Background. Natural antioxidants become increasingly important in fish processing and particularly in the preservation phase of fish raw materials. Some of them can protect lipids, containing essential unsaturated fatty acids. The aim of the present study was to determine antioxidant properties of aqueous extracts of rosemary and sage, compared with the activity of BHA (butylated hydroxyanisole) and Endox in lipids of fresh Baltic fishes (herring, sprat, flounder) and those subjected to frozen storage at -25°C for 6 months. Materials and Methods. Antioxidant activity of the additives was determined based on β-carotene changes in fish lipids after 10, 20, 40, and 60 min of heating at 50°C. Results. The plant-origin extracts and the synthetic antioxidants used, inhibited most extensively β-carotene changes in the lipids of non-frozen herring. They were the least effective in non-frozen sprat lipids. The frozen storage lowered the antioxidant action of the additives in relation to β-carotene in lipids of herring and flounder, whereas in sprat lipids the antioxidants used, continued their protective action for β-carotene, during heating. Elongation of the heating time from 10 to 60 min increased the β-carotene losses and their pace followed the logarithmic scale. The activity of the antioxidants in fish lipids decreased along with the increase of polyunsaturated fatty acids (C20 : 5, C22 : 5, and C22 : 6) contents Conclusion. The antioxidant properties of plant-origin additives and synthetic antioxidants decreased along with the increased content on unsaturated fatty acids of fish lipids. Six-month-long frozen storage of the fish raw materials resulted in a decrease of the protective properties of the additives used, in relation to the lipids of Baltic herring and flounder. The best protective properties for lipids of flounder and sprat exhibited Endox, while aqueous extract of rosemary was the most effective in relation to sprat lipids.
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