Browsing by Author "Karsheva M."
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Item Antioxidant activity and polyphenolic content of the Bulgarian wild herb cistus incanus L. stored under different conditions(2017-01-01) Dimcheva V.; Karsheva M.Present study investigates the effect of storage (at room temperature and at a frozen state) of Cistus incanus leaves and its hard-coated seeds on the total polyphenol content and the antioxidant capacity in view of the extraction carried out in 50 % ethanol-in water solution. A correlation between the polyphenol content and the antioxidant activity of the leaves stored at room temperature is elucidated. The frozen stored material generates better extraction efficiency and keeps a very high antioxidant activity. This investigation demonstrates that Cistus incanus from Strandja Mountain, Bulgaria is an important source of polyphenols and antioxidant activity. The latter is present in leaves stored for a couple of years. The results from this study contribute to better understanding the extraction process of this non- traditional Bulgarian herb.Item Cistus incanus from strandja mountain as a source of bioactive antioxidants(2018-03-01) Dimcheva V.; Karsheva M.The purpose of the present study is to survey the extraction conditions and explore the antioxidant potential of the wild herb Cistus incanus, which is non-traditional in Bulgarian ethnomedicine and widespread in the Strandja Mountain. The influence of the extraction time (0-500 min) and solvent composition (0-50% ethanol in water) on the polyphenols, flavonoid yields and on the antioxidant capacity of the extracts of leaves, stalks (wood parts) and bud mixture were studied. The antioxidant capacity (AOC) was evaluated by use of scavenging assays of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. Total polyphenol and flavonoid contents were quantified using UV-vis (ultraviolet-visible) spectrophotometry. The optimal yield of the desired components was obtained with 30% ethanol in water solvent at the 390th min of extraction time. In addition, the influence of seasonality (winter and summer Cistus incanus), and of the different aerial parts-hard-coated seeds, buds, and a mixture of leaves and stalks of the wild plant-on the presence of polyphenols, flavonoids, and AOC were investigated. The present work revealed that the high values of polyphenols, flavonoids and the high AOC occurred not only in the summer leaves, but were also found in the winter leaves, hard-coated seeds, buds, and stalks. Based on the obtained results, the Cistus incanus from Strandja Mountain could be an excellent new source of natural antioxidants in food and for the pharmaceutical industries.Item Comparison of citrus peels as a source of valuable components - Polyphenols and antioxidants(2013-11-05) Karsheva M.; Kirova E.; Alexandrova S.; Georgieva S.The aim of this study is to compare some citrus fruits' peels: mandarins and grapefruits, as sources of polyphenolic compounds, to determine the antioxidant activity of the extracts and to find the effect of the operational conditions on the final extract properties. It was found that the both materials are rich of polyphenols and exhibit high antioxidant activity; better results are obtained for the grapefruit peels. The flavonoids' content in both materials studied is quite close. The solid-to-liquid ratio plays an important role in the extraction process. The better results are obtained for the ratio of 1:10. The results of this study confirm that the citrus peels are promising source of natural antioxidants and polyphenols.Item CONVECTIONAL EXTRACTION OF PHENOLIC COMPOUNDS FROM RED FRUITS – CHOKEBERRY (ARONIA) AND ELDERBERRY(2023-01-01) Enchev B.; Karsheva M.; Radoeva R.The aim of this study was to compare the quality of phenolic content and antioxidant capacity of Chokkeberry (Aronia) and Elderberry plants. Characterisation of phenolic compounds was carried out by Folin-Ciocalteau method. Antioxidant activity of Chokeberry (Aronia) and Elderberry products were determined using 2,2-diphenyl-2-picrylhydrazyl (DPPH). All extraction runs were carried out at constant extractive parameters chosen previously - temperature, sample particle size, extraction manner. All analyses were performed spectrophotometrically. This study focuses on the convectional extraction - particularly conventional solid-liquid extraction (conducted via magnetic stirrer) of pre-dried Chokeberry and Elderberry. An investigation of total polyphenol contents (TPC) and total antioxidant capacity (TAC) were done. Extraction takes place at a pre-selected duration of 100 minutes. The extraction was examined with 5 solvents: aqueous solution of ethanol with concentration (20 vol. %; 50 vol. %; 80 vol. % and 96 vol. %) and distilled water. The temperature was kept constant at 40oC.Item Conventional Ultrasound And Microwave-Assisted Extraction Of Phenolic Compounds From Mavrud Grape, Pomace And Seeds(2020-01-01) Chimshirova R.; Karsheva M.; Diankov