Real-time study of the effect of different stress factors on lactic acid bacteria by electrochemical optical waveguide lightmode spectroscopy

Lactic acid bacteria play an important role in the fermentation of different food products. During the fermentation processes, lactobacilli are confronted with many inhibitor factors. These factors by themselves or in combination can influence the growth of lactic acid bacteria and their acidification capacity. The subject of our study was to monitor with a newly developed biosensing technique how the different chemical stress factors influence the survival of lactic acid bacteria. Electrochemical optical waveguide lightmode spectroscopy combines evanescent-field optical sensing with electrochemical control of surface adsorption processes. For optical sensing, a layer of indium tin oxide served as a high refractive index waveguide and as a conductive electrode, as well.

Lactobacillus plantarum 2142 suspended in Jerusalem artichoke syrup was used in the experiments. Electrochemical optical waveguide lightmode spectroscopy measurements were undertaken by using OW 2400c indium tin oxide coated waveguide sensors (MicroVacuum, Budapest, Hungary) and were performed in a flow-injection analyzer system. The bacterial cells were adsorbed in native form without any chemical binding on the surface of the sensor by ensuring polarizing potential (1 V) and were exposed to different concentration of acetic acid/Jerusalem artichoke syrup, lactic acid/Jerusalem artichoke syrup and hydrogen peroxide/Jerusalem artichoke syrup solution for 1 h, respectively, and the effect on bacteria cells was monitored. Results were compared to the traditional micro-assay method, and it can be assumed that after further investigations this new technique could be used in real-time application.