| The Antarctic krill(Euphausia superb) has huge biomass and rich nutrition. In this paper, frozen krill was dried and smashed to produce krill meal, and krill oil was extracted from the krill meal by using multi-stage reverse extraction method. To improve the quality of the krill oil, the free fatty acids, unsaponification and insoluble impurity were removed. Meanwhile, phospholipids of the krill oil were enriched to produce different krill oil products with various contents of phospholipids. The present study provides technical support for industrialization of krill oil.In this study, food-grade n-hexane was used as extraction solvent. Under the condition of three-stage of extraction and solvent to krill meal ratio of 1:4(w/v), we got a stable oil recovery rate of more than 85%. In the oil, the phospholipid content accounted for over 60% of the total lipids, and the polyunsaturated fatty acids(PUFA) accounted for 25% of the total fatty acids. Among PUFAs, eicosapentaenoic acid(EPA) and docosahexaenoic acid(DHA) accounted for 12% and 6% of the total fatty acids. Therefore, it was concluded that the oil recovery rate, the lipid composition and the fatty acid composition of krill oil were stable during the multi-stage countercurrent extraction.In this study, sodium metasilicate, potassium bromide and low-temperature subsidence method were used to remove free fatty acids, unsaponifiable matter and insoluble impurities, respectively. Take acid value as an index, sodium silicate adding amount, mixing temperature, mixing time and mixing ratio of krill oil to hexane were optimized to get the suitable condition as below: the sodium silicate weight to krill oil weight ratio was 1:2, the mixing temperature was 40℃, the mixing time was 1h and the mixing ratio of krill oil with hexane was 1:3. Under this condition, the acid value of oil was 1.34mg/g. Take unsaponifiable matter content as an index, potassium bromide adding amount, mixing temperature and mixing time were optimized to get the suitable condition as below: the potassium bromide weight to krill oil weight ratio was 1:10, the mixing temperature was 40℃ and the mixing time was 2h. Under this condition, the unsaponifiable matter content was reduced to 0.65%. Take insoluble impurities content as an index, the precipitation time and the mixing ratio of krill oil to hexane were optimized to get the suitable condition as below: the precipitation time was 12 h under the temperature range from minus 4℃ to 4℃, and the mixing weigh ratio of krill oil to hexane was 1:3. Under this condition, the oil with the insoluble impurities content of 0.03% was obtained. Through the consecutively refining process described as above, the krill oil with high quality was obtained. The oil had acid valve of 1.34±0.19mg/g, peroxide value of 1.46±0.01mmol/kg, iodine value of 122.78±0.71g/100 g, unsaponifiable matter content of 0.65±0.05%, and insoluble impurities of 0.04±0.01%.To enrich phospholipids of krill oil, ethanol was used as solvent. Take mass fraction and phospholipid content of phospholipid layer as indexes, the krill oil to ethanol ratio(w/v), ethanol concentration, mixing temperature and mixing time were optimized to get the suitable condition as below: the krill oil to ethanol ratio(w/v) was 1:2, ethanol concentration was 95%, mixing temperature was 20℃ and mixing time was 20 min. Under this condition, the mass fraction of Antarctic krill phospholipids was 40%, and phospholipid accounted for 85.80±0.58% of the total lipids. By adjusting the mixing proportion of unphospholipids layer and phospholipids layer, we could get different krill oil products with various contents of phospholipids.The present study indicated that multi-stage reverse extraction method could improve the oil recovery rate, the consecutively refining method could improve the quality of krill oil, and the enrichment technology of phospholipids could enhance the kinds of krill oil products. These methods provide technical supports for industrialization of krill oil. |
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