Article

Noninvasive method for monitoring ethanol in fermentation processes using fiber-optic near-infrared spectroscopy.

Department of Chemistry, University of Washington, Seattle 98195.
Analytical Chemistry (impact factor: 5.86). 10/1990; 62(18):1977-82. pp.1977-82
Source: PubMed

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%.

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Keywords

actual ethanol
 
actual yeast fermentations
 
Additional experiments
 
calibration model
 
characterize ethanol
 
ethanol production
 
ethanol/water solutions
 
ethanol/yeast/water mixtures
 
ethanol/yeast/water solutions
 
fiber-optic probe
 
gas chromatographic method
 
glass-wall fermentation vessel
 
good correlation
 
mixture experiments
 
multilinear regression
 
photodiode array spectrometer
 
Pure ethanol/water
 
second-derivative data
 
standard error
 
yeast concentration