Violeta Valcheva

Dr. Violeta Valcheva


Research Focus & Metrics

Academic Career Length

16Years (2011-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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19 January 2021 in Biomolecules
Verified
Journal Article
Open access
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Milka MilevaMilka Mileva
Milka Mileva
Yana IlievaYana Ilieva
Yana Ilieva
GJGabriele Jovtchev
Gabriele Jovtchev
SGSvetla Gateva
Svetla Gateva
Maya Margaritova ZaharievaMaya Margaritova Zaharieva
Maya Margaritova Zaharieva
Hristo NajdenskiHristo Najdenski
Hristo Najdenski
Plants from the Rosacea family are rich in natural molecules with beneficial biological properties, and they are widely appreciated and used in the food industry, perfumery, and cosmetics. In this review, we are considering Rosa damascena Mill., Rosa alba L., Rosa centifolia L., and Rosa gallica L. as raw materials important for producing commercial products, analyzing and comparing the main biological activities of their essential oils, hydrolates, and extracts. A literature search was performed to find materials describing (i) botanical characteristics; (ii) the phytochemical profile; and (iii) biological properties of the essential oil sand extracts of these so called “old roses” that are cultivated in Bulgaria, Turkey, India, and the Middle East. The information used is from databases PubMed, Science Direct, and Google Scholar. Roses have beneficial healing properties due to their richness of beneficial components, the secondary metabolites as flavonoids (e.g., flavones, flavonols, anthocyanins), fragrant components (essential oils, e.g., monoterpenes, sesquiterpenes), and hydrolysable and condensed tannins. Rose essential oils and extracts with their therapeutic properties—as respiratory antiseptics, anti-inflammatories, mucolytics, expectorants, decongestants, and antioxidants—are able to act as symptomatic prophylactics and drugs, and in this way alleviate dramatic sufferings during severe diseases.

23 March 2023 in Pharmaceuticals
Verified
Journal Article
Open access
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Yoanna TenevaYoanna Teneva
Yoanna Teneva
Rumyana SimeonovaRumyana Simeonova
Rumyana Simeonova
VVVioleta Valcheva
Violeta Valcheva
VAViolina T. Angelova
Violina T. Angelova
Tuberculosis is an extremely serious problem of global public health. Its incidence is worsened by the presence of multidrug-resistant (MDR) strains of Mycobacterium tuberculosis. More serious forms of drug resistance have been observed in recent years. Therefore, the discovery and/or synthesis of new potent and less toxic anti-tubercular compounds is very critical, especially having in mind the consequences and the delays in treatment caused by the COVID-19 pandemic. Enoyl-acyl carrier protein reductase (InhA) is an important enzyme involved in the biosynthesis of mycolic acid, a major component of the M. tuberculosis cell wall. At the same time, it is a key enzyme in the development of drug resistance, making it an important target for the discovery of new antimycobacterial agents. Many different chemical scaffolds, including hydrazide hydrazones and thiadiazoles, have been evaluated for their InhA inhibitory activity. The aim of this review is to evaluate recently described hydrazide-hydrazone- and thiadiazole-containing derivatives that inhibit InhA activity, resulting in antimycobacterial effects. In addition, a brief review of the mechanisms of action of currently available anti-tuberculosis drugs is provided, including recently approved agents and molecules in clinical trials.

19 November 2023 in Molecules
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Journal Article
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Antoaneta TrendafilovaAntoaneta Trendafilova
Antoaneta Trendafilova
PSPlamena Staleva
Plamena Staleva
ZPZhanina Stoyanova Petkova
Zhanina Stoyanova Petkova
VIViktoria Ivanova
Viktoria Ivanova
YEYana Evstatieva
Yana Evstatieva
SSSvetlana Simova
Svetlana Simova
Dry rose extract (DRE) obtained industrially by aqueous ethanol extraction from R. damascena flowers and its phenolic-enriched fraction, obtained by re-extraction with ethyl acetate (EAE) were the subject of this study. 1H NMR of DRE allowed the identification and quantitation of fructose and glucose, while the combined use of HPLC-DAD-ESIMS and HPLC-HRMS showed the presence of 14 kaempferol glycosides, 12 quercetin glycosides, 4 phenolic acids and their esters, 4 galloyl glycosides, 7 ellagitannins, and quinic acid. In addition, the structures of 13 of the flavonoid glycosides were further confirmed by NMR. EAE was found to be richer in TPC and TFC and showed better antioxidant activity (DPPH, ABTS, and FRAP) compared to DRE. Both extracts displayed significant activity against Propionibacterium acnes, Staphylococcus aureus, and S. epidermidis, but showed no activity against Candida albicans. Toxicity tests on normal human skin fibroblasts revealed low toxicity for both extracts with stronger effects observed at 24 hours of treatment that were compensated for over the following two days. Human hepatocarcinoma (HepG2) cells exhibited an opposite response after treatment with a concentration above 350 µg/mL for EAE and 500 µg/mL for DRE, showing increased toxicity after the third day of treatment. Lower concentrations were non-toxic and did not significantly affect the cell cycle parameters of either of the cell lines.

29 June 2023 in Foods
Verified
Journal Article
Open access
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RHRamize Hoxha
Ramize Hoxha
YEYana Evstatieva
Yana Evstatieva
DNDilyana Nikolova
Dilyana Nikolova
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.

1 October 2018 in Biocatalysis and Agricultural Biotechnology
Verified
Journal Article
Closed access
TGTeodora Georgieva
Teodora Georgieva
YEYana Evstatieva
Yana Evstatieva
VSValentin Savov
Valentin Savov
SBSvetlana Bratkova
Svetlana Bratkova
DNDilyana Nikolova
Dilyana Nikolova

17 June 2023 in Microorganisms
Verified
Journal Article
Open access
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NANikola Atanasov
Nikola Atanasov
YEYana Evstatieva
Yana Evstatieva
DNDilyana Nikolova
Dilyana Nikolova
Oral probiotic lactic acid bacteria can exhibit antagonistic activities against pathogens associated with diseases in the oral cavity. Therefore, twelve previously isolated oral strains were assessed for antagonistic evaluation against selected oral test microorganisms Streptococcus mutans and Candida albicans. Two separate co-culturing analyses were performed, where all tested strains showed the presence of antagonistic activity and four strains, Limosilactobacillus fermentum N 2, TC 3-11, and NA 2-2, and Weissella confusa NN 1, significantly inhibited Streptococcus mutans by 3–5 logs. The strains showed antagonistic activity against Candida albicans, and all exhibited pathogen inhibition by up to 2 logs. Co-aggregation capability was assessed, showing co-aggregative properties with the selected pathogens. Biofilm formation and antibiofilm activity of the tested strains against the oral pathogens were assayed, where the strains showed specificity in self-biofilm formation and well-expressed antibiofilm properties by most of them above 79% and 50% against Streptococcus mutans and Candida albicans, respectively. The tested LAB strains were assayed by a KMnO4 antioxidant bioassay, where most of the native cell-free supernatants exhibited total antioxidant capacity. These results show that five tested strains are promising candidates to be included in new functional probiotic products for oral healthcare.