Browsing by Author "Peshev D."
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Item Antibacterial activity of microencapsulated via spouted-bed hydro-alcoholic rosemary extracts(2020-01-01) Lazarova-Zdravkova N.; Terzieva T.; Peshev D.; Georgieva N.In this study the antibacterial activity of microencapsulated rosemary hydro-alcoholic extracts against Escherichia coli K12 was observed. The tested microcapsules were previously produced in five batches varying the type of the inert core and shell material as well as the content of fresh or concentrated rosemary extract. Batch 1 and batch 3 contained equal amount of non-concentrated rosemary extract where batch 2 and batch 4 consisted of the same amount of concentrated rosemary extract. Microcapsules from the last batch 5 were impregnated with three times higher quantity of the non-concentrated rosemary extract than the previous four batches. All five types of microcapsules were tested by the agar diffusion method and showed inhibitory effect against the bacterial strain. The highest antibacterial activity was obtained for batch 5 followed by the samples with concentrated extract (batch 2 and batch 4) and the least inhibitory effect was observed by the microcapsules with non-concentrated extract (batch 1 and batch 3).Item Antioxidant activity of membrane-fractionated coffee extracts in dependence of the storage conditions(2016-11-15) Mitev D.; Peshev D.; Peev G.; Peeva L.Present paper aims at one of the important aspects of the application of products with antioxidant activity: namely the preservation and change of their properties during the storage in different conditions, as well as their reliable characterisation. The tests of antioxidant properties were conducted with membrane-separated coffee extracts, isolated using a ``Microdyn Nadir NP030P`` type of commercial nanofiltration membrane (30% retention of NaCl; MWCO∼400). Prepared coffee permeates and retentates were stored 0/10 days in cool/warm conditions, with/without air access and at different illumination conditions. The kinetics of content changes was evaluated according to Folin-Ciocalteu method of total phenolic/reducing content determination.Item Antioxidant activity of membrane-fractionated coffee extracts in dependence of the storage conditions(2016-11-15) Mitev D.; Peshev D.; Peev G.; Peeva L.Present paper aims at one of the important aspects of the application of products with antioxidant activity: namely the preservation and change of their properties during the storage in different conditions, as well as their reliable characterisation. The tests of antioxidant properties were conducted with membrane-separated coffee extracts, isolated using a ``Microdyn Nadir NP030P`` type of commercial nanofiltration membrane (30% retention of NaCl; MWCO∼400). Prepared coffee permeates and retentates were stored 0/10 days in cool/warm conditions, with/without air access and at different illumination conditions. The kinetics of content changes was evaluated according to Folin-Ciocalteu method of total phenolic/reducing content determination.Item Depot effect of bioactive components in experimental membrane filtrations(2017-02-06) Mitev D.; Peshev D.; Peev G.; Peeva L.Depot effects were found to be accompanying phenomena of membrane separation processes. Accumulation of target species in the membrane matrix during feasibility tests can hamper proper conclusions or compromise the filtration results. Therefore, we investigated the effects of delayed membrane release of chlorogenic acid and caffeine, considered as key compounds of interest in spent coffee products' recovery treatment. Permeate fluxes and key components release were studied in course of 24 hours via nanofiltration of pure solvent, both immediately after the mock solution filtration and after idle stay. Conclusions are drawn and recommendations advised for proper analysis of experimental data on membrane screening.Item Depot effect of bioactive components in experimental membrane filtrations(2017-02-06) Mitev D.; Peshev D.; Peev G.; Peeva L.Depot effects were found to be accompanying phenomena of membrane separation processes. Accumulation of target species in the membrane matrix during feasibility tests can hamper proper conclusions or compromise the filtration results. Therefore, we investigated the effects of delayed membrane release of chlorogenic acid and caffeine, considered as key compounds of interest in spent coffee products' recovery treatment. Permeate fluxes and key components release were studied in course of 24 hours via nanofiltration of pure solvent, both immediately after the mock solution filtration and after idle stay. Conclusions are drawn and recommendations advised for proper analysis of experimental data on membrane screening.Item EFFECT OF STORAGE STABILITY ON THE ANTIMICROBIAL ACTIVITY OF MICROENCAPSULATED VIA SPOUTED-BED ROSEMARY EXTRACTS(2020-01-01) Lazarova-Zdravkova N.; Peshev D.; Georgieva N.Long-term stability of microencapsulated via spouted-bed rosemary hydro-alcoholic extracts was studied regarding their antibacterial activity. The samples were stored in dark place at 4°C for 10 months. Five batches with variation in the incorporated