Santos J C, Carvalho W, Silva S S, Converti A
Department of Biotechnology, Faculty of Chemical Engineering of Lorena, Rodovia Itajubá-Lorena, km 74.5, P.O. Box 116, 12600-970 Lorena, SP, Brazil.
Biotechnol Prog. 2003 Jul-Aug;19(4):1210-5. doi: 10.1021/bp034042d.
Cells of Candida guilliermondii immobilized onto porous glass spheres were cultured batchwise in a fluidized bed bioreactor for xylitol production from sugarcane bagasse hemicellulose hydrolyzate. An aeration rate of only 25 mL/min ensured minimum yields of xylose consumption (0.60) and biomass production (0.14 g(DM)/g(Xyl)), as well as maximum xylitol yield (0.54 g(Xyt)/g(Xyl)) and ratio of immobilized to total cells (0.83). These results suggest that cell metabolism, although slow because of oxygen limitation, was mainly addressed to xylitol production. A progressive increase in the aeration rate up to 140 mL/min accelerated both xylose consumption (from 0.36 to 0.78 g(Xyl)/L.h) and xylitol formation (from 0.19 to 0.28 g(Xyt)/L.h) but caused the fraction of immobilized to total cells and the xylitol yield to decrease up to 0.22 and 0.36 g(Xyt)/g(Xyl), respectively. The highest xylitol concentration (17.0 g(Xyt)/L) was obtained at 70 mL/min, but the specific xylitol productivity and the xylitol yield were 43% and 22% lower than the corresponding values obtained at the lowest air flowrate, respectively. The concentrations of consumed substrates and formed products were used in material balances to evaluate the xylose fractions consumed by C. guilliermondii for xylitol production, complete oxidation through the hexose monophosphate shunt, and cell growth. The experimental data collected at variable oxygen level allowed estimating a P/O ratio of 1.35 mol(ATP)/mol(O) and overall ATP requirements for biomass growth and maintenance of 3.4 mol(ATP)/C-mol(DM).
将季也蒙毕赤酵母细胞固定在多孔玻璃球上，在流化床生物反应器中分批培养，用于从甘蔗渣半纤维素水解产物生产木糖醇。仅25 mL/min的通气速率确保了木糖消耗的最低产量（0.60）和生物量产量（0.14 g(DM)/g(Xyl)），以及木糖醇的最高产量（0.54 g(Xyt)/g(Xyl)）和固定化细胞与总细胞的比例（0.83）。这些结果表明，尽管由于氧气限制细胞代谢缓慢，但主要致力于木糖醇的生产。通气速率逐渐增加至140 mL/min，加速了木糖消耗（从0.36增加到0.78 g(Xyl)/L·h）和木糖醇形成（从0.19增加到0.28 g(Xyt)/L·h），但导致固定化细胞与总细胞的比例以及木糖醇产量分别降至0.22和0.36 g(Xyt)/g(Xyl)。在70 mL/min时获得了最高木糖醇浓度（17.0 g(Xyt)/L），但特定木糖醇生产率和木糖醇产量分别比在最低气流速率下获得的相应值低43%和22%。消耗的底物和形成的产物浓度用于物料平衡，以评估季也蒙毕赤酵母用于木糖醇生产、通过磷酸己糖途径完全氧化以及细胞生长所消耗的木糖部分。在可变氧气水平下收集的实验数据允许估计P/O比为1.35 mol(ATP)/mol(O)，以及生物质生长和维持所需总的ATP为3.4 mol(ATP)/C-mol(DM)。