S.; Hinkov I.This research is dedicated to the valorization of wine industry residual products as a source of valuable compounds of interest to the food, pharmaceutical and cosmetic industries. Whole grape seeds and grape pomace of organic Mavrud of Bulgarian origin, harvested in 2016 were used. The aqueous ethanolic extracts were prepared by three different techniques: conventional extraction via magnetic stirring, ultrasound-assisted extraction (US) and microwave-assisted extraction (MW). Microwaves seemed to be more efficient in extracting the desired substances through the hard shell of the seeds. The polyphenolic content of the seed extracts, expressed as GAE (gallic acid equivalent) was remarkably higher: 58.57 mg GAE g-1 dw (first stage of MW-assisted extraction) compared to the conventional extraction with a magnetic stirrer – 7.03 mg GAE g-1 dw. The results obtained for the US extraction were similar - 49.73 mg GAE g-1 dw, but the processing time in the microwave field was considerably shorter. The US-assisted extraction was not so convenient for the grape pomace extracts - 20.47 mg GAE g-1 dw were obtained for 240 min, compared to 75.02 mg GAE g-1 dw for 20 min in the microwave field. Three analyzes were performed to determine the total polyphenolic content, antioxidant activity and anthocyanin content. The MW-assisted extraction was the most suitable for leaching of polyphenolic compounds and the extracts exhibited a higher antioxidant activity. Contrarily it has been observed that the anthocyanin content of the extracts produced via MW-assisted extraction was lower compared to the conventional and US-assisted techniques. Both techniques revealed time and energy-saving and are considered as eco-procedures.Item Effect of the viscosity ratio on the mass transfer into a spherical drop in liquid-liquid dispersions(2014-01-01) Alexandrova S.; Karsheva M.; Saboni A.; Gourdon C.Numerical solutions of the Navier-Stokes equations of motion and the equations of mass transfer have been obtained for the unsteady state transfer into a spherical drop moving in an unbounded fluid medium of different viscosity. The effect of the viscosity ratio, k, between the dispersed phase and the continuous phase, on the mass transfer into a spherical drop, is investigated for different ranges of viscosity (0 < k < 10), Reynolds number (0 < Re < 100) and Peclet number (0 < Pe < 104).Item Effects of interface contamination on mass transfer into a spherical bubble(2015-01-01) Saboni A.; Alexandrova S.; Karsheva M.A numerical study has been conducted to investigate the effects of contamination on mass transfer into a spherical bubble. The influence of the contamination on the mass transfer inside the bubble was studied for different ranges of dispersed phase Reynolds numbers (0.1 < Red < 10), Schmidt numbers (0.7Item EPR SPECTROSCOPY INVESTIGATION ON THE ANTIOXIDANT EFFICACY OF SAMBUCUS NIGRA L (DRY FLOWERS/BLOSSOM) EXTRACT(2023-01-01) Petkova-Parlapanska K.; Diankov S.; Karsheva M.The present study aims to evaluate the antioxidant efficacy and the lipid peroxidation degree of Sambucus nigra L. (S. nigra) blossom extract after induction of biotic stress. Dry stained extracts of S. nigra flowers were analyzed by direct and indirect in vitro EPR spectroscopy. The antioxidant activity of the extract was assessed by DPPH analysis, and the inhibition of lipid peroxidation - by PBN-spin adduction, after UV-B and thermal stress. The direct EPR stable radical structures presence was established either in non-irradiated and UV-B irradiated samples. Furthermore, as before and after UV-B and thermal biotic stress, S. nigra showed well-expressed scavenging abilities and protective properties against reactive oxygen and nitrogen species such as superoxide radicals (•O2̅ ), hydroxyl radicals (•OH), and reduced lipid peroxidationItem EXTRACTION OF VALUABLE COMPONENTS FROM WINERY’S BY-PRODUCTS THROUGH SOXHLET EXTRACTION. EFFECT OF OPERATIONAL PARAMETERS ON PRODUCT YIELD AND QUALITY(2022-01-01) Radoeva R.; Karsheva M.; Enchev B.This study focuses on the Soxhlet extraction of pre-dried at 50oC grape marc and grape seeds from Mavrud grapes cultivated in 2016 and 2018. An investigation of total polyphenol contents (TPC), total anthocyanins (TA) and totalantioxidant capacity (TAC) was done. Soxhlet extraction takes place at a pre-selected duration of 180 minutes. Theeffect of the solid-to-liquid ratio was examined with 2 solvents: ethanol-in-water solution (50/50 vol.) and pure methanol.The temperature was kept constant at 220oC. The contents of obtained extracts were characterized by HPLCItem Extraction of valuable compounds from Bulgarian St. John'S Wort (Hypericum Perforatum L.). Antioxidant capacity and total polyphenolic content(2019-01-01) Chimshirova R.; Karsheva M.; Diankov S.; Hinkov I.Ethnobotanical reports claim that St. John's Wort has important biological and chemical properties and can be used for the treatment of many diseases. Most studies related to Hypericum perforatum