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61.
Solubility of carnosic acid and carnosol from rosemary extract in supercritical $CO_2$
Klavdija Rižnar, Štefan Čelan, Mojca Škerget, Željko Knez, 2008, original scientific article

Abstract: Rosemary leaves extract are known to have significant antioxidant properties and are widely used in foods and nutritional supplements. Compounds responsible for these antioxidant properties are mainly the phenolic diterpenes. The major phenolic diterpenes are carnosic acid and carnosol. Much interest has been focused on the isolation of carnosic acid, due to its wide spectrum of actions and beneficial effects on human health. In this work a natural rosemary extract, containing 73.9% carnosic acid and 14.7% carnosol, was investigated regarding the solubility of carnosic acid and carnosol in supercritical $CO_2$. The solubility measurements, using a static-analytic method, were performed at temperatures 40, 60 and 80 °C and at pressures ranging from 98 to 402 bar. The Chrastil model was used to correlate the obtained experimental solubility data.
Keywords: rožmarin, karnozolna kislina, topnost, karnozol, topnost
Published: 11.08.2015; Views: 1545; Downloads: 90
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62.
Industrijsko uporabni organski polimerni spektralno selektivni premazi za sončne toplotne zbiralnike
Miha Steinbücher, 2015, doctoral dissertation

Abstract: Sončna toplotna energija se v južni Evropi in Sredozemlju kaže kot najbolj sprejemljiv vir obnovljive energije. Za njeno množično uporabo je potrebno razviti visoko zmogljive, trajne in cenovno ugodne materiale. To delo obravnava organske polimerne premaze, namenjene sončnim toplotnim zbiralnikom, ki izpolnjujejo zgoraj naštete pogoje. Črne od debeline odvisno spektralno selektivne premaze (thickness sensitive spectrally selective (TSSS)) in od debeline neodvisno spektralno selektivne premaze (thickness insensitive spectrally selective (TISS)) smo zasnovali na tehnologiji silanskega oplaščenja anorganskih pigmentov. Razvili in optimizirali smo TSSS premaz, ki izpolnjuje vse zastavljene zahteve in ga je mogoče nanašati z uveljavljenimi industrijskimi metodami nanosa premazov. Njegovo trajnost je potrdil neodvisni zunanji laboratorij. Povezali smo površinske lastnosti utrjenega filma premaza z njegovo selektivnostjo in tako nadgradili predhodno vedenje o spektralno selektivnih premazih. Optimizirali smo črne in barvne TISS premaze. Pokazali smo povezavo med kemizmom poliola v poliuretanskih spektralno selektivnih premazih in njihovo selektivnostjo. V TISS premazih smo kot prvi uporabili organske pigmente za dosego višje barvne jakosti. Razvili smo fluoropolimerne TSSS premaze. Fluoropoliuretanski TSSS premazi so zaradi visoke selektivnosti in nižje temperaturne odpornosti primerni le za nišne aplikacije, kot so fasadni sončni toplotni sprejemniki. V te namene smo, spet kot prvi z uporabo organskih pigmentov v TSSS premazih, razvili visoko zmogljive modre premaze. Pokazali smo možnost razvoja termoplastičnih fluoropolimernih TSSS premazov. Z uporabo silansko oplaščenih črnih in organskih modrih pigmentov ter posledično optimizacijo faktorja polnjenja premaza smo razvili visoko zmogljive in trajne modre silikonpoliestrske TSSS premaze. Razviti premazi, ki so primerni za industrijsko uporabo, omogočajo izdelavo cenovno ugodnih, zmogljivih in trajnih sončnih toplotnih zbiralnikov. Znanje, pridobljeno pri njihovem razvoju, pa omogoča razlago predhodno neznanih ali nepojasnjenih lastnosti spektralno selektivnih premazov.
Keywords: Spektralna selektivnost, Premaz, Pigmenti, Veziva, Sončni toplotni zbiralnik, Toplotne tehnologije
Published: 15.07.2015; Views: 1472; Downloads: 184
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63.
Pressure stability of lipases and their use in different systems
Maja Leitgeb, Željko Knez, 2001, original scientific article

Abstract: For the investigation of the solvent impact on the enzymes, lipases from different sources (Pseudomonas fluorescences, Rhizopus javanicus, Rhizopus niveus, Candida rugose and Porcine pancreas) were used. Stability and activity of these lipases in aqueous medium in supercritical $CO_2$ and liquid propane at 100 bar and 40°C were studied. On the basis of previous results lipases were used for their application in two different systems. The application of the polysulphone membrane in the continuous stirred tank membrane reactor was studied on the model system of the hydrolysis of oleyl oleate in propane at high pressure. As a catalyst the Candida rugosa lipase was used. The next utilization of lipases was the use of on silica arerogel self-immobilized lipase from Porcine pancreas as catalyst for esterification reaction in near-critical propane at 40°C and 100 bar.
Keywords: chemical processing, supercritical fluids, lipases, enzyme stability, high pressure membrane reactor
Published: 10.07.2015; Views: 824; Downloads: 114
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64.
Extraction of lutein diesters from tagetes erecta using supercritical $CO_2$ and liquid propane
Mojca Škerget, Miran Bezjak, Katja Makovšek, Željko Knez, 2010, original scientific article