extracts and composition of the coating agent were tested by means of the agar diffusion method against two model strains, the Gram-negative Escherichia coli K12 and the Gram-positive Bacillus subtilis 356. Inhibitory effect was obtained from all five samples against the Gram-positive bacteria. None of the studied products showed activity against the Gram-negative strain. The most prominent effect against B. subtilis 356 was detected by microcapsules of batch 5 containing the highest amount of fresh rosemary extract, followed by the samples with concentrated extract (batch 2 and 4). The least inhibitory effect was observed by the microcapsules of batch 1 and 3, containing a lower quantity of fresh non-concentrated extractItem How to avoid concentration unsteadiness with a CVD precursor delivery system employing bubbler?(2016-11-15) Peev G.; Peshev D.An approach of great certainty is suggested as to avoid concentration unsteadiness with a CVD delivery system employing bubbler. Assuming that the carrier gas has to be saturated of precursor vapour during the entire CVD experiment a set of equations has been selected from the literature for calculating the height of liquid layer in the bubbler which is necessary to this aim. The selection is made on the prerequisites that gas bubbles are spherical, diffusion of precursor vapour in them is molecular and it takes place during their rising only, which has a velocity equal to the terminal bubble velocity of rising. The errors at levels lower than the one for saturation are discussed. Heights of Al(CH3)3 calculated using the approach are compared to those at which the bubbler controlling LED indicator of Dow Electronic Materials lights green, amber or red.Item How to avoid concentration unsteadiness with a CVD precursor delivery system employing bubbler?(2016-11-15) Peev G.; Peshev D.An approach of great certainty is suggested as to avoid concentration unsteadiness with a CVD delivery system employing bubbler. Assuming that the carrier gas has to be saturated of precursor vapour during the entire CVD experiment a set of equations has been selected from the literature for calculating the height of liquid layer in the bubbler which is necessary to this aim. The selection is made on the prerequisites that gas bubbles are spherical, diffusion of precursor vapour in them is molecular and it takes place during their rising only, which has a velocity equal to the terminal bubble velocity of rising. The errors at levels lower than the one for saturation are discussed. Heights of Al(CH3)3 calculated using the approach are compared to those at which the bubbler controlling LED indicator of Dow Electronic Materials lights green, amber or red.Item Multi-scale modelling of OSN batch concentration with spiral-wound membrane modules using OSN Designer(2016-05-01) Shi B.; Peshev D.; Marchetti P.; Zhang S.; Livingston A.G.Three commercial spiral-wound membrane modules of different sizes, from 1.8″ × 12″ to 4.0″ × 40″, are used to concentrate a solution of sucrose octaacetate in ethyl acetate under different operating conditions. A mathematical model to describe the batch concentration process is developed, based on a combination of the classical solution diffusion membrane transport model and the film theory, to account for the mass transfer effects. The model was implemented using the ``OSN Designer`` software tool. The membrane transport model parameters as well as all parameters in the pressure drop and mass transfer correlations for the spiral-wound modules were obtained from regression on a limited number of experimental data at steady state conditions. Excellent agreement was found between the experimental and multi-scale modelling performance data under various operating conditions. The results illustrate that the performance of a large scale batch concentration process with spiral-wound membrane modules can be predicted based on laboratory crossflow flat sheet test data when the fluid dynamics and mass transfer characteristics in the module, and the necessary channel geometry are known. In addition, the effects of concentration polarisation, pressure drop through feed and permeate channels, and thermodynamic non-ideality of the solution at large scale batch concentration are also investigated.Item PECVD polymerised coatings on thermo-sensitive plastic support(2016-02-09) Mitev D.; Radeva E.; Peshev D.; Cook M.; Peeva L.With this paper we describe several alternative approaches aimed at polymer-on- polymer coatings, produced by Plasma Enhanced Chemical Vapour Deposition (PECVD) technique. In our case three types of input compounds were applied for varied ``cold plasma`` PECVD deposition of nano-thick functional layers: namely hexamethyldisiloxane (HMDSO), pentane and toluene onto plastic substrates. The output characterisations through SEM imaging, ATR-FTIR, EDX, AFM and contact angle measurements, proved the methods' feasibility and properties of the plasma-polymerised coatings.Item Performance of spiral-wound membrane modules in organic solvent nanofiltration - Fluid dynamics and mass transfer characteristics(2015-11-05) Shi B.; Marchetti P.; Peshev D.; Zhang S.; Livingston A.G.During the past few decades