Opis: The study of two different methods of obtaining chiral alcohols is proposed herein.
The requirement of the relatively new paradigm of green chemistry associated with clean
technologies such as biocatalysis or non-conventional solvents, dense gases, was
focused at. Indeed, the two methods of production of chiral alcohols were:
- the conversion of acetophenone into (R)-1-phenylethanol in dense gases
catalysed by Lactobacillus brevis alcohol dehydrogenase and its
- the resolution of (±)-trans-1,2-cyclohexanediol by cocrystal formation with
tartaric acid followed by supercritical extraction.
In both cases high enantiopurities were achieved (ee>99%).Najdeno v: ključnih besedahPovzetek najdenega: ...cocrystal formation with
tartaric acid followed by supercritical extraction.
In both cases high enantiopurities were achieved (ee>99%)....Ključne besede: High-pressure technologies, enantiomers, green chemistry, R-1-phenylethanol, Lactobacillus brevis, alcohol dehydrogenase, NADP, liquid propane, enzyme deactivation, resolution, trans-1, 2-cyclohexanediol, tartaric acid, cocrystal, supercritical carbon dioxide, extraction, X-ray diffraction, differential scanning calorimetryObjavljeno: 02.02.2011; Ogledov: 928; Prenosov: 20 Polno besedilo (6,25 MB)
Opis: An Al86Mn3Be11 alloy cast into copper mould was subjected to metallographic investigation. The as-cast microstructure consisted of a quasicrystalline icosahedral phase (i-phase), Be4AlMn phase and, occasionally, a hexagonal phase. Al-rich solid solution represented the dominant phase. The chemical compositions of phases were determined using AES. The composition of the Be4AlMn slightly deviated from the stoichiometric composition, whereas the composition of the i-phase was approximately Al52Mn18Be30, containing an appreciable amount of Be. The average composition of the hexagonal phase was Al66Mn21Be13. Deep etching and particle extraction provided a deep insight into the three-dimensional morphology of the i-phase and the hexagonal phase, whereas Be4AlMn was slightly attacked by the etchant. The i-phase was present predominantly in the form of dendrites and a rodlike eutectic phase. The hexagonal phase was primarily in the form of hexagonal platelets, whereas Be4AlMn was rather irregular in shape. The morphology of the i-phase can be explained by predominant growth in 3-fold directions and the lowest energy of the 5-fold planes, leading to the faceting and adopting a pentagonal dodecahedron shape. The brightnesses of phases in the backscattered electron images were rationalized by determining their backscattering coefficients. TEM investigation showed considerable phason strain in the i-phase, and the polycrystalline nature of the Be4AlMn phase.Najdeno v: ključnih besedahPovzetek najdenega: ...phase was Al66Mn21Be13. Deep etching and particle extraction provided a deep insight into the three-dimensional...Ključne besede: aluminium alloys, deep etching, metallography, particle extraction, quasicrystalObjavljeno: 31.05.2012; Ogledov: 185; Prenosov: 0 Polno besedilo (0,00 KB)
Opis: Grapes and wine production residuals, containing grape skins, seeds and stems, represent important sources of phenolic compounds. Red wines are rich in phenolic antioxidants while white wines generally show lower (poly)phenolic content and antioxidant activity. The main difference in the production of white and red wines is the fermentation step. The fermentation of red grapes includes maceration, i.e. it takes place in both liquid and solid parts of the grape. In the case of white wines, the must is clarified before the fermentation starts, cultured yeasts are added to convert the must to wine and antioxidant sulfur dioxide is inserted to protect the wine.
