assays and develop new assays that can detect and quantitate more detailed oxidation products from both lipids and proteins. These new assays are critical for providing the puzzle pieces from which new understanding of oxidation mechanisms will be built. Finally, the fifth research area seeks to limit oxidation and improve stabilization of foods by learning more about how natural antioxidants stop oxidation of lipids and proteins, how they partition between oil and aqueous phases of foods and biological tissues and how their actions may differ in the two phases, and how the complex structures and composition of foods enhances or impairs their antioxidant effectiveness. These tests use DPPH (diphenylpicrylhydrazyl) and ORAC (oxygen radical antioxidant capacity) assays to distinguish active radical quenching mechanisms, conjugated diene and oxygen consumption assays to track oxidation in oils and emulsions, and conjugated diene, hydroperoxide, and carbonyl assays to determine oxidation in model foods. Integration of information from the different tests provides a means of predicting which natural antioxidants will be effective in foods and provides guidelines for using specific natural antioxidants in different food systems.Results not applied remain just data. Thus, the ultimate goal is to use the integrated results from these projects to learn how best to analyze lipids and proteins to most accurately assess their true extent of oxidation and degradation, to recognize oxidation earlier, to develop strategies that more effectively limit oxidation and control active oxidation pathways for both lipids and proteins, and to provide foods that taste good, retain desirable textures and colors during storage, and maintain safety and nutritional quality over longer periods of time.
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