are focused on its antidepressant effects, but it has also been examined for wound healing, antiviral and antimicrobial activity. In this study the experiments are carried out at ambient temperature at constant stirring rate. The solvent is a 50 vol. % water-ethanolic solution, the solid-to-liquid ratio is 1:10 g mL-1, and the average particle size is 0,75 mm. The results show that the antioxidant capacity and the total polyphenolic content are superior compared to those reported by other authors. The liquid extracts have been stored in a refrigerator for 9 months, then they have been examined again and it has been noticed that their antioxidant effect and total polyphenolic content are preserved. After drying at 50°C, storage and regeneration, the quality of the extracts did not change, which is important issue for long term transportation and storage.Item Heat transfer from a moving fluid sphere with internal heat generation(2014-01-01) Alexandrova S.; Karsheva M.; Saboni A.; Gourdon C.In this work, we solve numerically the unsteady conduction-convection equation including heat generation inside a fluid sphere. The results of a numerical study in which the Nusselt numbers from a spherical fluid volume were computed for different ranges of Reynolds number (0 < Re < 100), Peclet number (0 < Pe < 10000) and viscosity ratio (0 < κ < 10), are presented. For a circulating drop with Re → 0, steady creeping flow is assumed around and inside the sphere. In this case, the average temperatures computed from our numerical analysis are compared with those from literature and a very good agreement is found. For higher Reynolds number (0 < Re < 100), the Navier-Stokes equations are solved inside and outside the fluid sphere as well as the unsteady conduction-convection equation including heat generation inside the fluid sphere. It is proved that the viscosity ratio κ (κ = = μd/μc) influences significantly the heat transfer from the sphere. The average Nusselt number decreases with increasing κ for a fixed Peclet number and a given Reynolds number. It is also observed that the average Nusselt number is increasing as Peclet number increases for a fixed Re and a fixed κ.Item Mass transfer into a spherical bubble(2016-10-02) Saboni A.; Alexandrova S.; Karsheva M.; Gourdon C.A numerical study has been conducted to investigate the mass transfer inside a spherical bubble at low to moderate Reynolds numbers. The Navier-Stokes and diffusion-convection equations were solved numerically by a finite difference method. The effect of the bubble Schmidt number (over the range 0.1Item 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 MICROWAVE-ASSISTED SYNTHESIS OF SILVER NANOPARTICLES AS CATALYST FOR AIR GAS-DIFFUSION ELECTRODES(2022-01-01) Mladenova B.; Stankulov T.; Stankov S.; Boukoureshtlieva R.; Momchilov A.; Karsheva M.; Hinkov I.In this work, silver nanoparticles were synthesized from silver nitrate aqueous solution by using microwave irradiation. The morphology of the synthesized nanoparticles was studied by UV-Vis spectroscopy and by transmission electron microscopy showing spherical shapes with diameters of about 10 nm. The X-ray diffraction analysis exhibits their crystalline nature with face-centered cubic structure. Afterward, silver nanoparticles were integrated into activated carbon Norit NK to obtain catalytic composites. These composites were incorporated in the active layer of air gas-diffusion electrodes in order to study the catalytic activity for oxygen reduction reaction. For this purpose, a non-aggressive electrolyte solution of NaCl was used as an electrolyte. The obtained electrochemical results show a stable operation of all electrodes. Higher performance was found for composites containing 2 % wt. silver nanoparticles.Item Natural antioxidants from citrus mandarin peels. extraction of polyphenols; effect of operational conditions on total polyphenols contents and antioxidant activity(2013-05-22) Karsheva M.; Kirova E.; Alexandrova S.The main waste of the citrus fruits after processing is the citrus peel. The extraction of valuable components from mandarin peels with ethanol-in-water solutions was investigated. The effect of the operational conditions on the total extracted amount, the totalpolyphenols content and antioxidant activity was studied. The conditions varied were: theethanol concentration, the particle size and the temperature. Taking into account the thermolability of the polyphenols, vitamin C, etc., the influence of the drying temperature on the properties of extracts after re-dissolution was studied. It was found that the increase in drying temperature leads to decrease in TPPC in the extracts after re-dissolution. The worst results were obtained for drying temperature of 60°C - total polyphenols contents after drying and re-dissolution decreased almost twice (2.22 times). The comparison in TPPC and AOA of the mandarin peels' extracts with other citrus peels shows that the source studied is a perspective for possible use in food