Fermentation reactions are important for the production of many
valuable products including pharmaceuticals, beverages, and biofuels.
In lignocellulosic ethanol production, biomass feedstocks are
chemically pretreated, hydrolyzed by cellulases and hemicellulases, and
the resulting sugars are fermented by yeast or bacteria to produce
In large-scale production of biocommodities such as ethanol, feedstocks
have a large and often dominant impact on process economics and process
For example, the amount of sugar available to fermentation reactions is
important because in the absence of limiting factors, substrate
availability determines product yield; thus methods to measure sugar
available to a fermentation reaction are potentially valuable for
One approach is to complete a simultaneous saccharification and fermentation (SSF) process 
and to assay residual sugars and inhibitory products such as glucose,
cellobiose, and acetic acid by high performance liquid chromatography
(HPLC), and ethanol concentration by gas chromatograph (GC) or HPLC.
The whole procedure takes about 168 hours according to the SSF protocol
specified by the National Renewable Energy Laboratory (NREL) .
Recently, Weimer et al have developed a higher throughput method to
predict the fermentability of cellulosic biomass to ethanol through in vitro gas production .
In this procedure, fermentations are carried out in sealed serum
bottles, and the gas produced is measured as an indicator of the
digestibility of the cellulosic biomass.
In contrast to full SSF processes, many sugar detection and
quantitation methods can be employed, including chemical reducing sugar
assays and enzymatic assays [6,7].
All of these methods require sampling the fermentation reaction and
measuring sugars in the sample. However, because cellulases and
hemicellulases are product inhibited, simple approaches that only
involve hydrolytic enzymes and a sugar assay (or biosensor) yield low,
non-representative estimates of conversion potential. Determining a
meaningful sugar yield requires that sugars be removed as they are
produced, as is done in SSF processes .
Once a sugar scavenger has been added to the mixture of hydrolytic
enzymes, the problem of product inhibition has been solved, but another
problem replaces it: the sugars produced are consumed as they are
produced, making measurements of sugar concentrations a poor predictor
of total sugar released. For this reason, simply relying on a sugar
assay or a sugar biosensor, such as one described by Lidgren et al ,
will not work. Therefore, our objective was to develop a system that
could be used to monitor glucose catabolism as an indicator of
feedstock convertibility and to demonstrate its application to
monitoring corn stover hydrolysis in a process similar to that used for
lignocellulosic ethanol production. Such a system would be useful for
rapidly screening varieties for suitability as biomass feedstocks in
plant breeding programs and for evaluating different hydrolytic
systems. Furthermore, this system could be used to measure sugar
production in a wide range of other experiments.