Oxidative stability of stripped and non-stripped borage and evening primrose oils and their oil-in-water emulsions

Khan, Muhammad Ahmad (1999) Oxidative stability of stripped and non-stripped borage and evening primrose oils and their oil-in-water emulsions. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (18MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Borage and evening primrose oils have been used for the treatment of a wide range of nutritional and clinical disorders. However, very little information is available about the oxidative stability of these nutritional oils and virtually nothing is known regarding their minor components-stripped counterparts. Therefore, this research was initiated to evaluate the oxidative stability of borage and evening primrose oils and their oil-in-water emulsions as well as their minor component stripped counterparts in the dark at 60 C and under fluorescent light at 27 C. Several analytical methods were used to assess the oxidative stability of oil and emulsion systems. The correlations between peroxide values (PV) and conjugated dienes (CD) as well as thiobarbituric acid reactive substances (TBARS) and hexanal content for all samples have been examined. Moreover, the effectiveness of natural and synthetic antioxidants as well as phospholipids to inhibit the oxidation of stripped borage and evening primrose oils was evaluated in the dark at 60 C. -- The results indicate that minor components play a major role in the oxidative stability of borage and evening primrose oils and their emulsions in water in the dark as well as in the light. Moreover, the endogenous antioxidants in the emulsion system may or may not behave according to the polar paradox theory. Correlations have been observed (r>0.514, P<0.05, n=15) between PV and CD as well as TBARS and hexanal content for most oils and emulsion systems stored in the dark or under fluorescent light. -- Delta-tocopherol was more effective as an antioxidant than alpha-tocopherol in stripped borage and evening primrose oils. Meanwhile, the most effective natural antioxidant was Tenox GT-2 (which is a mixture of α-, γ-, and δ-tocopherols) at 500 ppm while TBHQ at 200 ppm was the most effective synthetic antioxidant in both oils. Moreover, the oxidative stability of stripped borage and evening primrose oils was increased by a mixture of tocopherols and phospholipids. These results may be used to: (I) provide simple and reliable analytical methods to follow the oxidation of stripped and non-stripped borage and evening primrose oils, (2) enhance our understanding of the parameters involved in the oxidation of nutritional and medicinal oils and their emulsions in water, (3) design proper refining processes to retain optimum amounts of minor components and (4) improve the oxidative stability of stripped borage and evening primrose oils through natural and synthetic antioxidants.

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