1. Specific fertilization practices reveal important insights into the complex interaction between microbes and enzymes in soils of different farming systemsMaša Kozmos, Ana Štuhec, Eva Tratnik, Tomaž Langerholc, 2024, original scientific article Abstract: The interaction of microorganisms and their enzyme activity is one of the key indicators for a comprehensive measurement of soil health. The aim of this study was to determine significant correlations between different soil microorganisms and enzyme activities of β-glucosidase, N-acetyl-glucosaminidase, urease, arylamidase, phosphatase, acid phosphatase, alkaline phosphatase, and arylsulfatase after supplementation with standard fertilizer, spent mushroom substrate and composed fertilizer in soils from conventional–integrated, organic and biodynamic farming. Samples were grouped according to the farming system and fertilization for all seasons. The biodynamic farm was the least affected by the different fertilizations, except for standard fertilization. Standard fertilizer caused negative correlations between the actinomycetes and the arylsulfatase in organic and biodynamic farms. The same fertilization affected the actinomycetes/phosphatase relationship differently, regardless of the basic soil structure. Actinomycetes correlated positively with acid phosphatase and urease in conventional–integrated and biodynamic farms after spent mushroom substrate, respectively. Arylamidase activity in relation to total microorganisms responded to fertilization with standard fertilizer and spent mushroom substrate independently of the basic soil structure. Fertilization can influence the soil microbe/enzyme relationships in different soils. Regardless of the basic soil structure, some of these relationships could be important indicators for further studies.
Keywords: agriculture, conventional-integrated, organic, biodynamic, fertilization, soil microorganisms, soil enzyme activity
Published in DKUM: 17.04.2025; Views: 0; Downloads: 3
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2. Enzyme activity and physiochemical properties of flour after supercritical carbon dioxide processingMaja Leitgeb, Željko Knez, Gordana Hojnik Podrepšek, 2022, original scientific article Abstract: The objectives of this study were to inactivate the enzymes α-amylase, lipase, protease,
and peroxidase in flour with supercritical carbon dioxide (scCO2), and to optimize the enzymatic
treatment conditions. Enzyme inactivation is important, due to the undesirability of certain flour
enzymes that cause adverse reactions during storage as unpleasant rancidity of flour, and, at the
same time, reduce the shelf life of flour. Therefore, crude enzymes and flour were initially exposed
to scCO2 to determine the effect on specific enzyme activity under appropriate conditions. The
activity of the unwanted enzymes lipase and peroxidase decreased under optimal process conditions
of scCO2 exposure, lipase by 30%, and peroxidase by 12%, respectively. It was discovered that the
inactivation of enzymes in wheat flour occurred, where, at the same time, this sustainable method
allows the regulation of enzyme activity in the baking process. Afterwards, the effect of scCO2 on the
physicochemical properties of flour, morphological changes on starch granules, and content of total
lipids was studied. In scCO2-treated white wheat flour, the fat content decreased by 46.15 ± 0.5%,
the grain structure was not damaged, and the bread as the final product had a lower specific surface
volume. Therefore, this could be a promising technology for flour pretreatment, potentially impacting
the prolonging of its shelf-life.
Keywords: enzymes, enzyme activity, proteins, supercritical fluids, wheat flour
Published in DKUM: 10.04.2025; Views: 0; Downloads: 1
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3. Use of non-conventional cell disruption method for extraction of proteins from black yeastsMaja Čolnik, Mateja Primožič, Željko Knez, Maja Leitgeb, 2016, original scientific article Abstract: The influence of pressure and treatment time on cells disruption of different black yeasts and on activities of extracted proteins using supercritical carbon dioxide process was studied. The cells of three different black yeasts Phaeotheca triangularis, Trimatostroma salinum, and Wallemia ichthyophaga were exposed to supercritical carbon dioxide (SC $CO_2$) by varying pressure at fixed temperature (35°C). The black yeasts cell walls were disrupted, and the content of the cells was spilled into the liquid medium. The impact of SC $CO_2$ conditions on secretion of enzymes and proteins from black yeast cells suspension was studied. The residual activity of the enzymes cellulase, $beta$-glucosidase, $alpha$-amylase, and protease was studied by enzymatic assay. The viability of black yeast cells was determined by measuring the optical density of the cell suspension at 600 nm. The total protein concentration in the suspension was determined on UV–Vis spectrophotometer at 595 nm. The release of intracellular and extracellular products from black yeast cells was achieved. Also, the observation by an environmental scanning electron microscopy shows major morphological changes with SC $CO_2$-treated cells. The advantages of the proposed method are in a simple use, which is also possible for heat-sensitive materials on one hand and on the other hand integration of the extraction of enzymes and their use in biocatalytical reactions.
Keywords: P. triangularis, W. ichtyophaga, T. salinum, supercritical carbon dioxide, enzyme activity, cells
Published in DKUM: 10.07.2017; Views: 1546; Downloads: 407
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4. Stability of proteinase from Carica papaya latex in dense gasesMaja Leitgeb, Mateja Primožič, Željko Knez, 2005, original scientific article Abstract: 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.
Keywords: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Published in DKUM: 01.06.2012; Views: 2015; Downloads: 28
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5. Comparison of the esterification of fructose and palmitic acid in organic solvent and supercritical carbon dioxideSaša Šabeder, Maja Leitgeb, Željko Knez, 2005, original scientific article Abstract: 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.
Keywords: chemical processing, high pressure technology, supercritical CO2, esterification, organic solvent, lipase catalysed synthesis, fructose fatty esters, Candida antarctica B, enzyme activity
Published in DKUM: 01.06.2012; Views: 2400; Downloads: 211
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6. Particle formation using supercritical fluids : a short reviewŽeljko Knez, 2006, review article Abstract: 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.
Keywords: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Published in DKUM: 31.05.2012; Views: 2888; Downloads: 195
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