Antimicrobial and immunomodulatory potential of various Lactobacillus reuteri strains is closely connected to their metabolite production profile under given cultivation conditions. We determined the in vitro production of antimicrobial substances such as organic acids, ethanol, and reuterin by four strains of L. reuteri (L. reuteri E, L. reuteri KO5, L. reuteri CCM 3625, and L. reuteri ATCC 55730). All studied L. reuteri strains showed the ability to produce lactic acid, acetic acid, and ethanol with concominant consumption of glucose and together with phenyllactic acid-a potent antifungal compound-with concominant consumption of phenylalanine. The reuterin production from glycerol was confirmed for all analyzed lactobacilli strains except L. reuteri CCM 3625. Production of organic acids, ethanol, and reuterin is significantly involved in antimicrobial activity of lactobacilli which was determined using the dual-culture overlay diffusion method against six indicator bacteria and five indicator moulds. In comparison to the referential L. reuteri ATCC 55730, the highest inhibition potential was observed against Escherichia coli CCM 3988 and Pseudomonas aeruginosa CCM 3955. Among analyzed indicators of moulds, the growth of Alternaria alternata CCM F-128 was the most inhibited by all four analyzed L. reuteri strains. Finally, the immunomodulatory potential of analyzed lactobacilli were proven by the determination of the in vitro production of biogenic amines histamine and tyramine. L. reuteri CCM 3625 was able to produce tyramine, and L. reuteri E and L. reuteri KO5 were able to produce histamine under given cultivation conditions.

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Amperometric biosensors based on a gold planar electrode and on two types of nanocomposite electrodes consisting of multi-walled carbon nanotubes for the determination of L-malic acid designed for wine-makers were developed. The biosensors designed for wine-makers were constructed by immobilization of L-malate dehydrogenase and diaphorase within chitosan layers on the surface of the electrodes. The coenzyme NAD+ and the electrochemical mediator ferricyanide were present in the measuring solution. The current resulting from re-oxidation of produced ferrocyanide was measured at a working potential of +300 mV against an Ag/AgCl reference electrode. The biosensor based on a gold electrode showed linearity over the range 10–520 µM with a detection limit of 5.41 µM. Calibration curves for biosensors utilizing nanocomposites were obtained both with the linear range of 10 to 610 µM. The detection limits were 1.57 and 1.77 µM, respectively. The biosensors showed satisfactory operational stability (no loss of sensitivity after 30 consecutive measurements) and storage stability (90% of the initial sensitivity after one year of storage at room temperature). The results obtained from measurements of wine samples were in a good correlation with the standard HPLC method. Satisfactory biosensor sensitivity, specificity and stability allowed their successful commercialization.