Emprego de membrana na separação de células de Zymomonas mobilis em bioprocessos associados para a produção de etanol e ácido lactobiônico

Abstract

Zymomonas mobilis, anaerobic bacteria, metabolize glucose, fructose or sucrose generating equimolar amounts of CO2 and ethanol. Glucose behave as an inducer of glucose - fructose oxidoreductase (GFOR) and glucono -- lactonase (GL), periplasmic enzymes from Z. mobilis, promoting the oxidation of aldoses in aldonic acids and reduction of ketoses to polyols. To obtain high yields of biomass and ethanol in cultures of Z. mobilis cells and subsequent use in the bioconversion step, cell recycling techniques, with emphasis on the use of membranes have been employed. In this work we compared the recycling of cells through ceramic and polymeric (hollow fiber) membranes with trials in batches by cuts of fermentation and centrifuged batch systems. Earlier, tests for setting the activation time and the cell culture the nutrients needed, defining the shape of inoculation and percentage of inoculum used were performed and, as a preliminary test, the determination of glucose concentration to be employed in the tests. The activation of the cell culture of choice for testing the continuity of the percentage was 10% of cells, where 12 hours of culture, 4 g.L-1 were obtained with the use of purified yeast extract. Furthermore, the results indicated that under the conditions evaluated, among inoculum sizes tested (5-20%), increased ethanol production was obtained with 15% by volum - compared to the final volume of medium - or the concentrated biomass. To conduct the test fermentations was definitely the best condition with respect to the substrate concentration 80 g.L-1, where the tests, it was possible to obtain 3,4 g.L-1 of cells within 6 hours of cultivation. The recycle of cells by centrifugation of the cells showed that this system can recycle the increase in both cell growth and ethanol production. Similar results were obtained in tests with cell recycle in batches by cut of fermentation. In recycled through membranes with respect to cell growth, average increase of 35% was observed when the concentration of the cells performd with the ceramic membrane and no increase was observed when used polymeric membranes. Because of this, the cells in recycled ceramic membrane were subjected to the test of bioconversion and the results show performance of 46% in terms of production of lactobionic acid.