Realtime Monitoring of Xylitol Fermentation by Micro-Raman Spectroscopy

The fermentation of xylitol is a promising alternative to conventional chemical processes. Micro-Raman spectroscopy was used to monitor the process involving Candida tropicalis, including the medium and yeast cells during xylitol fermentation. The spectra of the fermentation medium showed that the characteristic xylitol peak at 866 cm(-1) was enhanced from 18 h and that the characteristic xylose peak at 901 cm(-1) gradually diminished as the reaction progressed. The characteristic ethanol peak at 880 cm(-1) indicated the production of by-products. Intracellular biological macromolecules, such as nucleic acids, proteins, lipids, and carbohydrates, were identified in the spectra of yeast cells. The intensity of nucleic acids at 783 cm(-1) reached the highest value after 3 h. The xylose band at 901 cm(-1) and the peaks in the carbohydrate region reached a maximum in the logarithmic phase, indicating the carbohydrate metabolism was the most active. The amide I band located at 1658 cm(-1) indicated the major secondary structure of proteins was alpha-helix; its intensity gradually reduced during the fermentation. The 853 cm(-1) band due to buried tyrosine was predominant at 21 h. In addition, the 1275 cm(-1) band corresponded to the presence of a random coil only at 27 h. These results provided a perspective to understand fermentation and verified the applicability of Raman spectroscopy in xylitol fermentation.