CHARACTERISTICS OF FISH OILS IN TROPICAL FOOD FISHES

Abstract

Of the 41 species of fish and shellfish studied, 34 (83%) were lean fish (<5% total lipid), with the 6 most abundant fatty acids being palmitic, stearic, oleic, docosahexaenoic, palmitoleic and myristic. Arachidonic acid was also present in substantial amounts. The majority had higher docosahexaenoic acid (DHA) as compared to eicosapentaenoic acid (EPA). As the fishes were very lean, only two (longtail shad and golden toothless trevally) species had more than 1g EPA/100g skin-on fillet and head tissues respectively, and five species (longtail tuna, longnose trevally, wolfherring, barred Spanish mackerel and golden toothless trevally) with more than 1g DHA/100g head tissue. As such they may not be that useful for commercial extraction in fish oil capsule preparations. The freshwater catfishes were rich in ?-6 fatty acid, especially linoleic acid, and extremely poor in ?-3 fatty acids, when compared against the marine teleost. The spot-tail shark was generally a very lean fish in terms of fatty acid composition except in the gut. In general the total lipid, triglyceride (TG) and cholesterol (CH) levels were higher in the head, roe and gut tissues in all species when compared to th muscle tissue. However, in the prawns and squid samples, the cholesterol level were equally high in the head and muscle tissue. Though the squid had fairl high cholesterol and triglyceride levels, they were also rich in DHA. The India anchovy was also a rich source of DHA. The crab species however, had highe levels of EPA than DHA. Iced storage studies showed that lipid hydrolysis and oxidation were no critical spoilage parameters in iced stored Indian mackerel. Frozen storage of Spanish mackerel showed that the shelf life at-10°C was 4 months while those stored at -20°C was still of acceptable quality after 6 months.

In the study on the effect of diet on fish oil composition, the results showed that though feeding oil-enriched formulated feed did not significantly affect the total lipid and ?-6 fatty acid content of the various tissues when compared to trawl by-catch sea bass, ii did significantly increase the total saturated, monoenoic, polyenoic and total unsaturated fatty acids as well as the ?-3 to ?-6 ratio. Thus the oil-enriched formulated feed was observed to enhance the ?-3 fatty acids in the various tissues of the farmed sea bass.

In general, microwave heating, baking and steaming did not significantly change the fish oil characteristic of barred Spanish mackerel when compared to raw sample. The only significant changes were observed in the fried samples. However, the effect was due primarily to the absorption of sunflower oil into the fried fish tissues, resulting in an increase in the proportion of ?-6 and polyenoic acids because of the very high C18:2 fatty acids in sunflower oil. However, all modes of heating did significantly reduce the ?3/?6 ratios in the barred Spanish mackerel when compared with the raw samples.