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1.
The development of a new process for gentle drying, micronisation and formulation of a high viscous biopoymer
Christian Reibe, 2011, doktorska disertacija

Opis: Biopolymers are characterised by their biodegradable behaviour in certain environments. Especially the development of natural biopolymers from renewable resources is gathering increasing interest in the scientific as well as in the industrial sectors . Since Biopolymers may be tailored to specific requirements, the encapsulation of pharmaceutical compounds or flavours in biopolymers would open wide avenues for the production of controlled- release systems. Most common mechanical pulverisation processes are milling and grinding. With these processes it is not possible to produce specific morphologies like foams or hollow spheres, but always splintered edges. Encapsulation is carried out by common precipitation techniques. Gelatine, as a widely applied biopolymer, represents one example of those substances of large interest, but it is difficult to process. Especially gelatines with high molecular mass are difficult or almost impossible to be pulverized by spray drying techniques, due to their high viscosity. In the frame of this research work, an integrated high-pressure spraying, drying and pulverization process for high viscous gelatine was developed, based on a combination of the water removing effects "Evaporation" and "Gas-solubility". The resulting products were dry, free-flowing gelatine powders, still exhibiting high molecular masses. Due to the new, gentle method of processing, a completely new gelatine product with unique properties was obtained. Even the encapsulation of edible oil in high ratios was found to be possible with this new process. The characterisation was carried out by standard methods for gelatine on the one hand side, and standard procedures for characterising powders on the other hand side. The developed process was patented under the identifier "WO 002009135601 A1".
Ključne besede: High Pressure Process, Supercritical Fluids, High molecular mass Gelatine, Micronisation, CO-2 - spray drying, Encapsulation, Gelatine Powder
Objavljeno: 26.01.2011; Ogledov: 2427; Prenosov: 68
.pdf Celotno besedilo (24,89 MB)

2.
Preparation of WO[sub]3 aerogel catalysts using supercritical CO[sub]2
Zoran Novak, Petra Kotnik, Željko Knez, 2004, izvirni znanstveni članek

Opis: Single tungsten oxide aerogels (WO3), binary oxide aerogels (WO3-Al2O3) and ternary oxide aerogels (WO3-SiO2-Al2O3) were prepared using standard sol-gel route. Tungsten oxide tetraethoxide (WO(OCH2CH3)4) was used as the sol-gel precursor. The excellent properties of the gels obtained by the sol-gel synthesis were preserved upon supercritical drying with CO2. After supercritical drying at 40 °C and 100 bar, all aerogels were calcined to 800 °C. The influence of the synthesis parameters on the catalytic activity of WO3as supported on silica andžor alumina aerogels was investigated through thetransformation of N-(phosphonomethyl)iminodiacetic acid to N-(phosphonomethyl)glycine. Despite including WO3 into single and mixed silicaand alumina aerogels, high specific surface areas (284-653 m2 g-1) were preserved. Higher conversion was obtained for catalysts with higher ratios of WO3 in the mixed silica-alumina aerogels that were calcined at 800 °C.
Ključne besede: chemical processing, aerogels, catalysts, tungsten oxides, preparation of aerogels, characterisation of aerogels, supercritical CO2, supercritical drying, high pressure technology
Objavljeno: 01.06.2012; Ogledov: 1087; Prenosov: 19
URL Povezava na celotno besedilo

3.
Silica aerogels as support for lipase catalyzed esterifications at sub- and supercritical conditions
Zoran Novak, Maja Leitgeb, Vlasta Krmelj, Željko Knez, 2003, izvirni znanstveni članek

Opis: The enzymes (lipases from Candida rugosa and porcine pancreas) were immobilized on silica aerogels by sol-gel procedure followed by supercritical drying with CO2. Such immobilized enzymes were used as biocatalysts for esterification in supercritical CO2 and near critical propane at 40 °C and 100 bar. It was found out that the initial reaction rates in propane rose two to three times in comparison with the same reaction, catalyzed by free lipase. SC CO2 deactivated the non-immobilized lipase in reaction mixture while with the immobilized enzyme the conversion was 35%. The initial reaction rates in propane were 20 times higher than in water medium due to the properties of propane as a medium for esterification of fatty acids.
Ključne besede: chemical processing, biotechnology, esterification, immobilization of enzymes, supercritial CO2, propane, lipases, supercritical CO2 drying
Objavljeno: 01.06.2012; Ogledov: 997; Prenosov: 10
URL Povezava na celotno besedilo

