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Effect of culture conditions such as pH. temperature, agitation speed and oxygen transfer rate on xylitol production from xylose by Candida parapsilosis ATCC 21019 mutant was investigated in a jar fermentor. The initial concentration of xylose was fixed at 50 g/ℓ in this experiment. When pH was increased, cell growth and xylose consumption rate were increased, but maximum xylitol production was shown in the range of pH 4.5 and 5.5 with a yield of 0.68 g/g-xylose. The optimal temperature for xylitol production was determined to be 30℃. Considering the importance of dissolved oxygen tension, for xylitol production, the effect of oxygen transfer rate coefficient (k_La) on fermentation parameters was carefully evaluated in the range of 20∼85 hr^(-1) of k_La (corresponding to 100∼300 rpm of agitation speed). The xylitol production was maximized at 30 hr^(-1) of k_La (150 rpm). A higher oxygen transfer rate supported better cell growth with lower xylitol yield. It was determined that maximum xylitol concentration, xylitol yield and productivity was 35.8 g/ℓ, 71.6% and 0.58 g/ℓ∼hr, respectively, at 30 hr^(-1) of k_La. In order to further increase xylitol productivity, ferementation using the concentrated biomass(20 g/ℓ) was carried out at the conditions of pH 4.5, 30℃ and 30 hr^(-1) of oxygen transfer rate. The final xylitol concentration of 40 g/ℓ was obtained at 18 hours of culture time. From this result, it was calculated that xylitol yield was 80% on the basis of xylose consumption and volumetric productivity was 2.22 g/ℓ∼hr which was increased by 3∼4 fold compared with 0.5∼0.7 g/ℓ-hr obtained in a normal fermentation condition.
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