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theses

Tropical fats such as coconut oil contain medium chain fatty acids which activate lipases, converting fats directly into energy rather than storage in adipose tissue. Implications that these fats may be helpful in reducing obesity and related diseases, and also replace trans fats in foods, have led to interest in developing "healthy" coconut oil-based products for use in table spreads, cooking, and baking applications. This study evaluated effects of water quality, antioxidants, and oil components on thermal and oxidative stability of margarine-type blends (coconut oil, palm shortening, and high oleic sunflower oil with/without polyunsaturated canola and flax seed oils) developed for baking and sautéing applications. Thermal stability was determined by heating blends in an OxipresTM oxygen bomb at 80, 100, 120, and 150C to simulate baking, sautéing, and frying applications, respectively. Refrigerated shelf life was determined in blends stored in glass jars sealed under argon for up to one year. Samples were analyzed periodically for lipid oxidation by conjugated dienes and hydroperoxides (chemical analyses), carbonyls (dinitrophenylhydrazine reaction with high pressure liquid chromatography detection and quantitation), and formation of volatile degradation products (gas chromatography). Thermal and shelf stability varied with unsaturated fatty acid composition of the blends; products were detected from all unsaturated fatty acids present. Handling during preparation and storage, as well as quality of the water used in the blend, was also important in directing stability. No blend tested maintained acceptable peroxide levels when heated at 150C. Blends with higher levels of canola and flax seed oil degraded unacceptably at 100C. Peroxide values did not accurately reflect degradation of tropical fat-based blends. Mixed tocopherols added at levels from 200 to 1000 ppm paradoxically increased peroxide and aldehyde levels during heating and storage. Maximum peroxides were <20 and only low levels of aldehydes were present, yet strong off-odors and flavors were present. Butanal, in particular, was produced in unusually high levels. These results can be explained by alternate oxidation pathways including peroxyl radical addition to double bonds and epoxide formation exceeding hydroperoxide formation and scission. Tocopherols stabilized hydroperoxides by hydrogen bonding and shifted oxidation back to standard pathways.

ETD_6988

M.S.

Includes bibliographical references

by Emily Nering

doi:10.7282/T39G5PV3

ETD graduate

The author owns the copyright to this work.