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Wort-based beverages produced by lactic acid fermentation showed high nutritional value and functional properties but their flavor was not well accepted by consumers. Therefore, raspberry (Rubus idaeus L) seed oil in concentration of 0.0375% (v/v) was used in order to improve beverage flavor and to increase its biological value. Fermentation was carried out in bottles (static conditions) and in a stirred tank bioreactor (dynamic conditions) at 25°C. The effect of raspberry seed oil addition was investigated by measuring the content of lactic acid bacteria cells, the pH, the phenolic compounds and the antioxidant activity of the beverages with raspberry seed oil addition and the control sample without oil addition. Results showed that stirring increased fermentation rate but led to a decrease in the phenolic compounds content and the antioxidant activity of the beverages produced. Nevertheless, all beverages can be classified as functional because the concentration of lactic acid bacteria was over 107 cells/mL. Our results indicated that functional lactic acid wort-based beverage with improved biological value and flavour can be produced in static fermentation by adding 0.0375% raspberry seed oil.

Sourdough starter development includes examination of potential strains of lactic acid bacteria (LAB), propionic acid bacteria and yeasts, selection of suitable strains, development of combinations and examination of the relationships between the strains in each combination, selection of symbiotic combinations and their industrial probation to determine their qualities. Three sourdough starter combinations from selected lactobacilli (homo- and heterofermentative species) or selected lactobacilli and propionic acid bacteria were developed. The dynamics of the concentration of viable cells of the strains and the sourdough acidity in the back-slopping process up to the 96th hour were monitored. The rheological properties of the starter sourdoughs were characterized. The main dough obtained with sourdough was stronger, more elastic, the pieces of bread were taller. The developed sourdough starters were tested in the production of wheat, wheat-rye, spelt and spelled bread. The finished bread loaves had softer and lighter crumb, and pleasant and characteristic lactic acid aroma. It has been shown that the different bread types obtained with symbiotic starter sourdoughs had longer shelf life and increased microbiological safety. The best starter combination as well as the optimum concentration of starter sourdough for prevention of bacterial and fungal spoilage for each bread type has been determined.

Bacillus amyloliquefaciens M is a non-pathogenic microorganism with probiotic properties isolated from mineral waters in the village of Yabаlkovo, Haskovo region, for inclusion in the composition of probiotics and probiotic foods. It has high antimicrobial activity against pathogenic bacteria, causing food toxic infections and intoxications, as well as against saprophytic microorganisms - bacteria and fungi, which makes it suitable as a biological preparation for plant protection. In order to perform these functions, it is necessary to obtain a spore concentrate. The composition of the nutrient medium for the cultivation and sporulation of the strain has been determined: MP nutrient broth with the addition of salts, in which the strain grew well and a high sporulation rate of 99% was achieved. Cultivation in a bioreactor has been carried out and the time to achieve a high degree of sporulation has been determined. The kinetic parameters of growth and sporulation of Bacillus amyloliquefaciens M in aerobic batch cultivation with a high concentration of spore forms have also been determined. It has been shown that the sporulation process in this strain starts after 12 h from the cultivation start.

A Lactobacillus strain was isolated from rose blossom of Rosa damascena Mill. and it was identified as belonging to the species Lactobacillus helveticus by the application of physiological-biochemical (API 50 CHL) and molecular-genetic methods (sequencing of the 16S rRNA gene). The presence of a number of probiotic properties of L. helveticus 2/20 was investigated. The strain exhibited high antimicrobial activity against pathogenic microorganisms that cause food toxicoinfections and intoxications. L. helveticus 2/20 survived in the simulated conditions of the gastrointestinal tract – pH = 2 and pepsin, pH = 4.5 and pancreatin and pH = 8 and pancreatin, as well as in the presence of up to 0.3% bile salts, retaining a significant concentration of viable cells. It has been shown that L. helveticus 2/20 cells begin multiplying after removing the extreme conditions. The strain allowed bioreactor cultivation and freeze-drying of the obtained concentrates, with the concentration of active cells in the lyophilic preparations exceeding 1012 cfu/g. The kinetic parameters of the batch cultivation process in a bioreactor with stirring and the maximum growth rate were determined, revealing the possibilities for scaling up of the fermentation process from laboratory to industrial conditions, as well as its management. After further research on the probiotic properties of L. helveticus 2/20, it can be included in the composition of probiotics and functional foods.

