Željko Knez

Comparison of antioxidative and synergistic effects of rosemary extract with α-tocopherol, ascorbyl palmitate and citric acid in sunflower oil

The antioxidative activities of four natural antioxidants: rosemary extract (ROS.CON), α-tocopherol (TOC), ascorbyl palmitate (AP) and citric acid (CA) were studied in sunflower oil stored at 60° C. Among them, rosemary extract (ROS.CON) exhibited the best antioxidative activity, as determined by peroxide and anisidine value measurements. α-Tocopherol showed a prooxidative effect on stability of sunflower oil at tested conditions. The synergistic effects of α-tocopherol (TOC), ascorbyl palmitate (AP) and citric acid (CA) on rosemary extract (ROS.CON) were investigated. When combined with citric acid and especially ascorbyl palmitate, the rosemary extract showed an additive antioxidative effect, while by mixture with α-tocopherol a negative synergism was observed.

Phase equilibrium (solid-liquid-gas) in polyethyleneglycol-carbon dioxide systems

Phase equilibria (solid-liquid-gas) for polyethyleneglycol (with molar masses 1500, 4000, 8000 and 35 000 g mol−1) and carbon dioxide mixtures were determined. It was found that the S-L-V lines in P-T projection for all polyethyleneglycols studied show a temperature minimum and a temperature maximum. These phenomena have not been reported previously in the literature. If a reduced temperature (obtained by dividing the temperature of the solid-liquid transition under pressure by the melting point of PEG at 1 bar) is introduced, the S-L transition of all binary systems are represented by one line. The solubility of CO2 in liquid polyethyleneglycols is influenced by pressure and temperature, and is almost independent of the molecular mass of polyethyleneglycol. In a P-T projection, the vapour-liquid equilibrium is represented by a straight line if isopleths are plotted as a function of the reduced temperature. By combining the P-Tred projections of the S-L and L-V transitions, one master diagram can obtained which is valid for all binary mixtures of polyethyleneglycol and CO2 in the pressure and temperature range investigated.

Solvent extraction study of antioxidants from Balm (Melissa officinalis L.) leaves

In the paper, the extraction of antioxidants from Balm (Melissa officinalis L.) leaves with ethanol is presented. Effects of particle size, amount of solvent and temperature on the extraction rates and concentrations of antioxidants in the extracts were studied and kinetics was determined. Individual antioxidants (carnosic, ursolic and oleanolic acids) were identified by high performance liquid chromatography. Results showed that the intraparticle diffusion was the rate-governing step of the extraction process. The extractions all proceeded in three stages: an initial washing stage, a fast stage and a slower stage. Experimental extraction curves were analysed with a mathematical model derived from Ficks second law, and diffusion coefficients of the antioxidants within the particles under different operating conditions in ethanol were determined.

Compressed gases as alternative enzymatic-reaction solvents: a short review

Abstract Application of supercritical fluids and liquid gases as an alternative reaction medium for enzyme-catalysed reactions is presented. The factors affecting the enzyme stability in supercritical fluids (effect of water activity, effect of pressure and temperature, number of pressurisation–depressurisation steps) and inhibition of enzymes are well documented with experimental results on hydrolases. An overview of our research on various types of HP enzymatic batch-stirred-tank-, continuous-packed-bed- and continuous-membrane reactors to obtain data on productivity and to evaluate the economy of the process is given.

Hydrothermal reactions of agricultural and food processing wastes in sub- and supercritical water: a review of fundamentals, mechanisms, and state of research.

Hydrothermal (HT) reactions of agricultural and food-processing waste have been proposed as an alternative to conventional waste treatment technologies due to allowing several improvements in terms of process performance and energy and economical advantages, especially due to their great ability to process high moisture content biomass waste without prior dewatering. Complex structures of wastes and unique properties of water at higher temperatures and pressures enable a variety of physical-chemical reactions and a wide spectra of products. This papers aim is to give extensive information about the fundamentals and mechanisms of HT reactions and provide state of the research of agri-food waste HT conversion.

Solubility of β-carotene and oleic acid in dense CO2 and data correlation by a density based model

Abstract The equilibrium solubilities of β-carotene and oleic acid have been measured in liquid and supercritical CO2 using a static method. The measurements were performed in the pressure range from 100 to 300 bar at temperatures 25 °C and 40 °C for β-carotene and at temperatures 30 °C, 40 °C and 50 °C for oleic acid. The experimental data were correlated by use of the density based model proposed by Chrastil. The same model was used for correlation of the literature solubility data of capsaicin in CO2.

Polyphenols: Extraction Methods, Antioxidative Action, Bioavailability and Anticarcinogenic Effects

Being secondary plant metabolites, polyphenols represent a large and diverse group of substances abundantly present in a majority of fruits, herbs and vegetables. The current contribution is focused on their bioavailability, antioxidative and anticarcinogenic properties. An overview of extraction methods is also given, with supercritical fluid extraction highlighted as a promising eco-friendly alternative providing exceptional separation and protection from degradation of unstable polyphenols. The protective role of polyphenols against reactive oxygen and nitrogen species, UV light, plant pathogens, parasites and predators results in several beneficial biological activities giving rise to prophylaxis or possibly even to a cure for several prevailing human diseases, especially various cancer types. Omnipresence, specificity of the response and the absence of or low toxicity are crucial advantages of polyphenols as anticancer agents. The main problem represents their low bioavailability and rapid metabolism. One of the promising solutions lies in nanoformulation of polyphenols that prevents their degradation and thus enables significantly higher concentrations to reach the target cells. Another, more practiced, solution is the use of mixtures of various polyphenols that bring synergistic effects, resulting in lowering of the required therapeutic dose and in multitargeted action. The combination of polyphenols with existing drugs and therapies also shows promising results and significantly reduces their toxicity.

Diffusion of methanol–liquid CO2 and methanol–supercritical CO2 in silica aerogels

Drying of alcogel is the most critical step in production of transparent and monolithic silica aerogel. If alcohol extraction with liquid or supercritical carbon dioxide is used, diffusion of alcohol through the alcogel to the CO2 plays an important role. Dependent on the diffusion times, the quality and shape of aerogel samples vary from cracked (short diffusion times) to transparent crack-free aerogels (long diffusion times). At medium diffusion times, the non-transparent area was observed inside the aerogel samples. Diffusion coefficients of methanol in the liquid CO2 at two different temperatures and the diffusion coefficient of methanol in supercritical CO2 inside the silica aerogel were determined from the dependence of the width of the non-transparent damage area on diffusion times.

Supercritical impregnation of drugs and supercritical fluid deposition of metals into aerogels

The presented review covers the latest research on supercritical impregnation into organic and inorganic aerogels by investigating those factors that influence the impregnation. Supercritical impregnation is a promising method for incorporating drugs within porous carriers including for water insoluble drugs. An additional step (reduction from metallic precursor to metal) is required for the supercritical impregnation of metallic precursors. Hence, this expanded method is preferably termed as supercritical fluid deposition or adsorption. Supercritical impregnation of drugs, as well as metals, are mostly influenced by interactions between the compound and aerogel matrix, supercritical impregnation conditions, and the characteristics of a compound within a supercritical fluid.

Solubility of capsaicin in dense CO2

The equilibrium solubilities of capsaicin in liquid and supercritical CO2 were measured by a staticanalytical method in the pressure range from 70 to 400 bar at temperatures of 25, 40, and 60°C. The data were correlated by use of the thermodynamic model relating the solubility to the solvent density and a model for the dependence of the enhancement factor on the density of the solvent.