Browsing by Author "Stoyanova A."
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Item Antimicrobial active packaging paper based on dill weed essential oil(2020-01-01) Kostova I.; Lasheva V.; Georgieva D.; Damyanova S.; Stoyanova A.; Stefanov S.; Gubenia O.Antimicrobial active packaging based on dill weed essential oil (DWEO) was investigated. Three types of packaging paper (100% bleached pulp 40 g/m2, 100% unbleached pulp 40 g/m2, and 100% recycled paper weighing 70 g/m2) were analysed. The antimicrobial activity was tested against the Gram-positive bacteria Staphylococcus aureus ATCC 6538 and Bacillus subtilis ATCC 6633; the Gram-negative bacteria Escherichia coli ATCC 8739, Pseudomonas aeruginosa ATCC 9027 and Salmonella abony NTCC 6017; the yeast Saccharomyces cerevisiae ATCC 2601 and Candida albicans ATCC 10231; and the fungal strain Aspergillus brasiliensis ATCC 16404. The activity of the bleached paper treated with DWEO against moulds (Aspergillus brasiliensis) and yeasts (Candida albicans) during the five-day study period decreased from 100 to 47%, against Gram-positive bacreria (Staphylococcus aureus and Bacillus subtilis) decreased from 100 to 69%, and against Gram-negative bacteria (Salmonella abony and Escherichia coli) decreased from 76 to 12%. Unbleached paper, treated with DWEO, had stronger antimicrobial potential against Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), compared to other test microorganisms. Recycled paper treated with DWEO showed fungicidal activity.Item APPLICATION POSSIBILITIES OF BIOMASS FROM FENNEL FRUITS(2023-01-01) Nikolova М.; Pencheva M.; Dimov M.; Bozadzhiev B.; Lazarov L.; Damyanova S.; Lasheva V.; Stoyanova A.; Yavorov N.During the processing of fennel fruits (Foeniculum vulgare Mill.) for obtaining essential and vegetable oils, biomass is released. It is mainly used as an additive for feeding or as an organic fertilizer. The aim of this research is to investigate the possibilities of using biomass obtained during the processing of fruits from harvest 2020 and 2021 as a biosorbent of Cr (VI) from aqueous solutions or as a biofuel. The two biomasses were milled and the final fractions obtained by sieve analysis (between 384 and 413 μm) were analyzed. The FTIR spectrum was recorded as 4000 - 400 с-1. Both biomasses act as biosorbent under the following conditions: pH 1.0, agitation speed 300 rpm, adsorbent dose 1.05 g L-1, initial Cr (VI) concentration 80 mg L-1, temperature 30°C. The energy indices used in the assessment of fennel fruit biomass potential as conditional biofuel were calculated: calorific value (15783.40 - 15968.16 kJ kg-1), density (464.19 - 582.91 kg m-3), and heat equivalent (250.05 - 317.68 kJ m-3)Item CHARACTERIZATION OF ACTIVE PAPER PACKAGING MATERIALS WITH CORIANDER ESSENTIAL OIL (CORIANDRUM SATIVUM L.)(2020-01-01) Kostova I.; Lasheva V.; Georgieva D.; Damyanova S.; Fidan H.; Stoyanova A.; Gubenia O.This study aims to investigate the antimicrobial activity of paper-based packaging materials including coriander (Coriandrum sativum L.) essential oil. Three types of packaging papers (bleached, unbleached, and recycled) are treated with an essential oil and then stored for 2 h, 24 h, and 5 days. The antibacterial activity of coriander oil is tested against Gram-positive bacteria (Staphylococcus aureus ATCC 6538 and Bacillus subtilis ATCC 6633); Gram-negative bacteria (Escherichia coli ATCC 8739, Pseudomonas aeruginosa ATCC 9027, and Salmonella abony NTCC 6017); an yeast (Candida albicans ATCC 10231), and a fungal strain (Aspergillus brasiliensis ATCC 16404). Ahigh fungicidal potential is observed in case of all packaging materials. The antimicrobial action of the bleached paper coated with coriander oil against Gram-positive bacteria during the five-day storage period decreases slightly from 100 % - 94 % to 79 % - 81 %.Item COMPARATIVE ANALYSIS OF ANTIBACTERIAL ACTIVITY AND PHYSICOCHEMICAL PROPERTIES OF PEPPERMINT AND CORNMINT ESSENTIAL OILS AND THEIR MAIN COMPOUND MENTHOL(2023-01-01) Gandova V.; Fidan H.; Iliev I.; Lasheva V.; Stankov