Studies On The Storage Stability Of Phospholipids And The Forms Of Fluorine In Oil From Antarctic Krill(euphausia Superba)

The phospholipid-type omega-3 polyunsaturated fatty acids(PUFA) and astaxanthin give Antarctic krill(Euphausia superba) oil many bioactivities including anti-oxidation, anti-inflammation, anti-hyperlipidemic effect, anti-hyperglycemic effect and cardioprotective effect, etc, giving it great value of development and utilization. In the present study, we take krill as a researching object to investigate the storage stability of krill phospholipid and the forms of fluoride in krill oil.To study the stability of krill phospholipid, supercritical carbon dioxide(SC-CO2) coupled to absolute ethanol extraction were used to prepare krill phospholipids(KP). TLC-FID analysis indicated that phospholipids accounted for 92.81±0.22% of the total lipids. KP in colorless screw-top small teflon bottles were stored in various conditions including minus twenty degrees Celsius with oxygen, minus twenty degrees Celsius without oxygen, four degrees Celsius with oxygen, four degrees Celsius without oxyge, room temperature with oxygen, room temperature without oxygen, forty degrees Celsius with oxygen and light, forty degrees Celsius without oxygen and light, forty degrees Celsius with oxygen but without light, forty degrees Celsius without oxygen but with light. After storage for 1, 2, 3, 4, 6, 8, 10 weeks, KP were sampled to test the indexes including acid value(AV), free fatty acids(FFA), phospholipids, peroxide value(POV), TBARS value, fatty acid composition and astaxanthin.Results indicated that AV, FFA, phospholipids contents were unchanged for samples stored at-20 degrees Celsius, 4 degrees Celsius and room temperature. However, for samples stored at 40 degrees Celsius, from the sixth week, AV and FFA content began to increase, and phospholipids content were decreased at the same time. Light and oxygen could accelerate the variation. These results demonstrated that rancidity of KP took place at high temperature. Furthermore, for samples stored at all conditions, the indexes of POV, TBARS and fatty acid composition were relatively stable, indicating that oxidative rancidity was not occurred. However, astaxanthin content reduced gradually at 40 degrees Celsius, which showed that astaxanthin had effect of inhibiting KP oxidation.Results of storage stability indicated that KP should be stored at low temperature. When storage temperature changed dramatically, KP should be stored at condition without light and oxygen.Krill oils were extracted from hot-dried krill meal, freeze-dried whole krill meal and freeze-dried krill meat meal with hexane, and TISAB standard addition method was selected for measuring fluoride content of the krill oils. Results indicated that the fluoride content were 91.52±0.43mg/kg, 4.63±1.41mg/kg and 28.56±6.27mg/kg for the oils above. Meanwhile, protein content of the corresponding krill oils were 4.86±0.02%, 0.10±0.02% and 2.27±0.08%. According to the results described above, it was readily concluded that there were some positive correlation between fluoride content and protein content of krill oil.To further investigate the correlation between fluoride content and protein content, extracted liquid from hot-dried krill meal were stood for different time. Results indicated that fluoride content and protein content of krill oil were decreased with the extension of standing time. There was a linear positive correlation between fluoride content and protein content, indicating that fluoride in krill oil probably existed in residual protein.Next, krill oil without protein was prepared from hot drying krill meal with SC-CO2. Fluoride was not detected, which further proved that fluoride in krill oil existed in residual protein.Absorption method was used to remove fluoride from krill oil extracted form hot drying krill meal with hexane. Several absorbents including activated alumina particles, alumina powders, activated carbon, calcium oxide, activate clay, chitosan and calcium chloride were evaluated. Results indicated that activate clay had the highest removal rate of fluoride.Results of researches on the forms of fluoride in krill oil and fluoride removal experiment indicated that fluoride in krill oil existed in residual protein, the fluoride can be removed through absorption with activate clay.