Cunha M A A, Rodrigues R C B, Santos J C, Converti A, da Silva S S
Department of Biotechnology, Faculty of Chemical Engineering, Lorena, Rodovia Itajubá-Lorena, Km 74.5, C.P. 116, 12600-970, Lorena-SP, Brazil.
Curr Microbiol. 2007 Feb;54(2):91-6. doi: 10.1007/s00284-005-0465-4. Epub 2007 Jan 5.
Xylose-to-xylitol conversion was investigated in a bench-scale bioreactor using Candida guilliermondii cells entrapped within polyvinyl alcohol-hydrogel beads in a system operated in repeated-batch mode with cell recycling. Yeast-viable cells were immobilized in the support using the freezing-thawing method. Bioconversion assays were performed in a stirred tank reactor operated at 400-rpm agitation speed, 30 degrees C temperature, and 1.04-vvm air flow rate. The system was explored during six successive cycles, and a small decrease in the conversion performance in the fifth cycle was observed, but the biocatalytic activity of the microorganism was recovered in the sixth cycle after washing the particles. During the process, the hydrogel beads maintained their shape and size without appreciable deterioration. Xylitol production, yield factor, and volumetric productivity increased with progressive recycling of cells and achieved their maximum values (P(F) = 39.7 g l(-1); Y(P/S) = 0.77 g g(-1); Q(P) = 0.53 g l(-1) h(-1), respectively) after the third cell recycling, probably because of cells' adaptation to the medium.
在一个小型生物反应器中，使用 entrapped 在聚乙烯醇 - 水凝胶珠粒中的季也蒙毕赤酵母细胞，在一个采用细胞循环的重复批次模式运行的系统中研究了木糖向木糖醇的转化。使用冻融法将酵母活细胞固定在载体中。在搅拌罐反应器中进行生物转化测定，搅拌速度为 400 rpm，温度为 30℃，空气流速为 1.04 vvm。该系统在连续六个循环中进行了探索，观察到在第五个循环中转化性能略有下降，但在洗涤颗粒后，微生物的生物催化活性在第六个循环中恢复。在该过程中，水凝胶珠粒保持其形状和大小，没有明显劣化。随着细胞的逐步循环，木糖醇产量、产率因子和体积生产率增加，在第三次细胞循环后达到最大值（分别为 P(F) = 39.7 g l(-1); Y(P/S) = 0.77 g g(-1); Q(P) = 0.53 g l(-1) h(-1)），这可能是因为细胞适应了培养基。