Abstract: The efficiency of high pressure extraction of lutein diesters from marigold (Tagetes erecta) flower petals has been investigated. The solvents used for extraction were supercritical carbon dioxide and liquid propane. Operating parameters were 300 bar and 40, 60 and 80 °C for $CO_2$ and 100, 150, 200 bar and 40 and 60 °C for propane, respectively. The influence of process parameterson the total yield of extraction and content of lutein diesters in the extracts was investigated. The results show, that solvent power of propanefor lutein diesters is approximately 3.5 times higher than of $CO_2$. The calculation procedure based on the Fick's second law was applied to determine the diffusivities of lutein diesters during extraction from marigold flower petals for both extraction stages: a constant rate stage followed by a stage of decreasing rate. The mathematical model based on the Fick's second law well described the experimental extraction results.
Keywords: lutein diesters, Tagetes errecta, extraction, supercritical $CO_2$, subcritical propane
Published: 10.07.2015; Views: 836; Downloads: 53
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65.
Enzymatic esterification of glycerol and stearic acid in non-conventional media
Zsófia Csanádi, Katalin Bélafi-Bakó, Eszter Szentgyörgyi, László Gubicza, Željko Knez, Maja Leitgeb, 2010, original scientific article

Abstract: Ionic liquids as trihexyl-tetradecyl-phophonium-dicyanamide (Cyphos 105) and cocosalkyl-pentaethoxi-methyl-ammonium-methosulfate (Ammoeng 100) were applied for the esterification of stearic acid and glycerol using Candida antarctica lipase (Novozyme 435). When only ILs were applied as solvents at 1:15 initial substrate molar ratio the conversion was 76 and 78 % in the case of two kinds of ILs, respectively. Mixed the ILs and supercritical $CO_2$ the conversion reached 79 and 86 %. The conversion was found highest in supercritical $CO_2$, reached 90 %. Moreover formation of glycerol-di-stearate is much lower in the case of ILs comparing with $SCCO_2$.
Keywords: glycerol-mono-stearate, Lipase, ionic liquids, supercritical $CO_2$, carbon dioxide
Published: 10.07.2015; Views: 703; Downloads: 83
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66.
Water sorption characteristics of a new type of gelatine powder, produced by a new high-pressure micronisation process
Christian Reibe, Željko Knez, 2010, original scientific article

Abstract: A new high-pressure micronisation process for Gelatine has been developed. By applying this process to gelatine, a new type of Gelatine was produced: Dry and pure Gelatine powder of high molecular mass. This powder was investigated,regarding its sorption behaviour and compared to its feedstock material. The feedstock Gelatine was of type B 200 Bloom, 6 mesh, having a molecular mass of 150,000 g $mol^{-1}$. The produced Gelatine powder's molecular mass was around 130,000 g $mol^{-1}$, while its mean particle size was 300 μm. Their sorption isotherms were investigated at 30 °C, 40 °C and 60 °C and water activities in the range from 0.055 to 0.836. At given water activities the Equilibrium Moisture Contents (EMC) decreases with increasing temperature.The measured sorption isotherms were fit with the Brunauer- Emmet-Teller (BET)- model and the Guggenheim- Anderson- deBoer (GAB)- model. Both models described the adsorption behaviour well in their range of validity, while only the GAB-model was adequate for describing the desorption behaviour. Hysteresis effect occurred in each adsorption-desorption pair. The isosteric heat of sorption of both substances was determined for adsorption, desorption respectively. Slight differences in the sorption behaviour occurred due to processing, while quality of the gelatine was not affected.
Keywords: $CO_2$ spray drying, gelatine powder, sorption isotherms, isosteric heat of sorption, Guggenheim-Anderson-deBoer model, Brunauer-Emmet-Teller model
Published: 10.07.2015; Views: 967; Downloads: 29
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67.
Potential of phenolic antioxidants
Iva Ružić, Mojca Škerget, Željko Knez, 2010, review article

Abstract: In vitro studies have shown a link between the consumption of food rich in (poly)phenols, especially flavonoids, and reduced risk of coronary heart diseases. Several flavonoids have been reported to prevent low density lipoprotein cholesterol oxidation in vitro. The aim of our work was to determine antioxidant and radical scavenging activity of flavonoids myricetin,quercetin, rutin, luteolin, apigenin, kaempferol, catechin, epicatechin and epigallocatechin gallate and to study the influence of chemical structure and flavonoid interactions on the ability to inhibit oxidation and scavenge free radicals. Two in vitro methods, i.e. oxidation of â-carotene in an emulsion system and DPPH (1,1-Diphenyl-2-picrylhydrazyl) radical scavenging assay, were applied. In addition, a review of in vivo studies that investigate the effectiveness of food flavonoids in reducing oxidative damage in human body was done and their results were analyzed and compared to in vitro results obtained in our laboratory. Although all tested flavonoids except apigenin showed strong antioxidant and antiradical properties in vitro, these findings can not be completely confirmed from the reviewed in vivo human studies since those results are sometimes contradictoryand inconsistent.
Keywords: phenolics, flavonoids, antioxidant activity, antiradical activity
Published: 10.07.2015; Views: 731; Downloads: 44
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68.
Subcritical water - a perspective reaction media for biomass processing to chemicals
Irena Pavlovič, Željko Knez, Mojca Škerget, 2013, published scientific conference contribution