organic solvent nanofiltration has received a great deal of attention and a growing number of studies has been reported on development and optimisation of solvent resistant membranes and their transport mechanism. However, most of these studies have used flat sheet membranes. On the other hand, many researchers studied fluid dynamics and mass transfer in spiral-wound membrane modules, almost exclusively in aqueous solutions. This paper reports the performance of four spiral-wound membrane modules tested in 0-20. wt% solutions of sucrose octaacetate in ethyl acetate under various pressures and retentate flowrates. These modules were made of two different types of membranes (a commercial membrane, PuraMem® S600, and a development product, Lab-1, from Evonik Membrane Extraction Technology Limited) and covered three module sizes (1.8″×12″, 2.5″×40″ and 4.0″×40″). All modules had the same feed and permeate spacers. The classical solution diffusion model was applied to describe the transport of solute and solvent through the membrane and regress the unknown model parameters from flat sheet data. Correlations for characterising the fluid dynamics and mass transfer in the spiral-wound membrane modules, as well as the parameters describing the feed and permeate channels, were determined by performing the regression of experimental data of a 1.8″×12″ PuraMem® S600 membrane module. The classical solution-diffusion model, combined with the film theory, was then successfully applied to predict the performance of other modules of larger size (such as the 2.5″×40″ and 4.0″×40″ module sizes) and/or made of a different membrane material (such as Lab-1). The procedure proposed in this paper predicts the performance of a specific module by obtaining a limited number of experimental data for flat sheets and a 1.8″×12″ spiral-wound membrane module only (necessary to obtain the fitting parameters characteristic of the membrane and the module). Furthermore, with this procedure, it is not necessary to know a priori the spacer geometry, because the necessary information about the spacer geometry will be also obtained by regression of few experimental data.Item Potential possibilities of a new method for yield stress determination(2016-01-01) Peev G.; Peshev D.; Nikolova A.One-D solution for the hydrodynamic characteristics of waveless film flow of an Ellis liquid on a horizontal rotating disk is obtained and considered for determination of the liquid yield stress. Several versions of the method based on the film thickness of the remaining liquid on the disk at a zero feed flow rate are proposed. Verification that such layer remains is provided. The limitations of the method advanced which refer to wave formation, film breakup, liquid adhesion and disk wetting are discussed in view of its application in rheometry.Item Removal of cadmium and copper ions by Trichosporon cutaneum R57 cells immobilized onto polyvinyl alcohol/tetraethoxysilane hybrid matrices(2010-06-16) Bryaskova R.; Georgieva N.; Peshev D.Polyvinyl alcohol (PVA) and tetraethoxysilane (TEOS) hybrid materials were prepared by sol-gel methods and tested as matrices for immobilization of Trichosporon cutaneum R57, capable of removing cadmium and copper ions from aqueous solutions. A kinetic model was applied and the effects of matrix TEOS content on the copper and cadmium uptake equilibria and rate constants were investigated. © 2010 Versita Warsaw and Springer-Verlag Wien.Item VALORIZATION OF WASTE LAVENDER RESIDUE FROM THE ESSENTIAL OIL INDUSTRY FOR PRODUCTION OF ROSMARINIC ACID -A STUDY ON THE SOLID-LIQUID EXTRACTION(2022-01-01) Chilev C.; Simeonov E.; Dimitrova B.; Yonkova V.; Pietsch S.; Heinrich S.; Peshev D.The possibility for valorization of the waste lavender residue from the essential oil industry via solvent extraction was studied. The plant residue of Lavandula angustifolia, from which the lavender oil is extracted through steam distillation, contains Key Biologically Active Components (KBAC) such as: rosmarinic acid, caffeic acid, luteolin. The feasibility of the solvent extraction for their isolation was assessed by comparison of the kinetics and equilibrium of extraction of KBAC from spent and raw plant material (collected from the same batch before the steam distillation) using different solvent compositions. The parameters of the extraction process were experimentally and numerically optimized. To determine the most efficient solvent, two pure and two mixed solvents were tested: pure water, 99.9 % ethanol and their mixtures - (40 % and 60 % ethanol). Using 40 % ethanol as extraction solvent resulted in maximum recovery of KBAC. A mathematical model for the solid-liquid extraction from lavender materials was developed. The values of the model parameters were determined using the Regular regime method. A four-parameter empirical model for prediction of the effective diffusivity, Deff, was also applied. The model adequacy was experimentally verified. Based on the theoretical and experimental results KBAC recovery the following extraction conditions were recommended: extraction time - 30 min, temperature - 30 °C, liquid-solid ratio - 0,01 m3 kg- and 40 % ethanol as an extraction solvent.