and cosmetic industries due to thevaluable components in it.Item Optimization and comparison of different techniques for extraction of flavonoids of Bulgarian Mavrud grape by-products(2019-01-01) Dimcheva V.; Karsheva M.In recent years, the interest in antioxidants in grape by-products has increased significantly as scientific research for the extraction and quantification of these compounds. In the present investigation was optimized the antioxidant yield of the grape pomace and seeds discharged as waste from the Bulgarian Mavrud winery, near to Trakiets village. There is a lack of information about extraction optimization and utilization of the selected grape by-products. The aim of the paper was studying the influence of some process parameters: effect of the degreasing pre-treatment of the material, effect of the extraction method and the extraction time on the yield of total flavonoid and anthocyanin contents and Trolox equivalent antioxidant capacity (TEAC). For this propose the extraction kinetics were obtained by using conventional and non-conventional extraction methods-magnetic stirring and ultrasound-assisted extraction (UAE) and using of degreased and non-degreased plant material. Degreasing was done by conventional Soxhlet extraction with n-hexane for an hour. All analyses were done using ultraviolet-visible (UV-vis) spectrophotometry. The results obtained show that the applied ultrasound power after the degreasing pre-treatment promoted optimal anthocyanin and flavonoid recovery for 180 minutes extraction time of both-grape pomace and seeds. The TEAC is not affected by applying UAE and degreasing pre-treatment technique. The optimization of the extraction conditions is important because it could alter an economic impact on the extraction evaluation of the Mavrud grape by-products. The grape pomace and seeds from Bulgarian Mavrud wine-making can be used to obtain secondary derivatives with high-added antioxidant value.Item Optimization of extraction of antioxidants from Bulgarian Mavrud by-Products(2018-01-01) Dimcheva V.; Karsheva M.; Diankov S.; Hinkov I.Grape pomace, an abundant by-product from the wine industry, is released in large quantities but remains unused. This investigation is focused on the optimization of extraction from grape pomace and grape seeds discharged as wastes from the Bulgarian Mavrud winery. The optimized parameters refer to the solid to the solvent ratio effect (1/10 g mL-1, 1/20 g mL-1, 1/30 g mL-1, 1/40 g mL-1, 1/50 g mL-1) and the solvent concentration (water or aqueous ethanol solutions) in relation on the total polyphenol, flavonoid and anthocyanin contents. The Trolox equivalent antioxidant capacity is also determined. All analyses are performed spectrophotometrically. All extraction runs are carried out at constant extractive parameters chosen previously - temperature, sample particle size, extraction manner. The optimal conditions are selected for the Mavrud seeds and pomace - 50 % ethanol in water solution, 1:20 g ml-1 solid to solvent ratio. The selection of the best extraction conditions is of great importance because it could alter the characteristics of the final extract having an economic impact on the extraction evaluation of the Bulgarian bio-Mavrud by-products.Item PHENOLIC COMPOUNDS IN PEELS, SEEDS, MARCS AND WINES FROM MAVRUD GRAPES(2020-01-01) Tochev D.; Karsheva M.; Pilev D.; Cayla L.; Masson G.; Mihaylova G.The aim of this work was to determine the amounts of different classes of phenolic compounds in ethanolic extracts from red grape marc and its components, peels and seeds, and to compare with wine musts, and red wine of the same variety of grapes. The results showed that the red grape marc was rich in polyphenolic compounds. Grape seeds demonstrated the highest contents of proanthocyanidines, (a type of flavonoid with high antioxidant activity).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.Item Plant mediated synthesis of silver nanoparticles using extracts from Tilia cordata, Matricaria chamomilla, Calendula officinalis and Lavandula angustifolia flowers(2018-01-01) Mladenova B.; Diankov S.; Karsheva M.; Stankov S.; Hinkov I.In this work, a simple, rapid and efficient green method for silver nanoparticles synthesis was developed by using extracts from four medicinal plants: flowers of Tilia cordata, Matricaria chamomilla, Calendula officinalis and Lavandula angustifolia, acting as reducing and capping agents. Silver nitrate was used as a precursor. The effect of the sunlight exposure and/or the sonication treatment on the synthesis process was investigated. The ultraviolet-visible spectroscopy (UV-Vis) studies showed surface Plasmon resonance peaks between 432 nm and 448 nm, characteristic of spherical silver nanoparticles. The morphology of the nanoparticles produced was investigated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The proposed method could be easily implemented for any kind of scientific or industrial application due to its cost effective nature.