Xylose is one of the most abundant monosaccharide in nature. It is the second in amount behind glucose. This monosaccharide is a building block for hemi cellulose, one of three major components in wood plants and natural fibers. The research for xylose fermentation is now widely conducted, mainly to convert this renewable resource to fuel alcohols. Another important product is xylitol, a sugar alcohol derived from xylose that is used for artificial sweetener. In this research, we conducted experiments of fermenting xylose using yeast Candida utilis in 1.25 liter batch culture. The variables were aeration rate and pH controlling. The aeration rates used were 0 and 500 ml/min, whereas the pHs were controlled at 5.0 with addition of KOH and without control. The results obtained shows that the yeast C. utilis posses the capability of xylose assimilation and fermentation during both aerated and non-aerated cultured even though the growth in aerated culture is better. In the culture without controlled pH, the growth is the best. The plausible explanation is that during the growth at very low pH, the yeast might reduce the metabolic flux toward organic acids production. It could increase the flux to the building block for cell growth. The highest xylitol production is at 0.5 g/l is obtained during non-aerated culture with controlled pH. This is because the limited oxygen level could inhibit the further utilization of xylitol in the xylose degradation pathway.
Arina Handayani, Sylvia Sunoto, Yalun Arifin
Presented in Seminar Rekayasa Kimia dan Proses 2005, Universitas Diponegoro, Semarang.