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Effect of oil blending and use of natural antioxidants on the chemical composition and thermal stability of oils rich in polyunsaturated fatty acids

University of British Columbia

The procedure of blending ω-3 polyunsaturated fatty acids (PUFAs) oils with a medium chain, saturated butter oil was initiated for the purpose of minimizing the loss of ω-3 fatty acids to oxidation reaction. The two sources of ω-3 PUFA used were flaxseed oil (rich in ω-3 linolenic acid) and fish oil (rich in very long chain ω-3, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). A common consequence of the dilution of PUFAs by saturated fatty acids present in butter oil was a reduced peroxide value (PV), lower conjugated diene hydroperoxides (CDH) and thiobarbituric acid reactive substances (TBARS) following accelerated oxidation induced by thermal treatment at both 150°C and 180°C, for periods of 8, 16, and 24 h, respectively. The P/S (polyunsaturated to saturated fatty acid) and ω3/ω6 (ω3 to ω6 fatty acid) ratios were both shown to represent predictive indicators of PUFA depletion when fitted to a quadratic model describing the influence of the blend proportions derived from fish oil and butter oil. No optimum could be reached for a blending composition to maximize these indicator ratios of PUFA retention. Moreover, it was determined that both EPA (C20:5ω3) and DHA (C22:6ω3) in fish oil were in fact, more susceptible to thermal oxidation after blending with butter oil. Blending of flaxseed oil with butter oil improved resistance to thermal oxidation as indexed by PV, CDH, and TBARS throughout 8, 16 and 24 h heating periods. A regression, quadratic model effectively optimized the blend of butter oil with flaxseed oil (i.e. 76% flaxseed oil; 24% butter oil) in respect to maximizing the ω3/ω6 ratio. The procedure of cholesterol resulted in a greater stability of the flaxseed oil, as evidenced by significant reductions in TBARS and greater retention of ω-3 and ω-6 PUFAs (P<0.01). Cholesterol oxidation products (COPs) were identified and shown to vary in production as a result of absolute temperature of heating, time of heating and source of oil used in the heating experiment. The combination of adding natural antioxidants, such as rosemary, sage extracts and citric acid was also investigated as a different blending strategy to prevent lipid oxidation in these ω-3 rich oil sources. A quadratic model described the optimization of different proportions of the three antioxidants resulting in a combination of 0.067% rosemary extract, 0.067% sage extract and 0.05% citric acid for a maximal stability of the oil (as evidenced by the lowest formation of CDH). The addition of an optimal mixture of 0.1% rosemary extract, 0.1% rosemary extract with 0.05% citric acid was found to also facilitate a greater retention of linoleic acid and a-linolenic acid in flaxseed oil.

Thesis/Dissertation

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2009-07-30

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http://hdl.handle.net/2429/11520

Food Science

University of British Columbia

UBCV

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