Batch cultivation in a laboratory bioreactor with stirring of the lactobacilli strains with probiotic properties Lacticaseibacillus casei ssp. casei G17 and Lacticaseibacillus casei ssp. rhamnosus G16 isolated from pink blossom of Rosa damascena Mill was conducted. The changes in the concentration of viable cells were monitored. The growth kinetics was modeled applying the classic and modified logistic curve model and the maximum specific growth rate (μm) of the studied strains was determined. The classical model of the logistic curve showed higher μm for Lacticaseibacillus casei ssp. casei G17 - 0.133 h-1, compared to Lacticaseibacillus casei ssp. rhamnosus G16 - 0.120 h-1, while the modified logistic curve model predicted comparable maximum growth rates of 0.105 h-1 and 0.101 h-1 for Lacticaseibacillus casei ssp. casei G17 and Lacticaseibacillus casei ssp. rhamnosus G16, respectively. Lacticaseibacillus casei ssp. casei G17 was characterized by a shorter induction period (τa = 0.72 h) and a higher adaptation rate constant (k0 – 0.390 h-1) compared to Lacticaseibacillus casei ssp. rhamnosus G16 (τa=1.66 h; k0=0.110 h-1). The established kinetic parameters show that Lacticaseibacillus casei ssp. rhamnosus G16 needs the addition of growth factors in the fermentation medium that will help to optimize its composition for scaling up the fermentation process.

An interesting property for many probiotic strains is to exhibit antimicrobial activity against pathogenic microorganisms. Therefore, the antimicrobial activity of the potentially probiotic strain Lactobacillus acidophilus L12 against Escherichia coli, Staphylococcus aureus and Salmonella sp. was examined in vitro through co-culturing of Lactobacillus acidophilus L12 with each of the pathogenic strains for 72 h. When cultured individually, all strains reached a final population always exceeding 1012 cfu/mL. When co-cultured with each of the pathogenic strains Lactobacillus acidophilus L12 population always exceeded 1012 cfu/mL, while the bacterial population of the pathogenic strains was reduced in a strain-specific manner. Lactobacillus acidophilus L12 demonstrated the highest inhibitory activity against the two Staphylococcus aureus strains, followed by the two E. coli strains, and the two Salmonella sp. strains tested. The kinetics of the co-culturing process of Lactobacillus acidophilus L12 with each of the test pathogenic strains was modelled using the logistic curve model. The obtained results show the strong antagonistic activity of the potentially probiotic strain Lactobacillus acidophilus L12, thus making it a promising candidate for inclusion in the composition of probiotic preparations and functional probiotic foods.

The antimicrobial activity of potentially probiotic strains is important for their possible application in the development of successful strategies for bio-preservation of different foods. The antimicrobial activity of the potentially probiotic strain Lactobacillus plantarum L4 against the pathogenic bacteria Salmonella abony; Staphylococcus aureus; Escherichia coli and the phytopathogenic fungi Aspergillus niger and Aspergillus flavus was determined using agar-diffusion assay with wells. Lb. plantarum L4 exhibited high antagonistic activity against all test microorganisms included in the study, which was due not only to the production and accumulation of lactic acid and other organic acids, but also to the production of other bioactive substances. The bioactive substances were then submitted to the action of different enzymes. This allowed to observe that they have protein nature, suggesting that they are likely bacteriocins or bacteriocin-like substances. The substances produced by Lb. plantarum L4 did not lose their antimicrobial activity during heat treatment at temperatures above 100 °С for 15 min and they exhibited high inhibitory activity against the test-microorganisms when pH ranged between 4 and 7. After further examination of the properties of the produced antimicrobial compounds, Lb. plantarum L4 can be used in the development of strategies for bio-preservation of different food products.