Pressurized Hot Water Extraction of anthocyanins from red onion: A study on extraction and degradation rates

Pressurized Hot Water Extraction (PHWE) is a quick, efficient and environmentally friendly technique for extractions. However, when using PHWE to extract thermally unstable analytes, extraction and degradation effects occur at the same time, and thereby compete. At first, the extraction effect dominates, but degradation effects soon take over. In this paper, extraction and degradation rates of anthocyanins from red onion were studied with experiments in a static batch reactor at 110 °C. A total extraction curve was calculated with data from the actual extraction and degradation curves, showing that more anthocyanins, 21-36% depending on the species, could be extracted if no degradation occurred, but then longer extraction times would be required than those needed to reach the peak level in the apparent extraction curves. The results give information about the different kinetic processes competing during an extraction procedure.     

亚临界水中超声激励空化泡动力学分析

考察亚临界水中压力和温度对超声空化泡动力学的影响。应用非线性Rayleigh-Plesset方程模拟空化泡运动过程,并利用Matlab软件编程求数值解,用碘量法测定超声在亚临界水中的声空化产额。结果表明:当亚临界水的压力相似文献   

Reversed-phase retention thermodynamics of pure-water mobile phases at ambient and elevated temperature

The use of pure water at superheated temperatures, between 100 and 200 degrees C, as a mobile phase for reversed-phase separations is explored. The thermodynamics of the retention process at low temperature (15-55 degrees C) are compared to the thermodynamics at elevated temperature (125-175 degrees C). Significant differences in the enthalpy of the retention process are observed between the two temperature ranges. This is possibly due to changes in the hydrogen-bond network of the pure-water mobile phase, which would change the solvation, and therefore retention, of non-polar solutes. The change in thermodynamic values between the two temperature regions invalidates extrapolation of retention as a function of temperature between the two temperature regions for the prediction of room-temperature pure-water retention factors. The thermodynamic changes observed as the temperature is increased are similar to those seen when mobile phase composition is changed (by adding organic modifier) at constant temperature.     

Effect of the carbon dioxide modifier on the lipid composition of wool wax extracted from raw wool

Wool wax or lanolin is a unique substance secreted by sheep and forms a natural protective coating on wool fibres. It is widely used in pharmaceutical and cosmetic formulations. However, different systems of wool wax recovery from scouring liquour provide a dark impurified greasy product. This product has a lipid composition that differs from the wool wax present on wool fibres. The wool wax extraction method from raw wool with pressurised CO₂ and different modifiers at constant pressure and temperature was studied. Thin-layer chromatography coupled to an automated flame ionisation detection system (TLC/FID) was used to analyse the different lipid classes present in the collected extracts. Moreover, a detailed structural comparison of the cholesteryl esters and hydroxycholesteryl esters was carried out by means of sub-ambient pressure chromatography mass spectrometry in the electron impact and in the ammonia positive chemical ionisation modes. For comparison, qualitative and quantitative analyses of the lanolin extracted in Soxhlet with dichloromethane and commercial cosmetic lanolin were carried out. Differences in the quantity of wool wax extraction and in the lipid composition of different wool wax extracts were detected by changing the modifier polarity.     

Phenanthrene degradation in subcritical water

Subcritical water (<374 °C and <221 bar) has unique characteristics such as dramatically decreased dielectric constant, surface tension, and viscosity with increasing temperature, allowing for dissolution and reaction of organics in high-temperature water to occur. Additionally, the dissociation constant of water at temperatures of 200-300 °C is three orders of magnitude greater than that of ambient water, which may also contribute to the reactivity of subcritical water with certain organic compounds. In this study, the degradation and oxidation of phenanthrene in subcritical water were investigated. Both deionized water and water with 3% hydrogen peroxide were used in the degradation and oxidation studies. The effect of temperature on degradation efficiency has been determined with a temperature range of 100-350 °C. When the temperature was increased from 150 to 350 °C, the amount of phenanthrene degraded varied from 6 to 243 μg in each milliliter of deionized water. However, these quantities were increased to 195 μg at 150 °C and 3680 μg at 350 °C in each milliliter of water with 3% hydrogen peroxide. Several degradation products including phenol, benzoic acid, and ketones were identified by using gas chromatography/mass spectrometry (GC/MS).     