S.; Stoyanova A.; Yavorov N.The aim of the present paper was to study and present a comparative analysis of the antibacterial activity and physicochemical properties of commercial mint essential oils from two different species - peppermint (Mentha piperita Huds. (L.)) and cornmint (Mentha arvensis L.). Peppermint oils exhibited weak antibacterial activity, but were more pronounced against Gram-positive bacteria Staphylococcus aureus (1.3 - 2.0 mm) and Gram-negative bacteria Escherichia coli (1.2 - 1.9 mm) and Klebsiella sp. (2.6 mm). The essential oil of the species M. arvensis did not exhibit antimicrobial activity against the tested cultures. L-menthol, which is a commercial sample isolate, exhibited activity against all tested microorganisms, with the exception of Gram-positive bacteria Listeria monocytogenes and Bacillus cereus. The diameter of the inhibition zones was the largest against Gram-positive bacteria Bacillus subtilis (3.4 mm), and the smallest was against Gram-positive bacteria Staphylococcus aureus (1.6 mm) and Gram-negative bacteria Klebsiella sp. (1.4 mm). The surface tension, density and refractive index of different mint essential oils were determined experimentally. The surface energy and surface heat capacity were calculated based on the calculations of surface tension. All experiments and calculations were provided at a temperature range between 6℃ and 30℃. A dependence between surface tension and temperature was not observed.Item Effect of B2O3 on the Structure, Properties and Antibacterial Abilities of Sol-Gel-Derived TiO2/TeO2/B2O3 Powders(2023-10-01) Bachvarova-Nedelcheva A.; Iordanova R.; Stoyanova A.; Georgieva N.; Nemska V.; Foteva T.This paper studies the influence of B2O3 on the structure, properties and antibacterial abilities of sol-gel-derived TiO2/TeO2/B2O3 powders. Titanium(IV) butoxide, telluric(VI) acid and boric acid were used as precursors. Differences were observed in the degree of decomposition of Ti butoxide in the presence of H3BO3 and H6TeO6 acids. The phase transformations of the obtained gels in the temperature range of 200–700 °C were investigated by XRD. Composite materials containing an amorphous phase and different crystalline phases (metallic Te, α-TeO2, anatase, rutile and TiTe3O8) were prepared. Heating at 400 °C indicated a crystalline-to-amorphous-phase ratio of approximately 3:1. The scanning electron microscopy (SEM) analysis showed the preparation of plate-like TiO2 nanoparticles. The IR results showed that the short-range order of the amorphous phases that are part of the composite materials consists of TiO6, BO3, BO4 and TeO4 structural units. Free B2O3 was not detected in the investigated compositions which could be related to the better connectivity between the building units as compared to binary TiO2/B2O3 compositions. The UV-Vis spectra of the investigated gels exhibited a red shift of the cut-off due to the presence of boron and tellurium units. The binary sample achieved the maximum photodegradation efficiency (94%) toward Malachite green dye under UV irradiation, whereas the ternary sample photoactivity was very low. The compositions exhibited promising antibacterial activity against E. coli NBIMCC K12 407.Item Effect of clary sage (Salvia sclarea L.) essential oil on paper packaging materials(2020-01-01) Kostova I.; Lasheva V.; Fidan H.; Georgieva D.; Damyanova S.; Stoyanova A.Introduction. The aim of research to determine the effect of clary sage (Salvia sclarea L.) essential oil on paper packaging materials. Materials and methods. Three packaging materials have been studied based on paper coated with clary sage essential oil. The chemical composition of the clary sage essential oil is determined chromatographically. Antimicrobial effect of essential oil was determined against Gram-positive, Gram-negative bacteria, yeasts, and fungi using the agar diffusion method. Results and discussion. The chemical composition of the clary sage essential oil showed a predominant amount of oxygenated monoterpenes (83.43%), followed by monoterpene hydrocarbons (7.86%), and sesquiterpene hydrocarbons (5.16%). The major components of the clary sage essential oil were linalyl acetate, B-linalool, α-terpineol, limonene, and geranyl acetate that determined the antimicrobial action of the oil. The essential oil exhibited a fungicidal action against the tested molds and yeasts. Its high antimicrobial properties could be probably due to the high content of linalyl acetate (40.31%) and B-linalool (22.72%). Our results showed high fungicidal efficacy for the three types of packaging materials. The suppressive action against C. albicans during the investigated shelf life period was about 100%. It was found a high efficiency of the recycled paper against A. brasiliensis (99.2%-81.9%). It was determined that the bactericidal effect of the tested packaging materials was lower than the Gram-negative bacterium S. abony. Conclusions. Clary sage essential oil could be used as an antimicrobial agent in the food industry due to its antimicrobial properties, in order to improve the quality of the products and extend their shelf life.Item INFLUENCE OF Nb2O5 AND B2O3 ON THE PHOTOCATALYTIC AND ANTIBACTERIAL ACTIVITY OF SOL-GEL DERIVED TiO2 NANOPОWDERS(2024-01-01) Bachvarova-Nedelcheva A.; Iordanova R.; Georgieva N.; Nemska V.; Foteva T.; Stoyanova A.TiO2 based powders containing B2O3 and Nb2O5 were obtained through an aqueous sol-gel method. The as-prepared gels were step wisely heated in the temperature range 200°C - 500°C and subsequently characterized by XRD, IR and UV-Vis analysis. The TiO2 (anatase) is the single crystalline phase which has been detected up to 500°C. Photocatalytic tests showed that the investigated samples possess photocatalytic activity toward Malachite green organic dye and TiO2/Nb2O5 exhibited higher photocatalytic activity than TiO2/B2O3 sample. The compositions exhibited good antimicrobial activity against E. coli NBIMCC K12 407 and Bacillus subtilis NBIMCC 3562.Item PHOTOCATALYTIC AND ANTIBACTERIAL ASSESSMENT OF SOL - GEL DERIVED TiO2/TeO2/ZnO POWDERS(2022-01-01) Bachvarova-Nedelcheva A.; Iordanova R.; Georgieva N.; Nemska V.; Stoyanova A.Two ternary gel compositions containing simultaneously TiO2, TeO2 and ZnO were selected for detailed investigations. The phase transformations of the gels upon the heating were investigated by XRD analysis and it was established that the obtained composites contain an amorphous phase and different crystalline phases: TiO2 (anatase), TiO2 (rutile), a-TeO2 and ZnTeO3, depending on composition. The IR results showed that the short range order of the amorphous phases which are part of the composite materials consist of TiO6, ZnO4 and TeO4 structural units. By UV-Vis spectroscopy was measured the absorption edge of the gels which is about 363 nm and the calculated Eg values are about 3.41 eV. The performed photocatalytic tests showed that the samples possess photocatalytic activity toward Malachite green organic dye. Both compositions exhibited good antimicrobial activity against E. coli K12.Item Photocatalytic properties of ZnO/TiO2 powders obtained via combustion gel method(2013-03-01) Bachvarova-Nedelcheva A.; Iordanova R.; Stoyanova A.; Gegova R.; Dimitriev Y.; Loukanov A.The present study is a continuation of our previous investigations on the ZnO-TiO2 system. By applying different sol-gel methods we proved that the type of precursor and the order of adding the components influence the microstructure of the final product. This study focuses on the combustion sol-gel synthesis and photocatalytic properties of nanosized (∼7-20 nm) ZnO-TiO2 powders. The photocatalytic tests were performed toward two model organic dyes, Malachite Green and Reactive Black 5, in the UV and Vis region. For synthesis of ZnO/TiO2 powders, different precursors such as Zn(NO3)2·6H2O, Zn(CH 3COO)2·2H2O, Ti(OC2H 5)4 and Ti(OC4H9)4 were used. During the combustion process various phases (ZnO, TiO2 - anatase and rutile, ZnTiO3) were obtained. The structure and morphology of the resulting particles were characterized by XRD and SEM analysis. All samples exhibited a good