| Lipid oxidation is recognized as the greatest problem in chemical stabilization of processed foods during storage. Lipid co-oxidations caused by reactions of lipid oxidation intermediates and products with other molecules, particularly proteins, are known, but their impact on food quality (production of off-flavors and odors, loss of color and nutritional value, and texture deterioration) remains largely unexplored, and relatively little is known about the mechanisms involved. However, it is likely that co-oxidations account for much of the “damage” normally attributed to lipid oxidation and provide footprints of lipid oxidation that are not detected in general assays of lipid oxidation.;In this research, primary experiments have compared the difference between proteins in baked and fried tortilla chips to distinguish thermal effects of processing from co-oxidation by lipids. Preliminary results showed little difference in protein solubility in fresh baked or fried chips, yet gel electrophoresis revealed significant lipid-mediated differences in disulfide cross-linking in fried chips even immediately after processing without incubations. Schiff base formation was present, but only at low levels, indicating that it is not a major source of cross-linking in early stages of oxidation. Cross-linking continued to develop even more extensively in fried chips during storage at 40 and 60 ºC, and included free radical in addition to disulfide cross-linking. Western blots revealed the presence of protein carbonyls, important co-oxidation products, in most protein fractions in tortilla chips and notably in zeins. Surprisingly, more carbonyls were observed in baked chips with lower lipid content.;To determine the connections between these protein changes and lipids, lipid oxidation is being followed in all systems by lipids extractability, free fatty acids, aldehydes and peroxides. |
