Optimization of Fermentation Strategies

TABLE 18.2 Effects of Aeration on Xylitol Production from Xylose by Yeasts 

FIGURE 183 Results of the two-subsirate batch culture by Candida twpicalis ATCC 13803 in a 3.5-L fermentor containing 1 L of fermentation medium (10 g/L yeast extract, 20 g/L bactopeptone, 105 g/L xylose, and 32 g/L glucose) at 30°C, pH 6,500 rpm of agitation speed, and 1 vvm of aeration rate., dry cell mass , glucose , xylose O, xylitol ethanol 

For the continuous production of xylitol with high yields, techniques of whole cell immobilization and cell-recycle fermentation have been used. Candida tropicalis cells were immobilized into calcium alginate, polyacrylamide, a cylindrical porous ceramic, and a nonwoven polyester fabric. At a condition to minimize the loss of the immobilized yeast cells, 86.6 g/L xylitol was produced with a xylitol productivity of 

FIGURE 18.5 (a) A diagram of cell-recycle operation system (Bae et al., 2004) and (b) a cell-recycle fermentation of Candida tropicalis ATCC 13803 in YP medium with initial concentration of 30 g/L glucose and 100 g/L xylose (Choi et al., 2000). The yeast cells were recycled with a hollow fiber membrane with 100,000 molecnlar weight cut-off. Feeding solution was composed of 750 g/L xylose, 200 g/L glucose, and 100 g/L yeast extract., dry cell mass , glucose A, xylose O, xylitol arrow, addition of feed solution. 

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