Study On Extraction Technology Of Antarctic Krill

Antarctic krill is a resource with a large quantity and is rich in proteins with highnutritional value. However, due to some technology bottlenecks, so far the Antarctickrill protein resources have not been fully utilized. Hence, in the thesis, theNitrogen-to-protein Conversion Factor (NPCF) of aquatic protein was determinated,isoelectric solubilization/precipatation (ISP) system was used to extract Antarctickrill protein, a new method of removing fluoride was established and multi-stagecountercurrent technology was applied into protein extracting and fluoride removing.The results are summed up as follows:1. A novel theoretical calculation model of NPCF has been put forward.According to this model, NPCF values of common proteins such as soybean, dairy,and so on were calculated. Furthermore, using the recommended values of NPCF inChinese National Standard (GB50095-2010), the range of ratio between Glu+Aspand Gln+Asn (AO/AE) have been determined as1.370.85. Then the NPCF values ofAntarctic krill (Euphausia superba), Yellowfin Tuna (Thunnus bacares) and Chineseshrimp (Fenneropenaeus chinensis) were calculated by above model and the aquaticprotein NPCF was determined as5.680.10.2. ISP process was applied to Antarctic krill protein extraction. Solubility ofAntarctic krill proteins and fluoride contents in the solutions were studied betweenpH1.00-13.75. The results showed that solubility of Antarctic krill proteins reached aminimum at pH4.5and a maximum at pH13.5, and protein extraction conditionswere improved in accordance with the results. The protein recovery yield increased to63.50%. As pH changes, the concentration of dissolved fluoride remained relativelyunchanged (16.78-20.50mg/L), within pH2.00-13.50. Therefore, water washingmethod was applied to remove fluoride. After4-times washing, fluoride could bereduced by98.14±0.01%from krill with about5.14±0.21%protein loss. The pIdistribution of the krill proteins dissolved at several pH were investigated byisoelectric focusing (IEF). The result showed that the extreme condition of pH13.50 has little impact on pI of prteins. At room temperature, the autolyzed rate of Antarctickrill protein is less than1.00%in6h.3. Multi-stage countercurrent system was used to optimize protein extracting andfluoride removing. The protein dissolving limit was measured at pH13.50and thedissolving law during this process was analyzed by SDS-PAGE. After investigated themultiple extracting process, the multi-stage countercurrent system was used tooptimize protein extracting and fluoride removing and protein extraction conditionswere analyzed by single-factor experiment. The results showed that the proteindissolving limit reached up to36.96±0.82mg/mL at pH13.50. From SDS-PAGE，theproteins dissolving of Antarctic krill mainly happened in three different molecularweight areas (18.4,35.0-45.0and116.0kDa) and proteins in different areas displayedvarious dissolving characteristic. After using multi-stage countercurrent system,protein recovery yield of Antarctic krill could increase24.06%at the same waterconsumption and fluoride removal rate could reach98.58±0.01%using only1/4ofthe water.