photocatalytic activity in both UV and Vis regions. © 2012 Versita Warsaw and Springer-Verlag Wien.Item Photocatalytic properties of ZnO/TiO2 powders obtained via combustion gel method(2013-03-01) Bachvarova-Nedelcheva A.; Iordanova R.; Stoyanova A.; Gegova R.; Dimitriev Y.; Loukanov A.The present study is a continuation of our previous investigations on the ZnO-TiO2 system. By applying different sol-gel methods we proved that the type of precursor and the order of adding the components influence the microstructure of the final product. This study focuses on the combustion sol-gel synthesis and photocatalytic properties of nanosized (∼7-20 nm) ZnO-TiO2 powders. The photocatalytic tests were performed toward two model organic dyes, Malachite Green and Reactive Black 5, in the UV and Vis region. For synthesis of ZnO/TiO2 powders, different precursors such as Zn(NO3)2·6H2O, Zn(CH 3COO)2·2H2O, Ti(OC2H 5)4 and Ti(OC4H9)4 were used. During the combustion process various phases (ZnO, TiO2 - anatase and rutile, ZnTiO3) were obtained. The structure and morphology of the resulting particles were characterized by XRD and SEM analysis. All samples exhibited a good photocatalytic activity in both UV and Vis regions. © 2012 Versita Warsaw and Springer-Verlag Wien.Item Sol-Gel Obtaining of TiO2/TeO2 Nanopowders with Biocidal and Environmental Applications(2023-02-01) Bachvarova-Nedelcheva A.; Iordanova R.; Naydenov A.; Stoyanova A.; Georgieva N.; Nemska V.; Foteva T.TiO2/TeO2 powders were obtained by an aqueous sol-gel method. Telluric acid (H6TeO6) and titanium butoxide were used as precursors. The as-prepared gel was step-wisely heated in the temperature range 200–700 °C and subsequently characterized by XRD, IR, and UV-Vis analysis and SEM. Mixtures containing TiO2 (anatase), α-TeO2 (paratellurite), and TiTe3O8 were established by XRD as final products, depending on heating temperature. The thermal stability of the obtained gels in the temperature range 100–400 °C was investigated. It was found by IR spectroscopy that the samples heated up to 300–400 °C consist mainly of an organic–inorganic amorphous phase which is transformed into an inorganic one above these temperatures. The microstructure of the gels was verified by scanning electron microscopy (SEM). The photocatalytic degradation of the synthesized nanopowders toward Malachite green organic dye (MG) was examined in order to evaluate the potential applications for environmental remediation. The prepared TiO2/TeO2 samples showed up to 60% decoloration efficiency after 120 min exposure to UV-light. The composition exhibited good antimicrobial activity against E. coli K12. The properties of the obtained material were investigated by the reactions of complete catalytic oxidation of different alkanes and toluene, and it could be suggested that TiO2/TeO2 powders are promising material for use as an active phase in environmental catalysts.Item The influence of nd and sm on the structure and properties of sol-gel-derived tio2 powders(2021-07-01) Bachvarova-Nedelcheva A.; Yordanov S.; Iordanova R.; Stambolova I.; Stoyanova A.; Georgieva N.; Nemska V.TiO2 nanopowders modified by Nd and Sm were prepared using the sol-gel technique. It was found by XRD analysis that the samples containing Sm are amorphous up to 300◦C, while those with Nd preserve a mixed organic-inorganic amorphous structure at higher temperatures (400◦C). The TiO2 (rutile) was not detected up to 700◦C in the presence of both modified oxides. TiO2 (anatase) crystals found at about 400◦C in the Sm-modified sample exhibited an average crystallite size of about 25–30 nm, while doping with Nd resulted in particles of a lower size—5–10 nm. It was established by DTA that organic decomposition is accompanied by significant weight loss occurring in the temperature range 240–350◦C. Photocatalytic tests showed that the samples heated at 500◦C possess photocatalytic activity under UV irradiation toward Malachite green organic dye. Selected compositions exhibited good antimicrobial activity against E. coli K12 and B. subtilis.