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The liver oil of the tecolote ray ( Rhinoptera steindechneri ) was characterized in terms of its lipid by-class composition and fatty acid profile, natural antioxidants content, oxidative resistance and physicochemical properties. The liver oil content was considered high and fluctuated between 57% and 67% of the liver weight (w/w). The carotenes and α -tocopherols levels varied from 2.9 to 17.4 mg/100 g of oil and 3.0 to 15.2 mg/100 g of oil, respectively. The oxidative resistance reported as the induction period varied between 2.1 and 4.7 h, showing a very stable oil due to its level of natural antioxidants. The triglycerides were the major lipid by-class in the oil (703–790 mg/oil g), followed in a smaller proportion by sterol esters, polar lipids and free sterols. The liver oil of tecolote ray proved to be an adequate source of the n-3 polyunsaturated fatty acids EPA and DHA, similar to the traditional codfish liver oil.

The omega-3 polyunsaturated fatty acids (PUFA) such as eicosapentaenoic (EPA) and docosahexaenoic (DHA), have been recognized for their important role in health. EPA has several beneficial effects regarding coronary heart disease, while DHA has been found to be important for the development of the brain and retina. The increase in the consumption of fish oil, a commercial source of PUFA, has made necessary the search for new fish species rich in PUFA that could be used as raw material for the fish oil production. The lipid, fatty acid composition and natural antioxidant contents (carotene, tocopherol) were analyzed for the liver oil of Dasyatis brevis (arenera) and Gymnura marmorata (mariposa), two ray species commercially captured in the Gulf of California. The liver oil yield 25–50% (w/w) for D. brevis and 38–56% for G. marmorata. The triglyceride fraction was the major lipid class (577–758 mg/g) for both species, with smaller proportions of sterol esters, free sterols, polar lipids and diacyl glyceryl ethers. D. brevis showed a greater carotene and tocopherols concentration (6.9 mg/100 g, 25.3 mg/100 g, respectively) than G. marmorata (1.8 mg/100 g, 2.8 mg/100 g, respectively). The content of saturated and monoenoic fatty acid was similar for both species, however, the liver oil of G. marmorata had twice as much DHA than D. brevis. The composite percentage composition of DHA plus EPA with respect to the total of fatty acids in liver oil was 18% for G. marmorata and 16% for D. brevis. The liver oil of G. marmorata and D. brevis represent a new source of omega-3 PUFA that can be used for human and animal nutrition.

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) derived from chemically or enzymatically hydrolyzed from sardine oil were concentrated by urea complexation. The enzymatic hydrolysis was effected in aqueous emulsion using five commercial lipases from Pseudomonas, three immobilized (PS-CI, PS-CII and PS-DI) and two soluble lipases (AK-20 and PS-30). EPA and DHA were determined by gas–liquid chromatography as methyl esters. Results showed that an immobilized lipase preparation (PS-CI) produced the highest degree of hydrolysis for EPA and DHA (81.5 and 72.3% from their initial content in the oil) after 24 h. After complexation of saturated and less unsaturated free fatty acids, the highest concentration of EPA (46.2%) and DHA (40.3%) was obtained using an ethanolic solution with 20% (w/w) urea and 12% (w/w) PS-CI hydrolyzed with a 78% yield. Combination of enzymatic or chemical hydrolysis with urea complexation is a promising method to obtain highly concentrated n-3 PUFA from sardine oil.