Study On The Green Extraction Technology Of Oils From Antarctic Krill(Euphausia Superba)

Antarctic krill(Euphausia superba)is a type of marine organism with huge biomass and rich nutrition.In this thesis,krill oil was extracted from Antarctic krill by using supercritical CO2 extraction and enzyme-assisted aqueous extraction method.Furthermore,the lipid composition and fatty acid composition of krill oil extracted were analyzed,which provided a basis for industrialization exploitation of the Antarctic krill oil.In krill oil extraction by supercritical CO2 extraction,the extraction temperature,extraction pressure and extraction time were optimized by using oil recovery as an index.The optimal conditions were determined as follow:the extraction temperature is 40?,the extraction pressure is 25 MPa,and the extraction time is 90 min.Under this condition,the oil recovery rate is 55.57%.Taking acid value of the extracted oil as an index,the optimal conditions were determined as follow:the extraction temperature is 35 ?,the extraction pressure is 30 MPa,and the extraction time is 90 min.Under such conditions,the acid value of the extracted oil is 5.24mg/g,which is much lower than that of soxhlet extraction(14.71mg/g).Krill oil extracted by supercritical CO2 extraction composed mainly of triglyceride,which accounted for over 85%of the total lipid.The krill oil also contained a small amount of diglyceride,cholesterol and free fatty acids,but did not contain phospholipid.Krill oil extracted under optimal conditions contained 31.08%of PUFA,35.69%of MUFA and 33.24%of SFA,respectively.Compared with the oils extracted using n-hexane and ethanol as the solvents,the oil extracted by supercritical CO2 extraction contained less PUFA but more SFA.When extracting krill oil by enzyme-assisted aqueous method,three schemes were designed.Scheme 1 included an enzymatic hydrolytic process and a directly centrifugal process.Scheme 2 added an enzyme destruction process after enzymatic hydrolytic process based on scheme 1.Scheme 3 added a thermal treatment step for raw material based on the scheme 2.After centrifugation,the hydrolysates formed four layers from top to bottom in turn as free oil + emulsion layer 1,water layer,emulsion layer 2,and residue layer.For scheme 1,oil extraction rate for the free oil + emulsion layer 1 is the highest(1.15%).For scheme 2,oil extraction rate for the emulsion layer 2 is the highest(2.04%).For scheme 3,oil extraction rate for the emulsion layer 2 is the highest(1.67%).For dry matter of the four layers,the oil content of emulsion layer 2 was highest,which reached 51.27%when adopting scheme 2.Meanwhile,the oil content of water layer is lowest,which was just 8.36%when adopting scheme 3.Fatty acids compositions and lipid compositions have a certain correlation:the more phospholipids content,the more PUFA content.PFUA,EPA and DHA content of dry matter from water layer extract by scheme 1 are 41.57%,22.03%and 11.45%,respectively.The present study indicated that the supercritical CO2 method without entrainer failed to extract phospholipids from krill.However,the method may effectively get rid of all other lipids except for phospholipid of raw materials,which lay a foundation of extracting krill phospholipids with high purity.Enzyme-assisted aqueous extraction method failed to extract krill oil with high purity,but can remove shrimp shell,and enrich oil.