Study On The Extraction Process And Properties Analysis Of Fish Oils From The Abdomen Of Silver Carp

As one of the most important industries of our country, the freshwater fisheries are generating lots of by-products with the increasing annual output and processing proportion. So the developments of freshwater fish by-products are of great importance in adding attachedvalue and reducing resource depletion. The abdomen part of freshwater fish is rich in fatty, but makes little functional contribution to surimi products, and even has a negative impact. Therefore, it is expected to improve the efficiency in the processing of fresh water and extend the raw materials sources of fish oils if the abdomen part can be exploited. Thus, the method of extracting oils from freshwater fish’s abdomen and the refining process have been researched in this study. And the quality of the fish oils was evaluated and improved in order to provide technical guide for development of freshwater by-products and the extraction and preservation of freshwater fish oils.Firstly, the basic ingredients and fatty acid composition of abdominal tissue from silver carp, bighead carp and grass carp were analyzed. The results showed that the fat content of abdomen from three samples was higher than fish body and other by-products, especially the 22.40% content of silver carp. The ω-3/ω-6 value of silver carp, bighead carp and grass carp were 3.17, 2.21 and 0.21, and the two former’s values were close to marine fish, which indicated a high nutritional value. And the silver carp contained the highest EPA and DHA content, respectively 6.33% and 5.09%. So the silver carp was chosen as experimental materials because of its higher nutritional value.Secondly, the optimal conditions of enzymatic hydrolysis process and the press method were determined according to the single factor and response surface optimization experiments, the optimal process of enzymatic hydrolysis was ultimately determined as follows: alkaline protease enzyme was the most effective for this materials, and the highest 64.32% extraction rate of fish oil was obtained at the conditions of 1.0︰1 liquid-to-solid ratio, 54℃ hydrolysis temperature, 8176 U/g enzyme dosage, and 8.6 pH value for 3 h. Then the cooking temperature, cooking time and press pressure of press method were examined based on the extraction rate and physicochemical properties, the results showed that the extraction reached the highest 39.77% at 80℃ for 30 min with the 8.3 MPa press pressure.The results also showed that the fish oil obtained by enzymatic hydrolysis displayed better quality with lowest peroxide value and acid value, respectively 5.48 mmol/kg and 3.56 mg/g, whose ω-3/ω-6 was 2.89 and indexes reached the first grade of crude fish oil standard. The ω-3/ω-6 value of fish oil extracted by press method was 4.17, and the oil performed well in physical properties with less impurities and higher nutritional value. Because of the highest impurity content, the oil extracted by solvent method showed the poorest quality. The fishy smell of oils extracted by enzymatic hydrolysis, press and solvent method was light, very slight and heavy, with 25, 21 and 41 kinds of volatiles detected. The main volatile substances contained saturated alkanes, alkenes, alcohols and phenols, and 1-octene-3-ol and E,E-2,4-heptadienal made greater contributions for the smell.The crude fish oils were refined to improve the quality by degumming, deacidification, deodorization and decolorization process. The peroxide value and acid value of oils extracted by enzyme and press method decreased apparently, respectively 2.68 mmol/kg, 1.12 mg/g and 2.56 mmol/kg, 1.07 mg/g, complied with the second grade of refined fish oil standard, refining recoveries were 73.11% and 78.32%, and the final extraction rates were 47.02% and 31.15%. Therefore, from the perspective of practical operation process and the oil quality, the press method was more suitable for extracting oil from freshwater fish’s abdomen. Finally, the rosemary extract and vitamin E were added into fish oils to study the antioxidant capacity. The results showed that rosemary extract demonstrated better antioxidant effect at a lower concentration, and could significantly enhance the oxidative stability of fish oil.