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. 2023 Aug;45(8):931-938.
doi: 10.1007/s10529-023-03384-w. Epub 2023 May 25.

Determining the linear correlation between dielectric spectroscopy and viable biomass concentration in filamentous fungal fermentations

Atli Magnússon  1   2 , Jari Pajander  3 , Gürkan Sin  3   4 , Stuart Stocks  3   4
Affiliations

Determining the linear correlation between dielectric spectroscopy and viable biomass concentration in filamentous fungal fermentations

Atli Magnússon et al. Biotechnol Lett. 2023 Aug.

Abstract

Objectives: Dielectric spectroscopy is commonly used for online monitoring of biomass growth. It is however not utilized for biomass concentration measurements due to poor correlation with Cell Dry Weight (CDW). A calibration methodology is developed that can directly measure viable biomass concentration in a commercial filamentous process using dielectric values, without recourse to independent and challenging viability determinations.

Results: The methodology is applied to samples from the industrial scale fermentation of a filamentous fungus, Acremonium fusidioides. By mixing fresh and heat-killed samples, linear responses were verified and sample viability could be fitted with the dielectric [Formula: see text] values and total solids concentration. The study included a total of 26 samples across 21 different cultivations, with a legacy at-line viable cell analyzer requiring 2 ml samples, and a modern on-line probe operated at-line with 2 different sample presentation volumes, one compatible with the legacy analyzer, a larger sample volume of 100 ml being compatible with calibration for on-line operation. The linear model provided an [Formula: see text] value of 0.99 between [Formula: see text] and viable biomass across the sample set using either instrument. The difference in ∆C when analyzing 100 mL and 2 mL samples with an in-line probe can be adjusted by a scalar factor of 1.33 within the microbial system used in this study, preserving the linear relation with [Formula: see text] of 0.97.

Conclusions: It is possible to directly estimate viable biomass concentrations utilizing dielectric spectroscopy without recourse to extensive and difficult to execute independent viability studies. The same method can be applied to calibrate different instruments to measure viable biomass concentration. Small sample volumes are appropriate as long as the sample volumes are kept consistent.

Keywords: Dielectric spectroscopy; Fermentation; Sensor calibration; Viable biomass.

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Conflict of interest statement

None.

Figures

Fig. 1
Fig. 1
Comparison of measured CDW and ΔC. Dielectric spectroscopy of certain samples is measured in the Viable Cell Analyzer and others using the annular probe. No single sample is measured on both instruments
Fig. 2
Fig. 2
Differences in permittivity increment (ΔC) at different dilution levels. Figure 2a Shows a single sample in the stationary phase measured on the Viable Cell Analyzer at an increment of approx. 0.1 fresh sample mass fraction. Figure 2b shows the permittivity increment of three selected samples to represent different fermentation phases at different dilution levels, measured on the Annular Probe
Fig. 3
Fig. 3
Determination of hidden relation between viable biomass and ΔC after applying the viable fraction corrections on CDW measurements. Two independent calibrations are obtained depending on the measurement device used for ΔC
Fig. 4
Fig. 4
The difference in ΔC when measuring the same fresh samples with different sample volumes when using the annular probe. Viable biomass is calculated using the linear correlation calibrated with the 2 mL samples measured with the annular probe
See this image and copyright information in PMC

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