| Channel catfish(Ictalurus punctatus), originally found in North America, is one of the most commercially import freshwater fish species well-accepted by consumers all over the world. In recent years, Channel catfish has been widely cultured in China. The statistic data shows that in 2007, the estimated yield of channel catfish was at least 140,000 tonnes in China. Being delicious in taste and lack of inter-muscular bones, the most of the channel catfish processed in China is sold as fresh or frozen fillets. The viscera of channel catfish are one of the primary by-products of filleting processing. The amount of protein content and lipid in the viscera was up to 8.58% and 28.14%, respectively. Thus it can be seen that the viscera are not only fish oil resource but also protein resource. This paper was mainly concerned with the extraction method of fish oil from the viscera of channel catfish, then the crude fish oil was refined, at last, effects of antioxidant on the stablility of the refined fish oil were systematically studied.Crude fish oil was extracted in this study from the viscera of channel catfish by a modified potassium hydroxide hydrolysis method and aqueous enzymatic extraction method, which was evaluated with the index of extraction ratio of fish oil. The two different extraction methods were compared and analysed. Based on the technology of Potassium-method, the results showed that the optimal extraction conditions were that:initial hydrolysis pH 7.0, ratio of viscera to water 1:1.5, hydrolysis temperature 65℃, hydrolysis time 35 min, the amount of potassium chloride 4%, the salt out time 10 min. The extraction ratio of fish oil was up to 82.09% under optimal conditions. The optimum parameters of aqueous enzymatic extraction method were as follows:initial hydrolysis pH 7.5, ratio of viscera to water 1:1, amount of papain 3500 U/g, hydrolysis time 0.5 h, hydrolysis temperature 55℃. Under these conditions, the extraction ratio of fish oil was as much as 80.94%. The extraction ratios of crude fish oil, which was made by the optimum conditions of two methods, were almost the same. According to the physicochemical indices of rude fish oil, it can be believed that the quality of crude fish oil gained by aqueous enzymatic extraction method were better than that of crude fish oil gained by Potassium-method. Therefore, aqueous enzymatic extraction method was chosen as ultimate fish oil extraction process.The crude fish oil was refined by degumming, neutralizing, bleaching and deodorizing. The refined fish oil was yellowish and transparent with very light fishlike smell. The physicochemical indices of crude fish oil were determined, which reached to the fist-grade of SC/T 3502-2000 criterion of aquatic industry of refined fish oil except the iodine value. The compositions and contents of fatty acid in the refined fish oil were analyzed by gas chromatography-mass spectrometry. The results showed that there were mainly 19 kings of fatty acid including C14-C22 in refined fish oil, in which there were 6 kinds of saturated fatty acids,5 kinds of single unsaturated fatty acids, and 8 kinds of polyunsaturated fatty acids. The content of saturated fatty acids, single unsaturated fatty acids and polyunsaturated fatty acids were 20.37%,65.20%, and 13.66% respectively.By using the peroxide value as an index, the antioxidant effect of sodium D-isoascorbate,tea polyphenols and rosemary on refined fish oil was studied by Schaal oven-storage test. The results demonstrated that, the capability order of antioxidation is:tea polyphenols> rosemary>D-isoascorbate when the antioxidants amount added accounting for 0.02% of the oil. The antioxidant effect of tea polyphenols increased with the enhancement of concentration. No matter whether citric acid or vitamin C added as the accessory, the antioxidant effect of tea polyphenols was improved, and Vitamin C exhibited more remarkable synergistic antioxidation effect than citric acid.
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