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theses

Reformulation of foods to include nutritionally adequate levels of polyunsaturated fatty acids is seriously challenging existing lipid analysis methods. Current label requirements with detailed accountability for food composition create increase demands for analysis of total lipid composition that are accurate, sensitive, and fast. In addition, presence of unsaturated lipids dramatically increases oxidation, which is perceived as "rancid" off-odors and flavors by consumers, and food companies must be able to track this degradation to adequately stabilize foods and know when to pull products from shelves. Traditional methods of lipid analysis do not adequately meet these challenges. This dissertation research seeks to develop improved reversed phase high pressure liquid chromatography methods that simultaneously separate the lipid fractions most important in foods (free fatty acids, acylglycerols, and phospholipids) and quantitates each fraction while also analyzing lipid oxidation products. To achieve baseline separation of lipid lcasses, basic acetonitrile/water gradients were modified with hexane and isopropanol to solubilize long chain saturated fatty acids and triacylglycerols, and the aqueous phase was buffered to pH 6.8 to dissociate fatty acids and facilitate their separation from monoacylglycerols. Under these conditions, fractions separated according to equivalent carbon number. A cyano column (to establish column triple bond interactions with lipid double bonds ) in tandem with the reversed phase column did not increase separation of components within classes. Silver ion chromatography could not be applied because silver ions precipitate at neutral pH. Evaporative light scattering successfully detected low concentrations of all lipid fractions, including saturated components, but slopes of concentration curves varied with each lipid component. This allows quantitation but necessitates separate calibration curves for each component. A coulometric electrochemical cell with graphite electrode detected hydroperoxides but not aldehydes or epoxides. However, dinitrophenylhydrazones of aldehydes were detected by the coulometric cell; the response appears to be sensitive (micromolar) so may offer a superior alternative to optical detection of these products. Preliminary tests demonstrated superior detection of hydroperoxides with linear concentration response using an amperometric cell with glassy carbon electrode. Further studies with electrochemical detection of lipid oxidation products should focus on this method.

ETD_7297

Ph.D.

Includes bibliographical references

by Teng Peng

doi:10.7282/T3XS5XJN

ETD doctoral

The author owns the copyright to this work.