4.
5.
Water sorption characteristics of a new type of gelatine powder, produced by a new high-pressure micronisation process
Christian Reibe, Željko Knez, 2010, izvirni znanstveni članek

Opis: 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.
Ključne besede: $CO_2$ spray drying, gelatine powder, sorption isotherms, isosteric heat of sorption, Guggenheim-Anderson-deBoer model, Brunauer-Emmet-Teller model
Objavljeno: 10.07.2015; Ogledov: 567; Prenosov: 11
.pdf Celotno besedilo (317,43 KB)
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6.
Effect of drying parameters on physiochemical and sensory properties of fruit powders processed by PGSS-, vacuum- and spray-drying
Urban Feguš, Uroš Žigon, Marcus Petermann, Željko Knez, 2015, izvirni znanstveni članek

Opis: Aim of this experimental work was to investigate the possibility of producing fruit powders without employing drying aid and to investigate the effect of drying temperature on the final powder characteristics. Raw fruit materials (banana puree, strawberry puree and blueberry concentrate) were processed using three different drying techniques each opera- ting at different temperature conditions: vacuum-drying (–27–17 °C), spray-drying (130–160 °C) and PGSS-drying (112–152 °C). Moisture content, total colour difference, antioxidant activity and sensory characteristics of the proces- sed fruit powders were analysed. The results obtained from the experimental work indicate that investigated fruit pow- ders without or with minimal addition of maltodextrin can be produced. Additionally, it was observed that an increase in process temperature results in a higher loss of colour, reduced antioxidant activity and intensity of the flavour profile.
Ključne besede: particles from gas saturated solutions drying, vacuum-drying, spray-drying, sensory evaluation, fruit powders
Objavljeno: 18.08.2017; Ogledov: 257; Prenosov: 105
.pdf Celotno besedilo (249,24 KB)
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7.
Formation, characterization and application of polysaccharide aerogels
Gabrijela Horvat, 2018, doktorska disertacija

Opis: The aim of this PhD dissertation was to describe and analyze the preparation and characterization of polysaccharide aerogels and their future pharmaceutical and medical application. For the research, we used four types of polysaccharides: pectin, alginate, xanthan and guar. We used two types of pectin, high-methoxyl and low-methoxyl pectin, because of their different gelation mechanisms. The first part of the dissertation describes the preparation and characterization of pure polysaccharide aerogels. First, we prepared pectin spherical aerogels, cross-linked with three different ions, and we investigated their final properties. Later, we developed a new method for the preparation of alginate, pectin, xanthan and guar aerogels. We used only ethanol and no other cross-linkers. Ethanol was removed in the later processes of supercritical drying, and the remaining final material was thus only porous polysaccharide. By this method, we were able to prepare pure xanthan and guar aerogels. Prior to this study, xanthan and guar aerogels were prepared only as composites. Pectin aerogels prepared by the new method have amazing properties. On the other hand, alginate aerogels show poor characteristics, and thus the methods need to be optimised. We tried different alginate viscosities, different alcohols (methanol, ethanol, 1-propanol and 1-butanol), and we investigated longer (24h) and shorter (1h) gel setting times. The second part of this dissertation describes the pharmaceutical and medical applications of prepared aerogels. The release of diclofenac sodium from spherical pectin aerogels was investigated in vitro. Calcium cross-linked aerogels were not able to retain the drug, and its release was immediate. In order to achieve controlled release of diclofenac sodium, zinc ions had to be used as cross-linkers. Later, a low water-soluble drug, nifedipine, was used as a model drug for the monolithic aerogels prepared by the new method. The release of nifedipine from pectin and alginate aerogels was highly increased, compared to the crystalline drug. This result is promising for future evaluation of these materials for increasing the bioavailability of poorly water-soluble drugs. Nifedipine release from xanthan and guar aerogels was prolonged up to two weeks. This result reveals a new perspective on such materials for their potential use in medicine as implants and local drug delivery. According to these results, we then developed a new coating material for medical-grade stainless steel from xanthan and pectin. An aerogel coating was loaded with diclofenac sodium and indomethacin, and their release profiles were investigated in vitro. Electrochemical analysis and cell tests proved the safety of such materials for use in medicine. Using aerogel coatings, the drug can be introduced locally into the body; therefore, the need for intravenous, post-operational treatment is greatly reduced.
Ključne besede: polysaccharides, aerogels, supercritical drying, drug carriers
Objavljeno: 09.04.2018; Ogledov: 409; Prenosov: 88
.pdf Celotno besedilo (5,84 MB)

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