The objective of the PhD research was to study antioxidant potential of white grape phenolics both in raw material and fermentation products. First, the standards of phenolic compounds commonly found in white grapes and wines were tested for their antioxidant and antiradical activity. All tested compounds except apigenin showed strong antioxidant and antiradical properties. Afterwards, conventional solid-liquid extraction (CE) and pressurized liquid extraction (PLE) of phenolic compounds from grape seeds were performed. The optimal extraction conditions were investigated and extracts were analyzed in order to determine their total phenolic content, individual phenolic compounds and antiradical potential. Two different drying methods (hot air and freeze drying) were applied to the seeds. Solvent efficiencies of water, ethanol and water-ethanol mixtures were compared at different temperatures. In addition, supercritical fluid extraction (SFE) with CO2 was investigated as the technique for the recovery of phenolic compounds and for the pretreatment of white grape seed samples. Both CE and PLE gave extracts rich in phenolic compounds with good antiradical properties and, generally, the best results were obtained with PLE at 130°C. At the end, the influence of maceration process on the content and the activity of grape phenolic antioxidants in white wines was studied. For such a purpose, six commercially available macerated white wines from Italy and Croatia were analyzed. In addition, eight non-macerated wines from the same region and variety were studied and compared to macerated wines. The experiments have shown that the maceration process increases the total phenolic content and antiradical activity of the wine. It enables the production of white wines rich in phenolic compounds and with strong antiradical properties in completely natural way using only the grapes and without addition of any chemical agents. Najdeno v: ključnih besedahPovzetek najdenega: ...antioxidant and antiradical properties. Afterwards, conventional solid-liquid extraction (CE) and pressurized liquid extraction (PLE) of...Ključne besede: white grapes, white wine, maceration, antioxidant activity, polyphenols, extraction, PLE, SFE.Objavljeno: 05.04.2012; Ogledov: 614; Prenosov: 36 Polno besedilo (5,65 MB)
Najdeno v: ključnih besedahPovzetek najdenega: ...chemical processing, high pressure technology, extraction, CO2, natural antioxidants, rosemary extract, food additives...Ključne besede: chemical processing, high pressure technology, extraction, CO2, natural antioxidants, rosemary extract, food additivesObjavljeno: 31.05.2012; Ogledov: 174; Prenosov: 4 Polno besedilo (0,00 KB)
Opis: In the present work, high-pressure extraction of borage (Borago officinalis L.) and evening primrose (Oenothera biennis L.) seed oil, containing the valuable -linolenic acid (GLA), has been investigated. Extraction was performed with supercritical carbon dioxide on a semi-continuous flow apparatus at pressures of 200 and 300 bar, and at temperatures of 40 and 60 °C. A constant flow rate of carbon dioxide in the range from 0.17 to 0.20 kgžhwas maintained during extraction. The extraction yields obtained using dense CO2 were similar to those obtained with conventional extraction using hexane as solvent. The composition of extracted crude oil was determined by GCanalysis. The best results were obtained at 300 bar and 40 °C for both seed types extracted, where the quality of oil was highest with regard to GLA content. The evening primrose seed oil extracted with supercritical fluid extraction was particularly rich in unsaturated fatty acidsČ up to 89.7 wt-% of total free fatty acids in the oil. The dynamic behavior of the extraction runs was analyzed using two mathematical models for describing the constant rate period and the subsequent falling rate period. Based on the experimental data, external mass transfer coefficients, diffusion coefficients and diffusivity in solid phase were estimated. Results showed good agreement between calculated and experimental data.Najdeno v: ključnih besedahKljučne besede: chemical processing, high pressure technology, supecritical CO2, seed oil extraction, evening primrose, borage, free fatty acids, kinetics, modelingObjavljeno: 31.05.2012; Ogledov: 203; Prenosov: 2 Polno besedilo (0,00 KB)
Opis: The effect of different extraction set-ups that influence the extraction efficiency of catechins and caffeine from green tea leaves (variety Fanning Belas, China) were studied using different aqueous and pure solvents (acetone,ethanol, methanol, acetonitrile, water), different temperatures (60, 80, 95 and 100 °C) and times (5-240 min). Raw extracts were analysed for contents of major catechins (EC, EGC, ECG, EGCG), caffeine, proanthocyanidins and flavonols (myricetin, caempherol, quercetin). Starting material was found to contain 191 g major catechins/kg material, 36 g caffeinežkg material and 5.2 g flavonols/kg material on a dry mass basis. The content of major catechins in green tea extracts varied from approximately 280-580 g/kg dry extract, with extraction efficiencies of major catechins varying from 61% to almost 100%. Content of caffeine in extract was in the range of 75 g/kg, where its extraction efficiency varied from 62% to 76%. Average extraction yield was 30% with exceptions when using pure acetone and acetonitrile, where extraction yield was about 3%. Contents of flavonols and proanthocyanidins were in the ranges 6-20 and 12-19 g/kg, respectively. Different extraction procedures with water were also investigated and optimal conditions determined: maximum achieved extraction efficiency of catechins with water wasobtained at 80 °C after 20 min (97%) and at 95 °C after 10 min of extraction (90%). Degradation of catechins was observed at higher extraction temperatures and with prolonged extraction times. Using a lower ratio of solvent to material, extraction efficiencies were increased by applying a multi-step extraction procedure. Optimal extraction procedure was then performed using decaffeinated green tea leaves, which were obtained by high-pressure extraction with CO2, when 98% of caffeine was selectively isolated without significant impact on valuable catechins.Najdeno v: ključnih besedahKljučne besede: chemical processing, extraction, green tea, catechins, caffein, decaffeinated green tea extract, raw green tea extractObjavljeno: 30.05.2012; Ogledov: 215; Prenosov: 4 Polno besedilo (0,00 KB)
