Online monitoring and characterization of flocculating yeast cell flocs during continuous ethanol fermentation

Abstract

Both intrinsic and observed kinetic investigations for those ethanol fermentations using self-flocculated yeast strains have been hindered by the lack of real online monitoring techniques and proper characterization methods for the flocs. An optical detecting technique, the focused beam reflectance measurement probe developed by Lasentec (Redmond, WA) was inserted into a fermentor to monitor the floc chord length distributions. Using a simulating system composed of the floc-buffer suspensions, the total floc chord length counts per second were directly correlated with the floc biomass concentrations so that the floc biomass concentrations can be in situ detected. Furthermore, a characterization method of the flocs was established by properly weighted treatments of the detected floc chord length distributions. When a real yeast floc ethanol fermentation system was detected during its intrinsic kinetic investigations in which the floc size needed to be controlled at a level of micrometer scale to eliminate inner mass transfer limitations, it was found and validated that CO(2) produced during fermentation exerted significant disturbances. By applying 1/length-weighted treatment, these disturbances were effectively overcome.

Effect of the size of yeast flocs and zinc supplementation on continuous ethanol fermentation performance and metabolic flux distribution under very high concentration conditions

“…Independent experiments were carried out by controlling the average size of the yeast flocs at 100, 200, and 300 mm (F1, F2, and F3), respectively, with the focused beam reflectance online measurement (FBRM) system (Model M400L, Lasentec, Redmond, WA) previously established for the yeast flocs (Ge et al, 2005b). Different average sizes of the yeast flocs were obtained by adjusting the mechanical stirring speed of the bioreactor, which were monitored by FBRM to be stable within the size of 101 AE 8 mm (F1), 193 AE 9 mm (F2), 310 AE 17 mm (F3), and 297 AE 16 mm (F3Zn), respectively.…”

“…Different from regular free yeast cells which are in the size of several micrometers, yeast flocs are irregular in shape, not uniform in size and dynamic between aggregation of small flocs and breakdown of large ones during cell culture and fermentation, which are controlled by physical, chemical, hydrodynamic, and kinetic conditions (Ge et al, 2005b). Furthermore, yeast cells are subject to severe stresses under VHC fermentation conditions (Pham and Wright, 2008), and viability of individual cells in yeast flocs is not homogeneous (Smukalla et al, 2008).…”

Use of focussed beam reflectance measurement (FBRM) for monitoring changes in biomass concentration

“…Ge et al [13] successfully correlated the total FBRM counts with the floc biomass concentration in the range of 4.03 and 64.58 g DCW L -1 for self-flocculating yeast, SPSC 01. They successfully employed FBRM to characterize the size of flocs in a continuous ethanol fermentation system.…”

“…It is currently used extensively in the chemical and pharmaceutical industries for a range of applications where particle analysis is important such as in the monitoring of crystallisations [9], determination of nucleation kinetics [10,11] and tracking of flocculation behaviour [12]. The FBRM system has also been employed for biomass measurement by other groups in yeast cell fermentations [13], as well as in plant cell cultures [14].…”

Optimization of Insect Cell Based Protein Production Processes - Online Monitoring, Expression Systems, Scale Up

“…Although the probe has already been utilized for offline characterization of microbial [95][96][97][98] and plant cell systems [99][100][101], applications in cell culture processes are not yet reported. The latest version of the G400 FBRM system distributed by Mettler-Toledo is fully autoclavable and therefore allows the integration of this technology even in cell culture processes.…”