Host: The Society of Chemical Engineers, Japan
Microbial xylitol production from corn cob hydrolysates using Candida magnoliae, which has an ability to convert xylose to xylitol under microaerobic condition, was investigated to enhance the utilization of corn cobs. About 25 g-xylose/L solution was obtained from 100 g-corn cobs/L solution by hydrolysis using 1.0 % sulfuric acid at 121°C for 60 min. The hydrolysates were then used for xylitol production, however, the cell growth was strongly inhibited due to the byproducts including furfural and hydroxymethylfurfural generated during the acid hydrolysis of corn cobs. Therefore, charcoal pellets, which were produced from waste mushroom medium, were employed as adsorbent in order to remove the inhibitors in the corn cob hydrolysates. By the charcoal pellets treatment, only the inhibitors were selectively removed from the corn cob hydrolysates without affecting xylose concentration. Using the treated corn cob hydrolysates, C. magnoliae was successfully cultivated, resulting in the production of 18.7 g-xylitol/L from 25 g-xylose/L within 36 h. Since the xylitol production by C. magnoliae were strongly influenced by dissolved oxygen (DO) concentration, the effects of oxygen transfer rate (OTR) on xylitol production was then investigated using a computer-controlled jar fermentor. The results showed that the xylitol production occurred only when the OTR ranged from 0.5 mmol-O2/L·h to 16.5 mmol-O2/L·h. Maximum xylitol yield (0.75 g/g) and productivity (0.2 g/L·h) were obtained at the OTRs of 0.5 mmol-O2/L·h and 4.9 mmol-O2/L·h, respectively.
