(140b) A Spectrophotometric Method for Quantitative Determination of Xylose In Fermentation Medium

The characterization of released sugars during fermentation is very important. Difficulty arises in the availability of a rapid, inexpensive and sensitive method for the detection of target sugars because fermentation broths are a complex mix of nutrients, waste products and cell debris. Since many of the ingredients are non-chromophoric and can't be detected by absorbance, target sugars can be identified from the rest of the fermentation medium by its conversion to a chromophoric substance that can be measured spectrophotometrically. A method involving UV spectrophotometry for the quantitative determination of xylose as the target sugar was developed. This widely known method is based on the dehydration of xylose to furfural in acidic medium with heat. The furfural produced condenses with orcinol in the presence of Fe³⁺ as catalyst to form a colored complex that can be measured by UV spectrophotometry. Factors affecting xylose concentration measurements such as acidic medium concentration, heating time and amount of Fe³⁺ catalyst were investigated. A continuous scan revealed the working wavelength to be 671 nm. The effect of other components in the fermentation broth was found to be negligible. Absorbance shows a linear relationship to xylose in the range of 100-500 mg/L. The xylose concentrations from actual fermentation were determined with the method and compared with YSI 2700, an enzyme electrode employed for xylose measurements and HPLC-ELSD method, a common technique for measuring xylose. Dilution is necessary for comparable xylose concentrations with YSI 2700 and HPLC.