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Study of Defluorination Techniques from Antarctic Krill Hydrolysate

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Tutor: XueChangHu
School: Ocean University of China
Course: Aquatic Products Processing and Storage Engineering
Keywords: Antarctic krill,hydrolysate,defluorination,nanofiltration,electrodialysis,chemic
CLC: TS254.4
Type: Master's thesis
Year:  2011
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The fluoride content of Antarctic krill (Euphausia superba) is 1103mg/kg, and the hydrolysate obtained after enzymolysis is up to 70mg/kg, which is a potential threat to the safety of consumer. The excessive content of fluoride in Antarctic Krill hydrolysate has become the bottleneck for its further development and utilization. In this paper, three different methods, which are nanofiltration,electrodialysis and chemical-biological method, are studied aimed at removing excessive fluoride from Antarctic krill hydrolysate and provide technical support for the development and application of it. The main conclusions are as follows:1) Nanofiltration technology is explored as a method for defluorination of Antarctic krill hydrolysate. Effects of the concentration of material (dilution factor), operating pressure and operating time on defluorination results are tested while keeping other operating conditions invariant. The optimum operating conditions were finalized as : operating time of 10min, operating pressure of 1.6Mpa, 1.5 times diluted Antarctic krill as sample.Operating nanofiltration under optimum conditions, batch constant volume nanofiltration process is proceeded and eventually the fluoride content in the hydrolysate is reduced from 49.97mg/kg to 2.45mg/kg. Nanofiltration can desalt while removing fluoride from the antarctic krill hydrolysate, but Considering its amino nitrogen and total nitrogen loss during pretreatment, it leads to great nutrients loss, which is amino nitrogen loss of 15.7% and total nitrogen loss of 22.5%. The nutrient loss is serious, making it of less potential for nanofiltration to be applied to defluorination of Antarctic krill hydrolysate.2) The technology of electrodialysis is tested to remove the fluoride from Antarctic krill hydrolysate. The effect of different operating voltage, flow rate and temperature on defluorination results of hydrolysate was researched while mainting other variables stable and the cleaning of ion-exchange membrane is preliminarily studied. Results show that increase operating voltage is benificial for defluorination, but high voltage may easily lead to the occur of concentration polarization and cause great loss of amino nitrogen. Improving the flow rate is conductive to reduce defluorination time and enhance current efficiency. Raising the temperature is helpful to speed up the process of electrodialysis. Finally, the best operating conditions for the electrodialysis is confirmed as: constant operating voltage 20V, flow rate 60L/h and temperature 30¡À2¡æ.Operating electrodialysis under the best condition can reduce the fluoride content of the Antarctic krill hydrolysate from 58.97 mg/kg to 1.25 mg/kg. Electrodialysis has great defluorination capacity, but nutrients loss of the hydrolysate afer electrodialysis, which is amino nitrogen 14.9% and total nitrogen 19.0%, is slightly too high. And the advantage of electrodialysis is that it can desalt while removing fluoride, which is to the benefit of further seasoning.3) The technology of adding calcium chloride to the hydrolyzate to lower the fluoride content is studied. Based on single factor experiment, the condition of defluoridation is optimized through response surface methodology and a mathematical model is established for removing excessive fluoride from the Antarctic krill hydrolysate with calcium chloride depostion. Model fits very well . Results of defluorination rate could be predicted well and truly by the mathematical model.Optimized by response surface, the defluoridation condition is optimal when adding amount of calcium chloride was 1.38% (m/v), initial pH was 9.0, reaction temperature was 20¡æ. Under that condition, the fluoride content of Antarctic krill hydrolysate after defluoridation is 8.3mg/L. The actual defluorination rate is 97.89% of theoretical rate and a good coherence lied between them.A biological defluorination agent is found based on adding calcium chloride method, and it can remove residual fluoride in the Antarctic krill hydrolysate with high efficiency after calcium deposition. It breaks the limit of 20-30mg/kg by calcium deposition and lowered the fluoride content of hydrolysate to ~ 2mg/kg. Besides, the defluoridation process had insignificant effect on amino nitrogen and total nitrogen content of the hydrolyzate with amino nitrogen loss of 6.8% and total nitrogen loss of 9.6%. Removing fluoride from Antarctic krill hydrolysate with this chemical-biological technology is simple, short time-consuming, and effective, suggesting that this would be an ideal method for defluoridation of Antarctic krill hydrolysate.
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