Produccion De Xilitol

JOURNAL OF BIOSCIENCE AND BIOENGINEERING Vol. 98, No. 3, 228–230. 2004

Microbial Xylitol Production from Corn Cobs Using Candida magnoliae
KIYOSHI TADA,1 JUN-ICHI HORIUCHI,1* TOHRU KANNO,2 AND MASAYOSHI KOBAYASHI1
Bioprocess Engineering Laboratory, Department of Chemical System Engineering, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan1and InternationalStudents Center, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507, Japan2
Received 27 May 2004/Accepted 25 June 2004

Microbial production of xylitol from corn cobs using Candida magnoliae was experimentally investigated. Approximately 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. To removeinhibitors from the hydrolysates, charcoal pellets were found to be effective in selectively removing the inhibitors from the hydrolysates without affecting xylose concentration. C. magnoliae was successfully cultivated using the treated corn cob hydrolysate, resulting in the production of 18.7 g-xylitol/l from 25 g-xylose/l within 36 h.
[Key words: corn cobs, hydrolysis, Candida magnoliae, xylose,xylitol, agricultural wastes]

Xylitol has attracted considerable attention in the food and pharmaceutical industries because it has useful characteristics, including its use for the prevention of dental caries, as a sugar substitute for insulin-independent diabetics, and as a natural food sweetener. Xylitol is currently produced on an industrial scale by a catalytic reduction (hydrogenation) ofxylose obtained from wood sources such as white birches. However, alternative processes have been extensively explored because of the high production cost and environmental impact associated with the excessive utilization of natural wood sources. Microbial xylitol production from agricultural wastes containing hemicellulose could be a possible candidate because it has the potential to realizecheaper production of xylitol with low environmental impact by the effective utilization of renewable resources such as agricultural wastes (1, 2). Among various agricultural wastes, corn cobs are regarded as a promising agricultural resource for microbial xylitol production because corn is widely cultivated, and corn cobs are rich in hemicellulose but are not effectively utilized. In microbial xylitolproduction from corn cobs, the cobs are first hydrolyzed to produce xylose from hemicellulose by acid hydrolysis and the corn cob hydrolysate is then used as the medium for xylitol fermentation by xylose-utilizing yeasts (3). Therefore, to evaluate the feasibility of microbial xylitol production from corn cobs, it is essential to examine the hydrolysis conditions of corn cobs and the xylitolproduction yield using the hydrolysates. Furthermore, it is known that furfural and its derivatives, which strongly inhibit yeast growth, are inevitably generated during the hydrolysis of corn cobs. Therefore, it is also necessary to remove these inhibitors to maximize xylose production. In
* Corresponding author. e-mail: horiuchi@betta.chem.kitami-it.ac.jp phone: +81-(0)157-26-9415 fax:+81-(0)157-24-7719
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this study, microbial xylitol production from corn cobs using Candida magnoliae, which has the ability to convert D-xylose to xylitol under microaerobic conditions (3), was experimentally examined in terms of the hydrolysis conditions of corn cobs, the removal of inhibitors, and the xylitol production yield from corn cobs. C. magnoliae FERM P-16522; AIST, Tsukuba) was usedthroughout the study. The strain was grown on an agar slant containing 3 g of malt extract, 3 g of yeast extract, 5 g of peptone, 10 g of glucose and 20 g of agar per liter at 30°C for 24 h and maintained at 4°C. The pH of the agar slant was around 7. Preculture was carried out by two steps to ensure the reproducibility of the experiments. The preculture medium contained 25 g of xylose, 1 g of Casamino...