Use of NIR-light back-scattering to monitor S. cerevisiae growth on lignocellulosic hydrolysates in the presence and absence of biomass solids

Fermentation cell concentrations are usually monitored using offline methods such as optical density (OD) or dry cell weight (DW), which require either dilution or centrifugation and drying, respectively.  The presence of lignocellulosic solids further complicates cell concentration measurements, and either direct microscopic counts or plate counts must then be used. On-line methods of biomass measurement alleviate some of these restrictions in addition to providing continuous data.  The BE2100 biomass sensor (produced by BugLab LLC) is mounted outside the fermentation vessel, and uses near-infrared light back-scattering measured at multiple source-detector distances to determine the cell concentrations relative to the medium background. In this study, plate count measurements were used to calibrate/validate BE2100 sensor measurements, which accurately tracked cell concentrations across large ranges (from 0.1 to over 100 OD₆₀₀).  The BE2100 sensor was also used to monitor cell growth on lignocellulosic slurries; growth curves were again compared with those obtained from plate counts.  Solids interference was minimized by correcting for baseline scattering prior to inoculation.  BE2100 sensor accuracies and practical limits as a function of background solids concentrations will be presented and discussed.