Filamentous moulds are the main spoilage microorganisms, responsible for significant economic losses and several healthy risks in human food chain. The lactic acid bacteria (LAB), especially lactobacilli could be a natural antagonist of these dangerous organisms. In Bulgaria, a very limited data exists on the antifungal activity of LAB microbiota of fermented dairy products. In the present study, four active strains were isolated from traditional fermented curd/yogurt-like product "katak", produced in Bulgaria from centuries. The new isolates KR3, KR4, KR51 and KR53 were identified by API 50 CH biochemical test and different molecular methods (species-specific PCR, RAPD-PCR and 16S rDNA sequence analysis) as Lactobacillus brevis. According to our knowledge, this is the first data on the molecular characterization of the Lactobacillus microbiota of "katak". A broad spectrum of antifungal activity of the four L. brevis KR strains against test-cultures representatives of carcinogenic, toxigenic, deteriorative and allergenic fungi from the genera Aspergillus, Fusarium, Penicillium and Trichoderma was estimated. Strains L. brevis KR3, KR4 and KR51 completely suppress the growth of Penicillium claviforme, Aspergillus awamori and Aspergillus niger. With regard to Aspergillus flavus and Trichoderma viride, a lower and strain-specific inhibitory activity was observed. The antifungal activity of our new L. brevis isolates seems to be a promising advantage of these four strains, suggesting their potential applications in different food technologies as bio-preservative agents against moulds.

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In order for the beneficial effects of sourdough application in breadmaking to take place a proper selection of lactic acid bacteria species and strains, an appropriate technology and effective control of the purity and activity of the selected cultures. Four symbiotic starters for sourdough for the production of bread were developed and probated in a production laboratory using the selected strains Lactobacillus brevis LBRZ7, L. buchneri LBRZ6, L. plantarum X2, L. paracasei RN5, L. sanfranciscensis R and L. fermentum LBRH10 and the probiotic strain Propionibacterium freudenreichii ssp. shermanii NBIMCC 327. The starter sourdoughs that include Propionibacterium freudenreichii ssp. shermanii NBIMCC 327 had greater antimicrobial activity against saprophytic microorganisms: Bacillus subtilis, B. mesentericus, Aspergillus niger, Penicillium sp. and Rhizopus sp., but none of them inhibited the growth of bakery yeasts Saccharomyces cerevisiae. It was established that in order to prevent bacterial spoilage 10% of the selected starter sourdoughs had to be added in the breadmaking process, while for prevention of mold spoilage the necessary amount of starter sourdough had to be between 15% and 20%.The application of the developed starters for the production of wheat bread guarantees longer shelf life and no adverse alterations in the features of the final bread.

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Lactic acid bacteria are widely studied microorganisms and are one of the prevalent groups of bacteria in the oral cavity microbiome. This work aimed to isolate new lactic acid bacterial strains from the human oral cavity and evaluate their characteristics and probiotic potential. Twelve strains were isolated and identified as belonging to several genera in the family Lactobacillaceae. Screening for antimicrobial activity was held, where two of the strains showed antagonistic activity against Streptococcus mutans and most of the strains expressed inhibition against Escherichia coli, Bacillus subtilis, and Bacillus cereus. The ability of the studied strains to autoaggregate and bind to mucin was assessed, showing autoaggregative properties and mucin binding at 5 logs CFU/mL. The survival ability in simulated oral and gastrointestinal conditions and growth dynamics with different gastrointestinal stress factors was studied. Most of the strains showed a good growth potential in the presence of oral and gastrointestinal stress factors. All tested strains exhibited high survival rates in the simulated oral environment, thus having the potential for colonizing the oral cavity and their beneficial properties to be applied. These results are a good basis for continuing the research into these strains so they can be included in new functional products for oral health.