Fish and fish oils are the richest sources of ω-3 fatty acids. However, they are susceptible to lipid peroxidation due to their high degree of unsaturation. In the present study, the level of thiobarbituric acid reactive material in various fish oils available in the market with and without added Vitamin E was determined. The peroxide levels in fish oil heated to food frying temperature of 180 0 C and the effect of addition of vitamin E has also been studied. The results indicate that the peroxide levels in almost all the products available in the market were abnormally high irrespective of their Vitamin E content. This might be due to the inefficient methods used for processing and storage of fish oils. Addition of vitamin E was found to have a significant effect in lowering the rate of peroxidation of fish oil during thermal stress, showing that association of antioxidants with ω-3 fatty acids lowers the rate of lipid peroxidation.
The levels of cytotoxic aldehydic products in different culinary oils, with or without thermal stress, (routine domestic or commercial frying) were determined by thiobarbituric acid method. The results showed that (i) thiobarbituric acid reactivity was much higher in edible oils rich in polyunsaturated fatty acids than those rich in saturated fatty acids or monounsaturated fatty acids, even without thermal stress, (ii) the lipid peroxide levels were in proportion to the duration of thermal stress, (iii) nature of the container used (steel, iron or teflon-coated) had no significant effect on the extent of lipid peroxidation under identical conditions of thermal stress and (iv) thermally stressed oils collected from hotels and roadside caterers contained higher levels of cytotoxic aldehydic products, when compared to oils thermally stressed under domestic frying conditions. These results suggest that dietary ingestion of thermally or autoxidatively stressed polyunsaturated fatty acid rich culinary oils is more harmful compared with those similarly treated oils rich in saturated fatty acids and monounsaturated fatty acids.
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