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  • Modelling real-time simultaneous saccharification and fermentation of lignocellulosic biomass and organic acid accumulation using dielectric spectroscopy

    Author: David N. Bryant, Stephen M. Morris
    Publication date: 02-10-2011
    Abstract
    Dielectric spectroscopy (DS) is routinely used in yeast and mammalian fermentations to quantitatively monitor viable biomass through the inherent capacitance of live cells; however, the use of DS to monitor the enzymatic break down of lignocellulosic biomass has not been reported. The aim of the current study was to examine the application of DS in monitoring the enzymatic saccharification of high sugar perennial ryegrass (HS-PRG) fibre and to relate the data to changes in chemical composition. DS was capable of both monitoring the on-line decrease in PRG fibre capacitance (C = 580 kHz) during enzymatic hydrolysis, together with the subsequent increase in conductivity (G = 580 kHz) resulting from the production of organic acids during microbial growth. Analysis of the fibre fractions revealed >50% of HS-PRG lignocellulose had undergone enzymatic hydrolysis. These data demonstrated the utility of DS biomass probes for on-line monitoring of simultaneous saccharification and fermentation (SSF).
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  • The application of a novel biomass sensor to the control of yeast pitching rate

    Author: Boulton C. A., Maryan P.S. and Loveridge D.
    Publication date: 01/01/70
    Abstract
    Accurate methods of pitching rate is essential for consistent fermentation performance. traditional methods, typically dispensing a metered volume of yeast slurry of pre determined suspended solids are unreliable and difficult to automate. methods based in-line optical measurements are inherently inaccurate since viable and dead cells are not distinguished. These problems are overcome by a novel biomass sensor which measures the dielectrical permittivity of yeast suspensions at radio-frequencies. The probe is responsive to viable cells only, over an extended range and is unaffected by gas bubbles and trub. the application of the device to in-line automatic pitching rate control is described
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  • Application of dielectric spectroscopy for monitoring high cell density in monoclonal antibody producing CHO cell cultivations

    Author: Laszlo Parta, Denes Zalai, Sandor Borbely, Akos Putics
    Publication date: 25-06-2013
    Abstract
    The application of dielectric spectroscopy was frequently investigated as an on-line cell culture monitoring tool; however, it still requires supportive data and experience in order to become a robust technique. In this study, dielectric spectroscopy was used to predict viable cell density (VCD) at industrially relevant high levels in concentrated fed-batch culture of Chinese hamster ovary cells producing a monoclonal antibody for pharmaceutical purposes. For on-line dielectric spectroscopy measurements, capacitance was scanned within a wide range of frequency values (100-19,490 kHz) in six parallel cell cultivation batches. Prior to detailed mathematical analysis of the collected data, principal component analysis (PCA) was applied to compare dielectric behavior of the cultivations. PCA analysis resulted in detecting measurement disturbances. By using the measured spectroscopic data, partial least squares regression (PLS), Cole-Cole, and linear modeling were applied and compared in order to predict VCD. The Cole-Cole and the PLS model provided reliable prediction over the entire cultivation including both the early and decline phases of cell growth, while the linear model failed to estimate VCD in the later, declining cultivation phase. In regards to the measurement error sensitivity, remarkable differences were shown among PLS, Cole-Cole, and linear modeling. VCD prediction accuracy could be improved in the runs with measurement disturbances by first derivative pre-treatment in PLS and by parameter optimization of the Cole-Cole modeling.
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  • Developments in Using Off-Line Radio Frequency Impedance Methods for Measuring the Viable Cell Concentration in the Brewery

    Author: J. P. Carvell, G. Austin, A. Matthee, K. Van de Spiegle, S. Cunnungham and Claire Harding
    Publication date: 01/01/70
    Abstract
    The radio frequency (RF) impedance method of measuring yeast concentration is accepted in many breweries around the world. The method relies on detecting the capacitance of the yeast cell membranes and gives a rapid linear response over a wide concentration range. The main application for the RF impedance method is for measuring the concentration of viable yeast in slurries; however the data presented also illustrate the use of the method for monitoring the yeast concentration during production fermentations. The variability of yeast growth during small-scale fermentations was also investigated for two lager strains. Batches pitched on the basis of capacitance were compared with those pitched using the traditional basis of wet weight. The small-scale fermentations pitched on the basis of capacitance were more reproducible than the fermentations pitched on the basis of wet-weight yeast. Good correlation was found between the capacitance and hemocytometer techniques in most smallscale and production vessels when the cell diameter was above 6 μm.
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  • Recent Developments in Using Scanning Radio-Frequency Impedance Measurements on Cell Culture Processes

    Author: John P Carvell, Aditya Bhat, Pareshkumar M Patel, Gerard H Markx
    Publication date: 01/01/70
    Abstract
    The viable cell concentration is of prime importance in monitoring cell culture manufacturing processes. Of the available online biomass assays, the radio-frequency impedance (RFI) method has some clear advantages for manufacturing because it is an unambiguous reflection of viable cell biovolume rather than the total number of cells. This allows RFI to be used to control feeding rates or to maintain a constant level of biomass within the bioreactor. RFI is also suitable for measuring the live cell density in bioreactors when the cells are attached to microcarriers and to inert discs. Traditional RFI-based systems measure the capacitance at either one frequency (typically 0.5 MHz) or in a dual frequency mode. However, scanning the capacitance in a frequency range, typically between 0.1 and 20 MHz, also makes it possible to measure other important parameters such as the cell size, the cell membrane capacitance, and the cell interior conductivity online.3,4 Online measurement of such properties can provide useful information regarding the physiological state of the cells, which can assist in better understanding and controlling the fermentation or cell culture process. In this article, we introduce the concept, theory, and challenges of applying RFI frequency scanning using the Aber Biomass Monitor (Aberystwyth, UK) to cell culture processes, and show examples of how additional process parameters can be derived.
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