Opis: This study was aimed to assess the feasibility of extracting chlorophylls fromstinging nettle (Urtica dioica L.) by solvent extraction. In preliminary, the investigation concerned three parts of raw material (leaves, stalk and whole plant), different preservation techniques (blanching and drying) and different storage temperatures of preserved material ( |20 C for blanched and 4 C for dried sample). Extracts were analysed for chlorophyll A and chlorophyll B, respectively, by means of HPLC method. Afterwards, optimizationof single-step conventional extraction was carried out by examining the influence of the following process parameters on the extraction yield and isolation efficiency of chlorophylls: type of organic solvent, content of water in ethanol/water mixtures, ratio solvent/material, temperature, time of extraction and pH of the extraction mixture. Furthermore,to improve the yield and/or the selectivity of the extraction, multi-step conventional extraction experiments as well as other solid ]liquid extraction techniques (soxhlet and ultra-sound assisted) were performed and compared. c 2007 Elsevier B.V. All rights reserved.Najdeno v: ključnih besedahPovzetek najdenega: ...fromstinging nettle (Urtica dioica L.) by solvent extraction. In preliminary, the investigation concerned three parts...Ključne besede: chemical processing, extraction, nettle, isolation of chlorophyll, chlorophyll content, solvent extractionObjavljeno: 31.05.2012; Ogledov: 187; Prenosov: 2 Polno besedilo (0,00 KB)
Opis: Supercritical fluid extraction of chamomile flower heads was performed on semicontinuous extraction apparatus in the lab scale using carbon dioxide as solvent. The results of high pressure experiments were compared with those obtained with Soxhlet extraction, steam distillation and maceration. The obtained extracts were analysed by HPLC on ?-bisabolol, matricine and chamazulene content and by gravimetrical method on essential oil and waxes content. The highest content of active components in extracts and highest extraction yield were obtained using SFE at 250 bar and 40 °C. At this extraction conditions the two step separation was used to optimize the separation of essential oil from unwanted components. Dynamic behaviour of theSFE with single step separation runs were analysed using two mathematical models for describing the constant rate period and subsequent falling rate period. Based on the experimental data, external mass transfer coefficient, diffusion coefficient and diffusivity in solid phase were estimated. Results showed acceptable agreement of calculated and experimental data. Based on theparameters determined in the lab scale, the extraction process was successfully transferred to pilot scale.Najdeno v: ključnih besedahKljučne besede: chemical processing, high pressure technology, supercritical extraction, chamomile, matricine, chamazulen, scale-upObjavljeno: 31.05.2012; Ogledov: 127; Prenosov: 0 Polno besedilo (0,00 KB)
Opis: Pure copper (99.99), prepared in the sample of square cross-section (10 x 10 mm2) and length about 50 mm, was extremely plastically deformed with the repeated application of Equal Channel Angular Pressing (ECAP). ECAP was applied as an effective technique for producing bulk nano-scaled structures. Optical properties of the sample were investigated using Raman spectroscopy. Two types of lines: narrow (with width of 7 cm¡1) and wide ( 40 cm¡1) are registered. Existence of two types of lines indicates that in the specimen exists nano-sized crystal structures of both Cu and CuO related with three dimensional amorphous boundary spaces, which indicates that plastic deformation of the sample did not lead to total amorphisation of the specimen.Najdeno v: ključnih besedahPovzetek najdenega: ...plastically deformed copper, hydrometallurgical extraction of metals...Ključne besede: plastically deformed copper, hydrometallurgical extraction of metalsObjavljeno: 31.05.2012; Ogledov: 131; Prenosov: 2 Polno besedilo (0,00 KB)
Opis: The interest in natural food colorants shows an increasing tendency due to the strictening rules and consumersć concerns over synthetic additives. One of natural pigments with high potential are anthocyanins, which are providing colours from yellow to blue in berries, flowers and vegetables. However the use of anthocyanins as food colorants is still limited because of their relatively low stability during processing, formulation and storage. In this work extraction of anthocyanins from grape marc was investigated with different concentrations of acetone (50 wt%, 70 wt% and 100 wt%) at 20 °C and at 60 °C temperatures. Pilot-scale extraction of grape marc was performed upon the results obtained from laboratory scale experiments. High-pressure concentrated powder form (CPF) technique was applied in order to formulate the obtained extracts in powderous form. Carrier materials, such as starch and silica were tested. Colorimetric properties (lightness, chroma and hue angle) of powderous products were measured and compared with synthetic colorants. Colour stability was monitored during storage at different conditions (light/dark and ambient temperature/refrigerator). The results were compared with the non-formulated extracts, which were stored at same conditions. Product formulation with CPF improved the colour stability of anthocyanin extracts, while for the non-formulated extracts degradation of colour rapidly occurred. The results show that formulated anthocyanin extracts have potential use as natural colorants. However, the major difference compared to synthetic colorants is still in the saturation of the colour.Najdeno v: ključnih besedahKljučne besede: chemical processing, extraction, stabilization, anthocyanins, grape marc, formulation, concentrated powder formObjavljeno: 31.05.2012; Ogledov: 178; Prenosov: 1 Polno besedilo (0,00 KB)