Browsing by Author "Danova S."
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Item Enzyme profile of lactobacilli from traditional Bulgarian fermented milk products(2019-01-01) Nemska V.; Danova S.; Georgieva N.In recent years, scientific community has focused the attention on the non-starter lactic acid microbiota of home-made dairy products as a source of new candidate-probiotic strains. Lactic acid bacteria (LAB) and in particular Lactobacillus spp. play a major role in acquiring the specific taste and aroma of the final product during the fermentation. For this purpose, 43 Lactobacillus strains, isolated from traditional Bulgarian katak, curd, yoghurt, white-brined and yellow cheese, were subjected to screening of their enzyme capacity. Twenty-five of the strains were pre-selected for determination of their enzyme profile by API ZYM system. It was established that most of the strains showed high leucine and valine arylamidase, β-galactosidase and α-glucosidase activity. Only a few strains showed N-acetyl-β-glucosaminidase, α-galactosidase, β-glucosidase and Naphtol-AS-BI-phospho-hydrolase activity. Alkaline phosphatase, trypsin, α-chymotrypsin, α-mannosidase, lipase (except L. lactis OC2), β-glucuronidase (except L. salicinus KC2) and α-fucosidase (except L. plantarum BS41 and L. lactis OC2) activity were not observed. In order to complete the obtained results, two qualitative tests for determination of the β-galactosidase and proteolytic activity of more than 30 Lactobacillus strains were also applied. Most of the investigated lactobacilli showed moderate proteolytic activity. According to their β-galactosidase activity, 34 % could be defined as active lactose fermenters, 23 %-as late lactose fermenters and 43 %-could not ferment lactose. The investigated Lactobacillus strains showed strain-specific enzyme capacity.Item Functional characteristics of lactobacilli from traditional bulgarian fermented milk products(2019-01-01) Nemska V.; Logar P.; Rasheva T.; Sholeva Z.; Georgieva N.; Danova S.After oral administration, probiotic lactobacilli meet a number of protection systems in the human body, such as exposure to gastric, pancreatic, and small intestinal juices. Overcoming these detrimental barriers allows living bacteria to adhere to the intestinal epithelium and permanently colonize the gastrointestinal tract (GIT), providing health benefits to the host. Based on this, the transit tolerance of 25 candidate probiotic lactobacilli from katak, yoghurt, and white-brined and yellow cheese to simulated bile and small intestinal juices of variable pH was investigated. To establish their resistance, in vitro model systems based on modified MRS media and a longer duration of action (up to 24 h of incubation) were designed. Six of the strains studied were found to show strain-specific survival capacity with low viability in conditions simulating stomach acidity and high resistance to bile and intestinal juices. In addition, the adherence capability (autoaggregation and hydrophobicity) of the strains was determined. Obtained results allowed to select Lactobacillus strains with high survival ratios while passing through the GIT and good adherence properties, which make them suitable for the development of new probiotics.Item IN VITRO ASSESSMENT OF LACTOBACILLUS SPP. TO GROW IN THE PRESENCE OF DIFFERENT CARBON SOURCES IN THE MEDIUM(2022-01-01) Nemska V.; Danova S.; Georgieva N.The selection of suitable media plays a central role in attempts to improve the production of biomass from lactobacilli and the yield of products during fermentation. For this purpose, the growth capacity of 41 candidate probiotic lactobacilli from katak, yoghurt and white-brined and yellow cheese in the presence of different carbon sources in the medium was investigated. To access their abilities, in vitro model systems based on modified MRS broth, containing different carbon sources (2 % and 5 % (w/v) lactose or 2 % (w/v) glucose, prebiotics (inulin, galactooligosaccharides, glucooligosaccharides and fructooligosaccharides) and 30 % (w/v) sucrose) were designed. It was established that Lactiplantibacillus plantarum S8 and S10 had the highest growth rate in modified MRS with 2 % (w/v) glucose, whereas Lactobacillus delbrueckii subsp. bulgaricus Ro34 showed the highest growth rate in modified MRS broth with 5 % (w/v) lactose. In the presence of modified MRS, containing 20 % (w/v) prebiotics, most Lactobacillus strains showed complete utilisation towards galactooligosaccharides, followed by inulin, fructooligosaccharides and glucooligosaccharides. Seventy-three per cent of strains could grow in the presence of 30 % (w/v) sucrose in the medium and were determined as possible exopolysaccharide producers. In addition, the biofilm-formation capacity of the lactobacilli, cultivated in these media, was tested. Lactiplantibacillus plantarum OC1 and BS32 demonstrated good biofilm-formation in the presence of galactooligosaccharides, whereas Ligilactobacillus salivarius subsp. salicinus KC2 formed stable biofilms in the presence of galactooligosaccharides and fructooligosaccharides.Item ISOLATION AND CHARACTERIZATION OF PEPTIDES FROM MILK AS NATURAL INHIBITORS OF ACE I AND FOOD ADDITIVES(2024-01-01) Yakimova B.; Alexova R.; Dobreva L.; Rainova Y.; Dobrev S.; Danova S.; Angelova S.; Stoineva I.Inhibition of Angiotensin-converting enzyme I (ACE I) is a modern therapeutic approach to treatment of hypertension. In recent years, research into natural ACE peptide inhibitors without side effects has become important. The