Study On The Aqueous Enzymatic Extraction Of Freshwater Fish Oil And Analysis Of Its Volatile Compounds

China is the largest freshwater fish producer, more than60%of world production, andstill in the stage of sustained growth. About10%of fish offal in freshwater fish, and thevisceral fat is very important resource, but the smell of the fat from visceral affect consumeracceptance. Therefore, oil extraction from freshwater fish offal use protease,Removal of smellof fish oil and the oxidation of fish oil has been analysed and discussed in order to providetechnical guidance for the utilization of scraps from freshwater fish.First,compared the quality of fih oil were obtained using different methods, found thatthe fish oil use enzymatic extraction has higher PUFA content than another traditional way.The PUFA contents of fish oil from five freshwater fish offal used two different methods were25.73~32.65%and24.74~31.70%, and the rate of enzymatic extraction is much higher thantraditional alkaline hydrolysis.Secondly, determined the best route of The process of aqueous enzymatic extraction offish oil: solid to liquid1:1, reaction time2h, pH7.96, the dosage of trypsin enzyme6170U/g, the hydrolysis temperature46.17oC. Under this condition, the extraction rate of oil was asmuch as93.80%. The quality of the unrefined fish oil reached the second grade of SC/T3502-2006,and the first grade or fortified grade can be achieved through refining process.Then, detected and analysised the volatile components in fish oil use GC-MS, a total of30kinds of aldehydes, nine kinds of ketones,22kinds of phenols, alcohols, nine kinds ofacids,36kinds of hydrocarbons and12kinds of esters, while there are still some heterocyclicoxides such as furan. Which accounted for the highest proportion of volatile substances in fishoil were aldehydes, accounting for45.26%of the relative content. Which accounted forrelative high proportion of the total content of volatile components were: Pentanal(3.71%),(E)-2-Pentenal(1.66%), Hexanal(2.94%),(Z)-4-Heptenal(3.44%),(E,E)-2,4-Heptadienal(4.69%), Phenylacetaldehyde(5.05%),(E)-2-octenal(2.16%), Nonanal(1.87%),(E,E)-2,4-decadienal(1.63%),(E,Z,Z)-2,4,7-decatrienal(2.40%),2-Undecenal(1.51%) etc. The vola-tile components of each refining step were tested and found that bleaching and moleculardistillation of fish oil can effectively removing volatile substances. Four different adsorbentswere compared and found that activated carbon has the best deodorization effect. Whileoptimizing the molecular distillation deodorization conditions, choose190oC deodorizingbest.Finally, storage tests of fish oil after four different adsorbents processed were tested,different adsorbent effects stability of fish oil differently during storage, especially forpophase of storage, which was treated with activated carbon is more susceptible to oxidationin the pophase of storage. During storage,4-ethenyl-clohexanone,5-methyl-4-hexen-3-one,Pentanal, Hexanal, Heptaldehyde,(E)-2-Heptenal,(E,E)-2,4-Heptadienal,(E)-2-octen-1-al-dehyde,(E,E)-2,4-Octadienal,3-Heptylacrolein,2-Undecenal,(E)-2-pentenol, Mushroomalcohol increased with prolonged storage time increases. The most stable growth significantlywere Pentanal, Hexanal, Heptaldehyde,(E,E)-2,4-Heptadienal,(E)-2-pentenol. Among thesecompound, the growth rate of oxidation products of linoleic acid and other polyunsaturated fatty acid is significantly faster than oleic. Adding antioxidants can significantly improve theoxidative stability of fish oil, TBHQ has the best antioxidant effect among three antioxidants,and tea polyphenols is similar to the effect of VE. Different antioxidants will make thecomposition of the volatile components of fish oil changes, fish oil added TBHQ and teapolyphenols have less content of flavor volatiles than which added VEor nothing, the mostobvious is (E,E)-2,4-Heptadienal,(E,Z,Z)-2,4,7-decatrienal,(E)-2-pentenol.