Marine oils : stabilization, structural characterization and omega-3 fatty acid concentration

Wanasundara, Udaya Nayanakantha (1996) Marine oils : stabilization, structural characterization and omega-3 fatty acid concentration. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Marine oils are obtained from the flesh of fatty fish, liver of lean fish and blubber of marine mammals. Seal blubber, a major product from the seal fishery, is abundantly available in Newfoundland and Labrador, but its characteristics have not been adequately defined. In this work, seal blubber oil (SBO) and cod liver oil (CLO) were extracted and refined under laboratory conditions. During each step of refining, oils were assessed for their oxidative stability by accelerated oxidation under Schaal oven conditions at 65°C over a 6 days period. Progression of oxidation was monitored by employing peroxide value (PV) determinations and 2-thiobarbituric acid reactive substances (TBARS) tests. Oxidative stability of processed oils after alkali-refining, degumming and deodorization steps was lower than that of crude oils, which is due in part to the removal of natural antioxidative compounds during refining. Oxidative stability of refined-bleached and deodorized (RBD) SBO and CLO was compared with that of commercially available menhaden oil (MHO); SBO exhibited a higher oxidative stability than CLO or MHO, perhaps due to its low content of polyunsaturated fatty acids (PUFA). -- Different procedures were examined for improving the oxidative stability of SBO and/or MHO. Particularly emphasis was placed on the use of natural antioxidants. Dechlorophyllized green tea extracts (DGTE, 100 to 1000 ppm), individual tea catechins [(-)epicatechin (EC), (-) epigallocatechin (EGC), (-)epigallocatechin gallate (EGCG), (-)epicatechin gallate (ECG)] and commercially-available flavonoids (apigenin, kaempferol, morin, myricetin, naringin, naringenin, quercetin, rutin and taxifolin) at 200 ppm levels were added to both test oils. Oxidative stability of treated oils was determined and compared to those treated with conventional antioxidants such as α-tocopherol at 500 ppm and BHA, BHT and TBHQ at 200 ppm levels. Progression of oxidation was monitored by employing weight gain, PV and TBARS tests. DGTE at 500 and 1000 ppm and individual tea catechins at 200 ppm exhibited better antioxidant activity than α-tocopherol (500 ppm), BHA and BHT (200 ppm) in these oils. Antioxidant activity of individual tea catechins in both oils was in the order of ECG > EGCG > EGC > EC; antioxidant activity of ECG was slightly better than that of TBHQ (200 ppm). Among flavonoids tested, myricetin, morin, quercetin, naringin and naringenin were more effective than α-tocopherol, BHA and BHT in retarding oxidation of both oils. Myricetin was the most effective flavonoid tested. Therefore, DGTE, isolated catechins and some flavonoids could be used as effective natural antioxidants for stabilization of highly unsaturated marine oils. -- In another set of studies, microencapsulation of SBO with different starch materials such as β-cyclodextrin, corn-syrup solids and maltodextrins was carried out in order to improve the oxidative stability of SBO. Encapsulated SBO was stored at room temperature for 49 days and its stability was monitored by measuring fatty acid composition, PV and TBARS. β-Cyclodextrin was the most effective encapsulating material used, as the resultant SBO retained 89% of its total PUFA. -- Stereospecific analysis was carried out to establish positional distributions of fatty acids in the triacylglycerols (TAG) of SBO and MHO. In SBO, eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) were located mainly in the sn-1 and sn-3 positions of the TAG molecules. In MHO, DPA and DHA were located mainly in the sn-2 position of the TAG, however, EPA was equally distributed amongst the sn-2 and sn-3 positions and was present only in small amounts in the sn-1 position. Therefore, EPA, DPA and DHA from SBO might be better assimilated in the body than those from MHO. -- In order to prepare ω3 fatty acid concentrates from SBO and/or MHO, three different approaches, namely low temperature crystallization, urea complexation and enzymatic hydrolysis were employed. Low temperature crystallization of free fatty acids of SBO gave a higher amount of total ω3 fatty acids in the non-crystalline fraction (concentrate) as compared to intact TAG. Approximately 58.3 and 66.7% of total ω3 fatty acids were obtained at -60 and -70°C when hexane was used as the solvent; corresponding recoveries were 39.0 and 24.8%. -- Urea complexation of saturated and/or monounsaturated fatty acids resulted in concentration of ω3-PUFA in the non-urea complexed fraction, thus allowing facile separation of ω3 fatty acids from marine oils. Process parameters such as urea-to-fatty acids ratio, crystallization temperature and crystallization time were optimized by response surface methodology (RSM) with a central composite rotatable design (CCRD) to obtain maximum amounts of ω3 fatty acids in the SBO concentrate. Total ω3 fatty acids of 88.2% (recovery of 24.5%) were obtained at a urea-to-fatty acid ratio of 4.5, a crystallization time of 24 h, and a crystallization temperature of -10°C. -- Preparation of ω3 fatty acid concentrates from SBO and MHO using enzymatic hydrolysis was carried out by first screening microbial lipases from Aspergillus niger; AN, Candida cylindracea; CC, Chromobacterium viscosum; CV, Geotrichum candidum, GC, Mucor miehei; MM, Pseudomonas spp.; PS, Rhizopus niveus: RN and Rhizopus oryzae; RO for their activities; CC-lipase was the most efficient enzyme examined. Optimization of hydrolysis parameters, namely enzyme concentration, reaction time and reaction temperature, gave a maximum of 54.3% total ω3 fatty acids from SBO (recovery of 30%) at an enzyme concentration of 308 U/g oil, a reaction time of 40 h, and a reaction temperature of 37°C. Similarly, a maximum of 54.5% total ω3 fatty acids was obtained from MHO (recovery of 43%) at an enzyme concentration of 340 U/g oil, a reaction time of 45 h, and a reaction temperature of 38°C. Therefore, low temperature crystallization, urea complexation and enzymatic hydrolysis by CC-lipase may be used to prepare ω3 fatty acid concentrates from marine oils.

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