title: Noninvasive method for monitoring ethanol in fermentation processes using fiber-optic near-infrared spectroscopy.
abstract: Short-wavelength near-infrared (SW-near-IR) spectroscopy (700-1100 nm) is used for the determination of ethanol during the time course of a fermentation. Measurements are performed noninvasively by means of a photodiode array spectrometer equipped with a fiber-optic probe placed on the outside of the glass-wall fermentation vessel. Pure ethanol/water and ethanol/yeast/water mixtures are studied to establish the spectral features that characterize ethanol and to show that determination of ethanol is independent of the yeast concentration. Analysis of the second-derivative data is accomplished with multilinear regression (MLR). The standard error of prediction (SEP) of ethanol in ethanol/water solutions is approximately 0.2% over a range of 0-15%; the SEP of ethanol in ethanol/yeast/water solutions is 0.27% (w/w). Results from the mixture experiments are then applied to actual yeast fermentations of glucose to ethanol. By use of a gas chromatographic method for validation, a good correlation is found between the intensity of backscattered light at 905 nm and the actual ethanol. Additional experiments show that a calibration model created for one fermentation can be used to predict ethanol production during the time course of others with a prediction error of 0.4%.
authors.affiliation: Department of Chemistry, University of Washington, Seattle 98195.
authors.forename: A G
authors.initials: AG
authors.lastname: Cavinato
authors.forename: D M
authors.initials: DM
authors.lastname: Mayes
authors.forename: Z H
authors.initials: ZH
authors.lastname: Ge
authors.forename: J B
authors.initials: JB
authors.lastname: Callis
mesh_terms: D000431:Ethanol / Q000032:analysis*; D005285:Fermentation; D005336:Fiber Optic Technology; D055100:Optical Fibers; D012542:Scattering, Radiation; D013055:Spectrophotometry, Infrared
chemical_list: D000431:Ethanol