ACID-HYDROLYSIS OF EUCALYPTUS-GRANDIS CHIPS FOR MICROBIAL-PRODUCTION OF XYLITOL

Acid hydrolysis of the hemicellulosic fraction of eucalyptus chips was influenced by the following parameters: temperature, acid concentrati on, residence and immersion time. The concentrations of sugars (glucos e, xylose, arabinose) and acetic acid varied systematically for all hy drolysis conditions tested. The fermentation of different types of hyd rolysate showed distinct behaviour due to the differences in initial c oncentrations of sugars and acetic acid. Smaller amounts of xylose and acetic acid were obtained under conditions of low temperature and low concentration of sulphuric acid. With respect to xylose/xylitol bioco nversion, the xylose consumption rate ranged from 80% to 94%, irrespec tive of the initial concentration of this sugar in the medium. However , the amount of xylitol produced varied significantly. The highest xyl itol concentration (29.7 g/litre) was found in hydrolysate obtained at the following hydrolysis conditions: temperature (140 degrees C), sul phuric acid concentration (0.5%), residence time (10 min) and immersio n time in acid solution 24 h and treated with CaO. The pH rise during the fermentation of the eucalyptus hydrolysate might be related to ace tic acid consumption by the yeast Candida guilliermondii FTI 20037. (C ) 1998 Elsevier Science Ltd.