| The SA/CS-CaCl2/PMCG microcapsule is a novel system which is formed by a polyelectrolyte complexation of sodium alginate (SA) and cellulose sulfate (CS) with poly(methylene co-guanidine) (PMCG) in the presence of CaCl2. In this paper, the effects of important parameters in preparation, such as the substituting degree of CS . the concentrations and ratio of CS and SA concentration of PMCG the solution used in the whole preparation process and reaction tune, on the characteristics of the microcapsules were studied. The following results were obtained: Firstly, the substituting degree 0.36 of CS was more suitable for the preparation of the microcapsules. Secondly, there was an optimum concentration for SA and CS, where the microcapsules showed the best mechanical strength. Moreover, the diameters of the microcapsules decreased with the increase in the concentration of SA or CS. Thirdly, with the raising of the concentration of PMCG or extending of reaction time in the PMCG solution, the diameters of the capsules decreased and the membrane thickness increased whereas the mechanical strength enhanced firstly and then decreased.The diffusion property of the microcapsules is very important for the application of the microcapsules in immobilized microorganism culture. The diffusion processes of nine solutes with low molecular weight in three different microcapsules prepared by using PMCG concentrations of 0.2% 0.5% and 1.5% were measured, which included glucose lactose lactic acid ethanol L-glutamic acid L-lysine L-tryptophan L-phenylalanine and L-tyrosine. What's more, the diffusion coefficients in the membrane and the combined coefficients in three lands of microcapsules of the solutes were determined. The results showed that the solutes could permeate into the capsules freely only that the diffusion coefficients in the membrane and the combined coefficients of the solutes were smaller than those in pure water, respectively.Meanwhile, the diffusivities of PEG with different molecular weight in above three different microcapsules were studied. As a result, the molecular weight cut-off of three different microcapsules were determined respectively, which were approximately 2000. Therefore, mechanical property and mass transfer property of SA/CS-CaCl2/PMCG microcapsules could be decoupled. It allows us to adjust mechanical strength and membrane permeability independently.E. coli and S. cerevisia were chosen as the model microorganism. The effects of PMCG free microcapsules and the immobilized culture on the growth of E. coli and S. cerevisia were studied. Though PMCG had great toxicity to both microorganisms, free capsules had little effects on them. What's more, the encapsulated cells underwent almost the same growth process as free cells. As a whole, SA/CS-CaCl2/PMCGmicrocapsules have good biocompatibility to both microorganism and are a suitable method of cell encapsulation.Encapsulated S. cerevisia was chosen to be cultured sequentially 14 batches. The glucose consumption ethanol production and cell density of each batch respectively. The results showed high cell density could be reached easily and thehighest cell density was 1.04 X 1010L-1 microcapsules. Time of fermentation could be reduced and the production capacity could be improved markedly. Tie ethanol concentration was as high as 51.64 g.L-1 medium. It showed again that SA/CS-CaCl2/PMCG microcapsules were an ideal immobilization method.The compatibility of SA/CS-CaCl2/PMCG microcapsules to Bacillus subtilis wasstudied. Based on these experiments, the encapsulated Bacillus subtilix was cultured sequentially 4 batches to produce nattokinase with molecular weight of about 28kDThe highest cell density in the SA/CS-CaCl2/PMCG microcapsules was four to fivetimes higher than that in tree culture. The fermentation time was reduced markedly from 100 hours to about 50 hours. The maximum nattokinase activity was reached to 2804UK.ml-1 microcapsules, which was more higher than that in free culture Therefore , it showed ma...
|
PDF Full Text Request