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1.
2.
Properties of Mint as a Food Preservative
Rok Penko, 2011, diplomsko delo

Opis: This study was designed to evaluate antimicrobial and antioxidant activities of the mint extracts from Mentha piperita L. and Mentha aquatica L. In vitro antibacterial activity against two foodborne bacteria (Listeria monocytogenes, Staphylococcus aureus) was evaluated by the well diffusion method. The activity was assessed by the diameter of the inhibition zone. Four of the five extracts from Mentha piperita were active against S. aureus, but none of the extracts was active against L. monocytogenes. Extracts obtained from Mentha aquatica showed no activity against both foodborne bacteria. The horseradish peroxidase/guaiacol assay was used to investigate in vitro antioxidant activity of two mint extracts (Mentha piperita and Mentha aquatica). The ascorbic acid was tested as a reference compound with known antioxidant activity to validate our approach. Extracts from Mentha aquatica showed strong antioxidant activity, but on the other hand, extracts from Mentha piperita showed no antioxidant activity.
Ključne besede: preservatives, Listeria monocytogenes, Staphylococcus aureus, antimicrobial activity, antioxidant activity, mint extracts
Objavljeno: 21.04.2011; Ogledov: 1900; Prenosov: 83
.pdf Celotno besedilo (1,10 MB)

3.
GRAPE ANTIOXIDANTS - INFLUENCE OF PROCESSING PARAMETERS ON THEIR CONTENT AND ACTIVITY
Iva Ružić, 2012, doktorska disertacija

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.
Ključne besede: white grapes, white wine, maceration, antioxidant activity, polyphenols, extraction, PLE, SFE.
Objavljeno: 05.04.2012; Ogledov: 1870; Prenosov: 95
.pdf Celotno besedilo (5,65 MB)

4.
Particle formation using supercritical fluids
Željko Knez, 2006, pregledni znanstveni članek

Opis: Particle formation and the design of solid particles and powdery composites with unique properties is at the moment one of major the developments of supercritical fluid (synonyms: dense gases, dense fluids, high pressure) applications. Conventional well-known processes for the particle-size redistribution of solid materials are crushing and grinding (which for some compounds are carried out at cryogenic temperatures), air micronization, sublimation, and recrystallization from solution. There are several problems associated with the above-mentioned processes. Some substances are unstable under conventional milling conditions, in recrysfallization processes the product is contaminated with solvent and waste solvent streams are produced. The application of supercritical fluids may overcome the drawbacks of conventional processes, and powders and composites with special characteristics can be produced. Several processes for the formation and design of solid particles using dense gases have been studied intensively. The unique thermodynamic and fluid-dynamic properties of supercritical fluids can also be used for the impregnation of solid particles, for the formation of solid powderous emulsions, particle coatings, e.g. for the formation of solids with unique properties for use in different applications. This review will focus on the fundamentals and on recent advances of particle formation and design processes using supercritical fluids on their applications and the technological advantages and disadvantages of various processes.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Objavljeno: 31.05.2012; Ogledov: 1268; Prenosov: 30
.pdf Celotno besedilo (514,21 KB)
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5.
The peculiarities of cross-correlation between two secondary precursors - radon and magnetic field variations, induced by tectonic activity
Vitalii Danilovich Rusov, V. Yu. Maksymchuk, Radomir Ilić, V.M. Pavlovych, V. G. Bakhmutov, D. N. Saranuk, V.M. Vaschenko, Jure Skvarč, Lucija Hanžič, S. I. Kosenko, 2006, drugi članki ali sestavki

Opis: A model of precursor manifestation mechanisms, stimulated by tectonic activityand some peculiarities of observer strategy, whose main task is the effective measurement of precursors in the spatial area of their occurrence on the Earth's daylight, are considered. In particular, the applicability of Dobrovolsky's approximation is analyzed, when an unperturbed medium (characterized by the simple shear state) and the area of tectonic activity (local inhomogeneity caused by the change only of shear modulus) are linearly elastic, and perturbation, in particular, surface displacement is calculated as a difference of the solutions of two independent static problems of the theory of elasticity with the same boundary condition on the surface. Within the framework of this approximation a formula for the spatial distribution (offirst component) of magnetic field variations caused by piezomagnetic effect in the case of perturbed regular medium, which is in simple shear state is derived. Cogent arguments in favor of linear dependence between the radon spatial distribution and conditional deformation are obtained. Changes in magnetic field strength and radon concentrations were measured along a tectonomagnetic profile of the total length of 11 km in the surroundings of the "Academician Vernadsky" Station on the Antarctic Peninsula (W 64 16', S 6515'). Results showed a positive correlation between the annual surface radonconcentration and annual changes of magnetic field relative to a base point, and also the good coincidence with theoretical calculation.
Ključne besede: geophysics, tectonic activity, radon, precursors
Objavljeno: 31.05.2012; Ogledov: 1043; Prenosov: 20
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6.
Enzymatic synthesis of sugar fatty acid esters in organic solvent and in supercritical carbon dioxide and their antimicrobial activity
Maja Leitgeb, Saša Šabeder, Željko Knez, 2008, izvirni znanstveni članek