Abstract: Biomass and water are recognized as a key renewable feedstock in sustainable production of chemicals, fuels and energy. Subcritical water (SubCW), or commonly referred as hot compressed water (HCW), is the water above boiling and below critical point (CP; 374 °C, 22.1 MPa). It has gained great attentionin the last few decades as a green, cheap, and nontoxic reagent for conversion of biomass into valuable chemicals. In this paper, hydrothermal reactions of cellulose, as the model biomass substance, with subcritical waterat mild temperature and pressure regimes have been studied. The experiments were done in a batch reactor in the temperature range of 220 ° - 300 °C. The main products distributed in liquid, gaseous and solid phase were separated and quantified. The conversions to each group of products were foundstrongly dependent on the temperature and residence time.
Keywords: celuloza, biomasa, subkritična voda, hidrotermana konverzija, bioolja
Published: 10.07.2015; Views: 792; Downloads: 56
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69.
Influence of process parameters on the extraction of flavanones from mandarin peel
Katja Makovšek, Željko Knez, Mojca Škerget, 2012, original scientific article

Abstract: Flavanones are an important group of flavonoids that are characteristic for citrus. In the present work isolation of flavanones from mandarin peel was performed by conventional extraction using water, ethanol, acetone and aqueous solutions of acetone and ethanol. The extracts were analysed on the content and composition of flavanones. Furthermore the DPPH radical scavenging activity of extracts was determined. Finally, the influence of extraction parameters (particle size, extraction temperature, extraction time,material to solvent ratio, number of extraction stages and type of solvent) on the yield and the efficiency of extraction were determined by Plackett-Burman experimental design. The results showed that 70% aqueous solution of acetone was the most efficient solvent for isolation of flavanones from mandarin peel. The main flavanones present in the obtained extracts were hesperidin (HES) and narirutin (NRT). The number of extraction stages influenced the yield of extraction, type of solvent influenced the hesperidin extraction efficiency and particle size of material influenced the narirutin extraction efficiency.
Keywords: conventional extraction, mandarin peel, flavanone, hesperidin, narirutin, Plackett-Bauman experimental design
Published: 10.07.2015; Views: 955; Downloads: 41
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70.
Biocompatible nanomaterials
Maja Leitgeb, Mateja Primožič, Željko Knez, 2012, independent scientific component part or a chapter in a monograph

Abstract: Nanotechnology represents an area holding significant promise for health care and biotechnology for many years to come. Nanomaterials are an emerging familyof novel materials that could be designed for specific properties. Thesematerials will probably bring about significant shifts in the manner we design, develop, and use materials. With the emergence of novel fabrication and characterization technologies, new combinations of nanomaterials or nanocomposites are beginning to be synthesized and characterized. They have potential for various biomedical applications; including magnetic resonance imaging (MRI) contrast enhancement, targeted drug delivery, hyperthermia, biological separation, protein immobilization, biosensors, etc. The use of magnetic carriers for efficient transport of various biomolecules (e.g. antibody, enzyme) has increased drastically in the recent years, especially inthe field of nanomedicine, where the bioactive molecule immobilized onto thesurface of a magnetic carrier acts a potential bioactive substance or drug to be transported and effectively released in the specific location. In this direction, superparamagnetic iron oxide nanoparticles (SPIONs) with appropriate surface chemistry have been widely used experimentally for numerous applications. In past decades, many carriers have been developed and investigated extensively, but mostly the group of chemically modified inorganic nanoparticles have showed low toxicity and generally possess versatile properties suitable for cellular delivery, including wide availability, rich functionality, good biocompatibility, potential capability of targeted delivery and controlled released of carried drugs. Because surfacechemistry greatly influences magnetic nanoparticles (MNPs) fate in the biological system, including the mechanisms of their cell recognition, biodistribution and immunes response it presents a specific focus for advancing engineering strategies to minimize potential nanotoxicity. Surface functionalization, a controlled process of chemical attachment of functional groups to the surface, is now integral to magnetic nanoparticle designs. Moreover, surface chemistry is essential to target the nanoparticles to specific sites. Several groups of coating materials are generally used to modify magnetic nanoparticle surface chemistry. Additionally, one of the most attractive routes for the surface modification of nanoparticles is using an organosilane. The biocompatibility of most nanoparticles could be greatly enhanced by introducing various synthetic polymers to their surface, thus, promoting better water solubility of the magnetic carrier. Silica is also one of the most frequently functional coatings used so far, as it has inherently superior functionalization capabilities, respectively. For these reasons, overthe last decade, nanomaterials have been highlighted as promising candidates for improving traditional materials.
Keywords: nanaomateriali, sinteza, aplikacije, karakterizacija
Published: 10.07.2015; Views: 47224; Downloads: 27
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