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Discovering growth patterns of lactic acid bacteria in fermentations by NIR

Carina Svendsen 1 ; Thomas Skov 1 ; Frans van der Berg 1
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A desire for more efficient and less time-consuming methods to monitor and control fermentation processes is seen in the industry. By measuring the critical process parameters, such as physical, chemical and biological process conditions, in real time, it is possible to control productivity and ensure high product quality. Several lactic fermentations are carried out with mixed cultures of lactic acid bacteria. In yoghurt production milk is fermented by the bacteria Streptococcus thermophiles (ST) and Lactobacillus bulgaricus (LB). These two species are known to interact with each other, for example by stimulating each other’s growth by the exchange of metabolites (Sieuwerts et al. 2008). To our knowledge these interactions have not previously been examined by high-frequency real-time methods, therefore this study explores interactions and growth patterns of ST and LB by NIR.

The outcome of lab-scale yoghurt fermentations (working volume of 11 liters) monitored by on-line NIR spectroscopy showed promising outcomes, which might be able to provide a real time measure for the lactic acid bacteria (LAB) growth pattern. The PCA-modelled data measured over time provided an increasing trend during fermentation time with a reproducible small interruption in the rising trend observed at time 1.9 h into the fermentation. It was speculated what is causing the small bump and for this reason several direct, conventional methods are used to verify and interpret the observed NIR-outcome.

This study confirms that the first-order instrument NIR-spectroscopy is a powerful analytical tool in fermentation processes since distinctive signals in the spectrum such as molecule specific vibrations can be used to quantify the chemistry directly compared to conventional measurements such a pH and redox potential. This allows following principal profiles over time which gives the opportunity to monitor the fermentation process with a more comprehensive understanding (Svendsen et al. 2015). A related advantage is the ability to detect unexpected behavior based on differing spectral outcomes and even follow the interactions between the bacteria during the fermentation process.

References
Sieuwerts, S., de Bok, F. A. M., Hugenholtz, J. and van Hylckama Vlieg, J. E. T. (2008): Unraveling Microbial Interactions in Food Fermentations: from Classical to Genomics Approaches. Applied and Environmental microbiology. Vol. 74:16, pp. 4997-5007.
Svendsen, C., Skov, T. and van den Berg, F. (2015): Monitoring fermentation processes using in-process measurements of different orders. Journal of Chemical Technology and Biotechnology. Vol.90:2, pp. 244-254.