Opis: Lipase-catalyzed synthesis of different sugar fatty acid esters was performed in high yields in 2-methyl-2-butanol at atmospheric pressure and in supercritical carbon dioxide (SC CO2) at 10 MPa. Influence of molecular sievesconcentration on conversion in SC CO2 was studied. Growth inhibitory effect of commercial sucrose fatty acid esters and enzymatically synthesized sucrose and fructose fatty acid esters on Gram-positive and Gram-negative micro-organisms, as well as on yeast was tested. Sucrose laurate inhibited the growth of Bacillus cereus food poisoning bacteria at a concentration of 9.375 mg/ml.
Ključne besede: biocatalysis, lipase, sugar fatty acid ester, organic solvent, cupercritical CO2, antimicrobial activity
Objavljeno: 31.05.2012; Ogledov: 1168; Prenosov: 38
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7.
8.
Comparison of the esterification of fructose and palmitic acid in organic solvent and supercritical carbon dioxide
Saša Šabeder, Maja Leitgeb, Željko Knez, 2005, izvirni znanstveni članek

Opis: Sugar fatty acid esters are nonionic surfactants, which are used for personal care products, cosmetic applications, and as emulsifiers for food. In recent years, enzymatic synthesis of sugar fatty acid esters is attracting keen attention as a new manufacturing method for future application. Reaction parameters of lipase-catalyzed synthesis of fructose fatty acid esters in organic solvent were optimized in a batch reactor at atmospheric pressure. Optimum conditions for reaction performed in organic solvent at atmospheric pressure were 10% (wžw of substrates) of lipase from Candida antarctica B, 12.14% (wžw of reaction mixture) of molecular sieves at 60 C, and stirring rate of 600 rpm. Esterification of fructose and palmitic acid was performed insupercritical carbon dioxide with and without addition of cosolvent (organicsolvent) at 60 C. Effect of pressure on enzyme activity was studied.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, esterification, organic solvent, lipase catalysed synthesis, fructose fatty esters, Candida antarctica B, enzyme activity
Objavljeno: 01.06.2012; Ogledov: 1132; Prenosov: 28
URL Povezava na celotno besedilo

9.
Stability of proteinase from Carica papaya latex in dense gases
Maja Leitgeb, Mateja Primožič, Željko Knez, 2005, izvirni znanstveni članek

Opis: Proteinase from Carica papaya latex was tested on its thermal stability at atmospheric pressure and in supercritical carbon dioxide, near-critical propane and dimethyl-ether. In supercritical carbon dioxide at 300 bar thermalactivation of the examined proteinase was improved in the comparison toatmospheric pressure. In propane and dimethyl-ether (300 bar) activity of the examined proteinase decreased. Influence of compressionžexpansion cycles on residual activity of the same proteinase in supercritical carbon dioxide (300 bar and 50 °C) was studied, as well. Different ways of transition from supercritical to low-pressure-state were used which affected residual activityof the proteinase.Addition of water in the system increased activity of proteinase from C. papaya, which was incubated in supercritical carbon dioxide for 24 h. Optimum amount of water was found to be between 0.5 and 0.7 g/L.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Objavljeno: 01.06.2012; Ogledov: 921; Prenosov: 13
URL Povezava na celotno besedilo

10.
Adsorption and antibacterial activity of soluble and precipitated chitosan on cellulose viscose fibers
Lidija Fras Zemljič, Tijana Ristić, Tina Tkavc, 2012, izvirni znanstveni članek

Opis: The aim and novelty of this work was to compare the adsorption of totally-soluble chitosan (acidic solution) against the adsorption of precipitated chitosan, onto cellulose fibers. The influences of both these chitosan-adsorption procedures on a final amino groupćs content in functionalized cellulose fibers were studied, using potentiometric titration and the conventional spectrophotometric C.I. Acid Orange 7 method. Surface modification and adsorption of chitosan were, in addition, monitored by determining XPS spectra. The antimicrobial activities of both chitosan- functionalised cellulose fibers were examined, in regard to pathogen bacteria and fungus.
Ključne besede: functionalized viscose, chitosan solution, precipitates, potentiometric titration, spectrophotometry, antimicrobial activity
Objavljeno: 01.06.2012; Ogledov: 1278; Prenosov: 133
.pdf Celotno besedilo (372,02 KB)
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