Investigation of the antimicrobial efficacy of some traditional Turkish probiotic beverages

Functional foods have been developed in order to promote good nutrition, improve health, and reduce disease risk, and probiotics-containing products are a typical example of these functional foods. Probiotic products have anticarcinogenic, antimutagenic, cholesterol lowering, lactose intolerance alleviation effect, and help to modulate the immune system. Besides these beneficial activities, they also have antimicrobial activity which is one of the most important selection criteria for their use in commercial products. Probiotic organisms exhibit beneficial health effects by inhibiting pathogens through the synthesis of various antimicrobial metabolites such as organic acids, hydrogen peroxide and bacteriocins. Probiotic foods constitute a significant part of the functional foods market worldwide. A number of studies have been reported to evaluate the microbiota composition of fermented traditional Turkish beverages and their probiotic properties, but no studies have been encountered which evaluate the antimicrobial activity of the probiotic contents of these beverages. Therefore in our study, microbial compositions of five different fermented traditional Turkish beverages namely boza, kefir, ayran, shalgam juice and hardaliye were examined and the antimicrobial activities of the isolates against standard human pathogens were evaluated. The beverage samples were diluted to 10-6 by a ten-fold serial dilution using % 0,5 sterile peptone water. Aliquots were taken from the serially diluted samples and plated on the appropriate selective media for the isolation of probiotic microorganisms. deMan Rogosa and Sharpe (MRS) agar for lactobacilli; Bifidobacterium Selective Medium (BSM) agar for bifidobacteria; M17 agar for lactic streptococci, and Sabouraud Dextrose Agar (SDA) was used for yeast isolation. Lactic acid bacteria and bifidobacteria were isolated under anaerobic conditions at 37 °C with 72 hours incubation in an anaerobic jar containing GasPak. Lactic streptococci and yeasts were isolated at 28-30 °C under aerobic conditions with 72 hours and 3-5 days incubation respectively. A total of 22 presumptive probiotic microorganisms were isolated from the analysed beverage samples. The bacterial isolates were confirmed to be catalase negative and Gram positive. They were further identified by bacterial artificial chromosome (BAC) data sequencing technique. The morphologically characterized pure isolates were stored at -20 ve -86 ° C in the presence of % 20 glycerol in their respective broth culture media until antimicrobial analyses. The antimicrobial effects of the probiotic isolates against selected common human pathogens were assessed using two different methods viz. spot-on-lawn and agar well diffusion assays. Eighteen isolates displayed varying degrees of antagonistic effects against the tested pathogens. Amongst the obtained isolates, the strongest antimicrobial effects were exhibited by those probiotic strains isolated from boza and kefir. Spot-on-lawn method was found to be more effective than the agar well diffusion method in the evaluation of antimicrobial effects. Although antimicrobial activity is one of the most important criteria in the selection of probiotics, it is not sufficient for their use as probiotic additives. Other probiotic selection properties should be examined in further studies.