aim of this study is to isolate and characterize novel bioactive peptides from skim and/or whole cow’s milk fermented with selected lactobacillus strains. Several homo/heterofermentative strains of the Lactobacillus species of dairy origin have been pre-selected and different milk fermented samples have been studied. A protocol for analyses was designed and the milk proteins were separated by centrifugation at 4°C at 10000 × g, with molecular mass cut off (MWCO) membranes of 3 and 10 kDa. The samples with molecular mass below 3 kDa were further separated by ultrafiltration by dialysis cell (cut off membrane 1 kDa) by continuous stirring at room temperature. The milk fractions under 1 kDa molecular mass were characterized by UPLC-MS. The ACE-inhibitory activity was determined using the FAPGG (N-[3-(2-Furyl) acryloyl]-L-phenylalanyl-glycyl-glycine) degradation method. All tested samples (1 kDa) exhibit ACE I inhibitory activity with IC50 in a range of 6 - 37 mg mL-1. In silico logP prediction of selected peptides was used to assess whether lipophilicity of the compounds falls within the so-called “therapeutically relevant pharmacokinetic space”.Item Lactobacillus spp. from traditional Bulgarian dairy products(2016-01-01) Nemska V.; Lazarova N.; Georgieva N.; Danova S.Over the last few years the traditional dairy products have been gaining much more popularity among scientists and consumers. They are a part of the nutritional diet of people since ancient times and are a proven source of lactic acid bacteria (LAB) with confirmed and beneficial effects on human health. LAB are the main cause of lactic acid fermentation and determine the specific properties of the resulting products. Home-made fermented dairy products are a part of the daily diet and tradition is saved in several rural regions of Bulgaria. However, the beneficial microbiota of some of them is poorly characterized. Therefore, any research aimed at the isolation and identification of LAB from traditional foods helps to define the autochthonous microbiota, which is typical for the area/product. With these aims 26 artisanal samples of 4 types Bulgarian dairy products: yoghurt, white-brined cheese, yellow cheese and curd, were collected. Their lactic microflora was studied and 74 pure cultures were isolated. They were identified as Lactobacillus spp. using classical approaches for identification. For this reason further characterization of the created collection of lactobacilli is considered perspective.Item Microbiological, Physico-chemical and Rheological Evaluation of Yoghurts, Fermented with Lactobacilli from Traditional Bulgarian Dairy Products(2021-01-01) Nemska V.; Karsheva M.; Danova S.; Georgieva N.Recently the consumers’ demand for new fermented milk products, combining ingredients with natural origin, good quality and beneficial health effects, increase more and more. For this reason, it is very important to pay particular attention to the strains used as starter cultures or additives during their production. The aim of this study is to investigate the dynamic changes in microbiological, physicochemical and rheological properties of milk, fermented with 9 candidate probiotic lactobacilli during their storage. The influence of 21 days of storage on the microbial count, pH, titratable acidity, lactic acid concentration and rheological parameters was determined. Most fermented milk samples demonstrated high cell viability of the starters used, combined with a slight decrease in pH and a corresponding increase of the titratable acidity during the fermentation process. These parameters remain relatively stable during storage. The rheological tests showed that the fermented milk samples studied demonstrated non-Newtonian behavior, which could be described with Herschel-Bulkley rheological model. The results obtained allowed to select lactobacilli with desired properties: high microbial count, a slight change in the physicochemical properties and a non-Newtonian behavior. The data of this study could be used for the development of new fermented milk products with functional properties.Item Physicochemical parameters and rheological properties of yoghurts during the storage(2013-11-05) Karsheva M.; Paskov V.; Tropcheva R.; Georgieva R.; Danova S.The aim of this study is to investigate the changes in different physicochemical, texture and sensory properties of milk fermented with different strains during the storage. An experimental study of the effect of the storage time on the physicochemical and rheological properties of milk fermented with commercial starter (StLb) and the same starter with a probiotic Lactobacillus salivarius LS adjunct was carried out. The effect of the storage on the pH, titrable acidity, lactic acid concentration, microorganisms count, gel firmness and rheological parameters is investigated. During the fermentation a stable decrease of the pH values and increase in the titrable acidity was observed. Through the whole storage period at 4°C (till 28th day) the both fermented milks kept stable rheological and organoleptic properties. This determines the fermented milk as a suitable form for oral administration of tested probiotic strain LS. The rheological tests showed that the products studied demonstrated non-Newtonian behaviour, which could be described with Herschell-Bulkley rheological model. A correlation between the model parameters and the results of the penetration test was found. The results of this study can be used in production of new fermented milk products with functional properties.