Binary diffusion coefficients of phenolic compounds in subcritical water using a chromatographic peak broadening technique

Infinite dilution diffusion coefficients of certain phenolic compounds were measured as a function of temperature in water slightly acidified with formic acid using the Taylor dispersion method. The diffusion coefficients calculated using the chromatographic peak broadening technique were found to increase exponentially with an increase in the temperature. The diffusion coefficients of the selected phenolic compounds did not vary as a function of their molecular weights and the diffusion coefficients of the phenolic compounds increased as a function of temperature (from 2.16 × 10⁻¹⁰ m² s⁻¹ at 298 K to 5.79 × 10⁻¹⁰ m² s⁻¹ at 413 K for malvidin-3,5-diglucoside). However, for some phenolic compounds such as gallic acid monohydrate, quercetin-3-β-d-glucoside, protocatechuic acid and (−)-epicatechin, there were difficulties in making measurements above temperatures of 352 K, 372 K, 392 K and 413 K, respectively, due to thermal degradation of the phenolic compounds in water above these temperatures. The experimentally measured diffusion coefficients of the phenolic compounds were correlated as a function of temperature and solvent viscosity and were compared with those predicted using theoretical models. The validity of the Stokes-Einstein diffusion model in predicting the diffusion coefficients of the phenolic compounds in hot pressurized water was also evaluated.     

Retention mechanisms in subcritical water reversed-phase chromatography

Differences in the properties of subcritical water and conventional water/acetonitrile and water/methanol mobile phases for reversed phase separations are explored. Using van’t Hoff plots enthalpies and entropies of transfer are compared among the mobile phases while linear solvation energy relationships are used to quantify contributions to retention based on a solute's polarizability, dipolarity, hydrogen bond donating ability, hydrogen bond accepting ability, and molecular size. Results suggest the presence of acetonitrile or methanol in the mobile phase may decrease dispersive interactions of the solute with the stationary phase compared to subcritical water, thereby lowering enthalpic contributions to retention. Enthalpic contributions are found to drive the retention of a methylene group in all systems studied.     

亚临界水萃取-酶抑制法快速检测蔬菜中的灭多威农药

本文研究了蔬菜中灭多威农药的亚临界水萃取-酶抑制法快速检测技术.研究表明,在萃取温度70℃,萃取时间5 min,提取液的pH为8.0,提取液体积为5 mL的条件下,灭多威有最高萃取效率.将本法分别应用于测定模拟样品和实际样品,结果表明亚临界水萃取的萃取效率和精密度都要高于国家标准方法中的手摇振荡萃取.     

Towards more rational techniques for the isolation of valuable essential oils from plants

Attention is drawn to the use of new and clean alternative methods for the isolation of essential oils from plants. A critical overview is presented of conventional methods (based on either organic solvent extraction or distillation) and new alternatives (including microwave-assisted extraction (MAE) as well as supercritical CO₂ (SC-CO₂) extraction and subcritical water extraction). The advantages and disadvantages of each technique are reported and special emphasis is given to the use of continuous subcritical water extraction which emerges as clearly advantageous over conventional techniques (by avoiding the use of organic solvents and considerably shortening the extraction time, as well as increasing the efficiency) and recent techniques, such as MAE (by increasing the efficiency) and SC-CO₂ extraction (by avoiding the co-extraction of cuticular waxes and lipids and the need for a sample drying stage prior to extraction).     

Considerations for the design of swirl chambers for the cyclone cooling of turbine blades and for other applications with high swirl intensity

The focus of this study lies on turbulent incompressible swirling flows with high swirl intensity. A systematic parameter study is conducted to examine the sensitivity of the mean velocity field in a swirl chamber to changes in the Reynolds number, swirl intensity and channel outlet geometry. The investigated parameter range reflects the typical kinematic flow conditions found in heat transfer applications, such as the cooling of the turbine blade known as cyclone cooling. These applications require a swirl intensity, which is typically much higher than necessary for vortex breakdown. The resulting flows are known as flow regime II and III. In comparison to flow regime I, which denotes a swirling flow without vortex breakdown, these flow regimes are characterized by a subcritical behavior. In this context, subcritical means that the flow is affected by the downstream channel section. Based on mean velocity field measurements in various swirl chamber configurations, it is shown that flow regime III is particularly sensitive to these effects. The channel outlet geometry becomes a determining parameter and, therefore, small changes at the outlet can produce entirely different flow patterns in the swirl chamber. In contrast, flow regime II, as well as flow regime I and axial channel flows, are much less sensitive to changes at the channel outlet. The knowledge about the sensitivity of the flow in different flow regimes is highly relevant for the design of a cyclone cooling system. Cooling systems employing flow regime III can result in a weakly robust flow system that may change completely over the operating range. As a remedy, the swirl intensity needs to be decreased so that flow regime III cannot be reached, which, however, reduces the maximum achievable heat transfer in the cooling system. Alternatively, the flow has to transition back from flow regime III to flow regime II or I before the flow leaves the swirl chamber. Two practical methods are presented. These findings can be directly applied in the design processes of future cyclone cooling systems, and other applications of swirling flow.