Rationale: Lipid oxidation has long been recognized as the major chemical reaction limiting shelf life and degrading quality of foods. In the past, the food industry has used partially hydrogenated oils and saturated fats to limit lipid oxidation, but current pressures to replace these oils with highly unsaturated ?healthy? oils readily oxidize now make it imperative to understand lipid oxidation reactions more fully to stabilize food systems, protect food sensory and nutritional qualities, and prevent formation of toxic products. Traditional theory explained lipid oxidation as free radical chain reactions that generate hydroperoxides and alcohols by hydrogen abstraction and secondary products by scission. However, evidence suggests that lipid peroxyl radicals (ROO.) and alkoxyl radicals (RO.) also undergo independent rearrangement, addition, and elimination reactions in addition to hydrogen abstractions in early stages of the radical chain reactions. These alternative reactions can dominate under conditions commonly occurring in foods and dramatically change lipid oxidation in complex ways. This project initiates fundamental studies of how these multiple pathways alter the kinetics, products, detectability, and consequences of lipid oxidation (e.g. development of off-flavors and odors, tendency to brown, reactions with other molecules leading to texture deterioration, changes in surface activity, formation of toxic products, loss of nutritional value). Methods: Products and quality consequences associated with each pathway, as well as how oxygen pressure, temperature, lipid concentration and solvent drive reactions and products in different directions will be measured in methyl linoleate as a simple model lipid system. Lipid free radicals will be monitored by electron paramagnetic resonance; oxidation products will be identified and quantified by gas chromatography (volatile) and high pressure liquid chromatography (non-volatile) with mass spectrometry detection. Outcomes: Data identifying both volatile and non-volatile lipid oxidation products generated when methyl linoleate oxidizes under a range of conditions will be systematically integrated to provide a new road map for lipid oxidation and a solid data base to guide subsequent studies of more unsaturated and structurally more complicated lipids in oils and complex food systems. Anticipated benefits: This new knowledge will be critical for optimally stabilizing foods formulated with n-6 essential and n-3 polyunsaturated fatty acids and for protecting both sensory qualities and nutritional value. Applying this fundamental research long term will facilitate development of lipid oxidation analyses that more accurately reflect all pathways of oxidation; more effective extension of shelf-life through modifications of processing, packaging, antioxidant use, and storage; and creative opportunities to deliberately control dominant pathways in individual food systems, e.g. balances between desirable and unwanted flavor compounds, between flavor and polymerization / viscosity changes, between carbonyls that may contribute to browning and epoxides that are toxic and react rapidly with proteins.
|Effective start/end date||8/15/08 → 8/15/11|
- National Institute of Food and Agriculture (National Institute of Food and Agriculture (NIFA))