The applicability of two lactic acid bacterial strains with probiotic potential and bioprotective properties as additions in the starter culture in yogurt fermentation was examined. The studied strains, Lactobacillus delbrueckii subsp. bulgaricus KZM 2-11-3 and Lactiplantibacillus plantarum KC 5-12, inhibited the growth of Kluyveromyces lactis, Kluyveromyces marxianus, and Saccharomyces cerevisiae. The strain L. delbrueckii subsp. bulgaricus KZM 2-11-3 directly inhibited Escherichia coli. The important characteristics for the quality of the yogurt product, such as physicochemical parameters during fermentation and storage, rheological characteristics, and sensory changes during the storage of samples were determined. The yogurt samples with the strains did not differ in most parameters from the control yogurt with the commercial starter. The added strains showed stable viability in the yogurt samples during storage. The yogurt sample with L. delbrueckii subsp. bulgaricus KZM 2-11-3 and the sample with both strains based on the total evaluation were very similar to the control yogurt with the commercial starter. Using these strains as probiotic supplements to enrich the starter cultures in yogurt production will contribute to developing new products with benefits to human health.

The use of antibiotics is a major problem everywhere around the globe and in step with this, there's currently an increased public and scientific interest. Microbial resistance is a vital issue for the organizations like EFSA, WHO, FDA, and FAO because it is developing rapidly and is an increasingly serious health concern within the world. Microbial resistance comes as a result of continuous exposure of microorganisms to antibiotics. Lactic acid bacteria (LAB) constitute a really important group of microorganisms that can inhabit different conditions and environments, as the different parts of the gastrointestinal tract of humans and animals, and are an important element of the microbiota of fermented foods. The FDA and EFSA authorities have given them the status referred to as GRAS (Generally Recognized as Safe) and QPS (Qualified Presumption of Safety). Continuous exposure of LAB to environments with antibiotics may prompt them to become an intrinsic or extrinsic reservoir of genes accountable for antibiotic resistance. Knowledge of antibiotic susceptibility of bacteria with probiotic potential is important. Also, it's essential to define their resistance profile. Ten newly isolated strains from traditional fermented foods were used for determining the antibiotic resistance profile. The resistance to antibiotics varied among the examined strains and a few of the antibiotics resulted in complete resistance. Chromosomal DNA of LAB was analyzed for the antibiotic resistance genes. Only five of eight vancomycin-resistant strains have shown that they contain the resistance gene in chromosomal DNA. None of the genes that determined the resistance to other antibiotics have been detected in chromosomal DNA.

Studies of newly isolated strains of lactic acid bacteria (LAB) are a good basis for expanding the potential for their applications in functional foods, probiotic food supplements, and other probiotic products. They exhibit various functional properties, including such with antiviral activity. Probiotic strains can manifest their antiviral effects by various mechanisms, including direct interaction with viruses, production of antiviral compounds, or immune system modulation. Ten newly isolated LAB strains from traditional fermented food products have been tested for the determination of their antiviral activity. This study was performed to evaluate the effect of cell-free supernatants (CFSs) from the studied strains for the effect on viral replication of Human alphaherpesvirus—HHV-1 and HHV-2 as well as for direct virucidal activity. The CFSs of the LAB strains were used in non-toxic concentrations of 25%, 6.25%, and 1.6%. No direct virucidal activity was observed in tested CFSs, but five of the strains observed a well-defined effect of viral replication inhibition with the selective index (SI) from 4.40 to >54. For two of these five strains, Lactobacillus delbrueckii subsp. bulgaricus KZM 2-11-3 and Lactiplantibacillus plantarum KC 5-12 strong activity against HHV-2 with a selective index (SI) over 45 was detected, which is a good basis for further research.

Production of the traditional yoghurt, white-brined cheese, and yellow cheese, named “kashkaval”, in the Bulgarian region determines everyday consumption and health benefits for the local population. Аrtisanal dairy products and their autochthonous microbiota are a promising source for the research and creation of new minimally treated, but safe, functional and delicious food. The species from Lactobacillaceae are used in different fermentation technologies, improving the structure, taste, and aroma of the final products. These products possess a prolonged shelf life due to the biopreservative capabilities of the lactic acid bacteria (LAB) strains, their positive health impact, and many physiological functions in the body. This chapter examines the traditional and modern technologies for the production of typical Bulgarian dairy products. Based on the studies of artisanal products, different LAB species from non-starter microbiota are presented, which contribute to the organoleptic qualities of the products and their beneficial properties. The research focus is aimed at the evaluation of various functional characteristics of non-starter strains, such as metabolic activity and food biopreservation. The long-term goal is to study the tradition to create new functional formulas that are the desired and effective factors for health and longevity.