| Fats and oils are important natural resourses due to their renewability and avaliability. Owing to the advantages of regioselectivity, less byproducts in the enzymatic processes, the application of lipases has been the hot topic in the field. However, the high cost of the commercial lipase limited the development and application of lipases. A strain of Candida sp.99-125 was found and the lipase from the strain has been modified by our group. It has been proved that the lipase is of high activity, stability and low cost. The biocatalysis platform of this lipase has been well developed,and has been sucessfully applied to the esterification of various fatty acids.The research on the structured lipids and the regioselectivity of the process should be furthur developed. In addition, the epoxidation of unsaturated fats and oils has also been the hotpot and should also be further developed in the enzymatic field.Based on the issues mentioned above, the aim this research is to carry out the enzymatic production and optimization of sugar alcohol-based fatty acid esters, the human milk fat substitutes (HMFS) and the epoxy fatty aicds by Candida sp. 99-125 lipase. The catalyst efficiency,regioselectivity has been discussed; the the reaction mocroenvironment through basic parameters optimization of the process was established; the regulation of temperature and mass transfer based on the machanism and acyl migration has been finished; and the optimal conditions for different processes corresponding to different products. The main results were demonstrated as below:1.In the production of xylitol fatty acid esters part, the tert-butanol reaction system was first established. A preheating step was introduced to increase the dissovability of xylitol in tert-butanol. By the preheating step,the super-saturated solutions were made and helped to increase the solubility of xylitol in tert-butanol. After optimization of the process, the yield of xylitol esters was 70% in 6h, and in which the 1(5)-O-xylitol monoester was 95%. A solvent-free system of xylitol and capric acid was developed because it has more advantages than solvent systems. In 120 h,the yield of xylitol esters was 70%: 16 % of 1(5)-O-xylitol caprate monoester, 60% of 1,5-O-xylitol caprate diester, and 24% of 1,2,5-O-xylitol caprate triester and 1,3,5-O-xylitol caprate trimester mixture. The insight of the mechanism in this part revealed that the products substitutes mainly depended on the reaction energy barrier and the thermodymatic equilibrium.2.The production of human milk fat substitutes (HMFS) is a challenge due to the special structure of HMFS. By the optimization of the key parameters in the process, like temperatrue, enzyme loading,substrate ratio and additional water contents, combining the acyl migration and regioselectivity in the process, the optimal reaction condition for HMFS was obtained. After purification of the crude products by molecular distillation, the parameters in the purified products could meet the national standard. The yield of the aimed structured lipids was 52-55%, the palmitic acid distributed at sn-2 position in triacylglycerides (TAG) was 55%-59%, and the tripalmitn accounted for 8.4%-9.6% in whole TAGs, and the peroxide value was 1.41-1.89 meq/g.All the values of the key parametrs could well fited the national standard and even better than the requirement of the standard.3.In the production of epoxy fatty acids, the functional group ofCOOH would aggravate the side reactions in the process. In this research,a kinetic model was established in order to study the side reactions in the system. By comparing the reaction rate constants, and energy consumption in the process, the conclusion was reached that the side reaction in the chemical process cannot be completely avoided.A chemo-enzyamtic epoxidation of oleic acid was then studied by application of Candida sp. 99-125 lipase. The epoxy value of the products could reach 4.12% in 10 h at 30 ?. The conversion of epoxy step was 76.58%, and the selectivity of the epoxidation was 0.98. The application of the optimal reaction conditions were used in the epoxidation of Sapindus mukorossi fatty acids. The stability and reliability of the eoxidation process was proved.The comparison of chemo-enzyamtic and chemical epoxidation were compared in the view of reaction conditions, mechanism. The pro and cons of two processes were listed accordingly.In a conclusion, the research on the acyl migration mechanism study,process control in the structured lipids; the solution to solve the side reactions and inhibition of perxide products on lipase was obtained has fulfill of the biocatalysis platform of this lipase and helped it to be more competitive in the application in industries. |
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