Epoxides have long been recognized as lipid oxidation products, and there is recent evidence that epoxides may be as or more important than hydroperoxides under many conditions. Nevertheless, epoxides are seldom analyzed when monitoring oxidative degradation, at least in part because there are few established analytical procedures. The goal of this thesis research, therefore, was to evaluate four available epoxide assays for accuracy, sensitivity, stoichiometry, reproducibility, and handling requirements, and from the results provide analytical protocols and practical guidelines for selection and application of assays for lipid epoxides. AOCS standard HBr titration of epoxides, nitrobenzylpyridine (NBP) reaction with colorimetric endpoint, diethyl dithiocarbamate (DETC) complexation with high pressure liquid chromatography (HPLC) separation and quantitation of adducts, and 1H nuclear magnetic resonance (NMR) analysis of epoxides were evaluated using epoxybutane, epoxyhexene, and epoxydecene as standards. The HBr assay is too insensitive (detects 0.0075-0.1M) for following lipid epoxides in foods and biological materials. In addition, the reaction must be run under inert atmosphere to prevent non-specific oxidation of the Br, and HBr degrades so rapidly that frequent restandardization is necessary. Nitrobenzylpyridine assay is more sensitive, detecting 0.5 mM epoxides. However, the NBP reaction response varied considerably with time and temperature of reaction and with epoxide structure (increased with epoxide chain length). Hence, a different standard must be used for each epoxide analyzed, and selection of an appropriate standard for epoxides of unknown structure is problematic. For the DETC assay, reaction response was linear from 1M to 1 mM for all three epoxide standards (R2 > 0.99) and oxidized methyl linoleate (R2 > 0.94), and increased with epoxide chain length. HPLC analysis of adducts allows differentiation and quantitation of individual epoxides, so can provide important information about oxidation chemistry as well as quantitation. NMR offers the advantage of direct analysis of oils and extracts, detects micromolar epoxides, and clearly distinguishes epoxides from other oxidation products in lipids. Response curves were linear with concentration of epoxide standards, oxidized corn oil, and oxidized methyl linoleate (R2> 0.98). The DETC-HPLC and NMR assays hold the greatest promise for routine analysis of epoxides in oxidized lipids.
Subject (authority = RUETD)
Topic
Food Science
Subject (authority = ETD-LCSH)
Topic
Epoxy compounds--Research
Subject (authority = ETD-LCSH)
Topic
Oxidation
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Rutgers University Electronic Theses and Dissertations
Rutgers University. Graduate School - New Brunswick
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License
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