Production of structured lipids via enzymatic interesterification of gamma-linolenic acid (GLA) and marine oils

Spurvey, Sharon A. (2002) Production of structured lipids via enzymatic interesterification of gamma-linolenic acid (GLA) and marine oils. Masters thesis, Memorial University of Newfoundland.

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Abstract

The importance of polyunsaturated fatty acids (PUFA) in human nutrition and disease prevention has long been recognised. Both ω3 and ω6 PUFA serve as precursors of eicosanoids, which are involved in many important biochemical processes in the human body. -- Omega-3 fatty acids, which are present in marine oils, play an important role in the prevention and treatment of coronary heart disease, hypertension, arthritis, and other inflammatory and autoimmune disorders as well as cancer. Gamma-linolenic acid (GLA), an ω6 fatty acid, is present in oils from borage and evening primrose seeds at 17-25% and 8- 10%, respectively. GLA has been reported to be important for the prevention and/or treatment of skin diseases, pre-rnenstraal syndrome, diabetes, inflammatory and autoimmune disorders, and cancer. -- Urea complexation of borage oil resulted in the concentration of gamma-linolenic acid (GLA) in the non-urea complexed fraction thus allowing easy separation of GLA from the hydrolysed borage oil. The process parameters such as the mole ratio of urea-to-fatty acid, reaction temperature and reaction time were optimised by response surface methodology (RSM) using a 3-factor-3-level face-centred cube design to achieve the maximum amount of GLA in the borage oil concentrate. The optimum conditions for production of GLA concentrate were: urea-to-fatty acid ratio of 3.7, reaction temperature of -7°C and reaction time of 16 h, which yielded a 91% GLA concentrate. -- The GLA was subsequently enzymatically reacted with seal blubber oil and menhaden oil to produce a structured lipid. The process variables studied for the lipase-esterified reaction were the concentration of enzyme (100-700 units/g of oil), reaction temperature (30-60°C), reaction time (0-48h) and the mole ratio of GLA to triacylglycerols (TAG) (1:1-5:1). Two lipases chosen for the interesterification reaction were from Pseudomonas sp. and Mucor miehei. The lipase from Pseudomonas sp. was chosen over that from Mucor miehei to catalyse the interesterification reaction due to higher incorporation of GLA. For the interesterification reaction, the best conditions were 3:1 mole ratio of GLA to TAG, reaction temperature of 40 °C, reaction time of 24 h and an enzyme concentration of 500 units/g of oil. Under these conditions, incorporation of GLA was 37.1% for seal blubber oil (SBO) and 39.6% for menhaden oil (MO). The resultant oils containing both ω3 and ω6 fatty acids are considered important for clinical as well as nutritional purposes. -- Stereospecific analysis was carried out to establish the positional distribution of fatty acids in the triacylglycerols (TAG) of the modified seal blubber oil (MSBO) and modified menhaden oil (MMO). In MSBO, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA) were located mainly in the sn-l and sn-3 positions of the TAG molecules. In MMO, EPA, DHA and DPA were equally distributed amongst the sn-l, sn-2 and sn-3 positions of the TAG. GLA was also present in all positions of the TAG of MMO and MSBO. This indicates that lipase from Pseudomonas sp. (PS-30) was able to involve the middle position of the TAG in the acidolysis process. Thus, structured lipids containing EPA, DHA, DPA and GLA were successfully produced; consumption of these products is expected to render health benefits. The structured lipids (MSBO and MMO) produced were assessed for their autoxidative and photooxidative stability toward accelerated oxidation under Schaal oven conditions at 60°C, or storage at room temperature under fluorescent lighting. Conjugated diene (CD), 2-thiobarbituric acid reactive substances (TB ARS) and nuclear magnetic resonance (NMR) determinations were employed to monitor progression of the oxidation of the oils. During autoxidation, the modified oils were least stable due to their high content of polyunsaturated fatty acids (PUFA) and loss of natural antioxidants during the acidolysis process. In the case of photooxidation, both the modified and unmodified seal blubber oils (SBO and MSBO) were more stable than their MO counterparts. The presence of highly polyunsaturated fatty acids (PUFA) in the latter oils as well as photosensitizers, such as chlorophyll in MO, might be responsible for this observation.

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