Effect of Filtrated Osmotic Solution Based on Concentrated Chokeberry Juice and Mint Extract on the Drying Kinetics,Energy Consumption and Physicochemical Properties of Dried Apples

Background: Filtration of osmotic solution affects selective penetration during osmotic dehydration (OD), and after drying is finished, this can influence the chemical composition of the material, which is also modified by OD. Methods: Osmotic dehydration was carried out in filtrated and non-filtrated concentrated chokeberry juice with the addition of mint infusion. Then, this underwent convective drying, vacuum-microwave drying and combined convective pre-drying, followed by vacuum-microwave finishing drying. Drying kinetics were presented and mathematical models were selected. The specific energy consumption for each drying method was calculated and the energy efficiency was determined. Results and Discussion: The study revealed that filtration of osmotic solution did not have significant effect on drying kinetics; however, it affected selective penetration during OD. The highest specific energy consumption was obtained for the samples treated by convective drying (CD) (around 170 kJ·g⁻¹ fresh weight (fw)) and the lowest for the samples treated by vacuum-microwave drying (VMD) (around 30 kJ·g⁻¹ fw), which is due to the differences in the time of drying and when these methods are applied. Conclusions: Filtration of the osmotic solution can be used to obtain the desired material after drying and the VMD method is the most appropriate considering both phenolic acid content and the energy aspect of drying.     

Concentration of noni juice by means of osmotic distillation

Osmotic distillation (OD) or osmotic evaporation (OE) is a promising membrane process generally applied to concentrate solutions under isothermal conditions. In this work, this process was applied to concentrate commercial noni juice (Morinda citrifolia). Several nutraceutical properties have been reported for noni-derived products, mainly associated to the phenolic content of the fruit.The analyzed system is an osmotic distillation system where the solutions are circulated through a hollow fiber membrane contactor operating in transient configuration with circulation rates between 0.1 and 1.0 L min⁻¹ and concentrated solutions of CaCl₂ were used as extraction brine. At isothermal conditions (30 °C), transmembrane vapor water flux was experimentally determined from 0.090 up to 0.413 kg h⁻¹ m⁻². Noni juice was concentrated from 8 to 32 °Brix after 60 min of treatment. The content of phenolic compounds was preserved after this processing.Simulation algorithms based on phenomenological equations of heat and mass transfer were developed considering a resistances-in-series model to predict the performance of the process from theoretical information. The values of transmembrane water flux obtained by simulations showed deviations between 2.35 and 16.19% with the experimental ones for the operating conditions applied in this work.     

Effect of process parameters on transmembrane flux during direct osmosis

Direct osmosis is a non-thermal membrane process employed for the concentration of fruit juices at ambient temperature and atmospheric pressure, thereby maintaining the organoleptic and nutritional properties of fruit juices. In the present study, concentration of pineapple juice by direct osmosis was explored. Aqueous solution of sucrose (0–40%, w/w)–sodium chloride (0–26%, w/w) combination was investigated as an alternative osmotic agent. The sucrose–sodium chloride combination can overcome the drawback of sucrose (low flux) and sodium chloride (salt migration) as osmotic agents during direct osmosis process. The effect of the hydrodynamic conditions in the module and feed temperature (25–45 °C) on transmembrane flux was evaluated. For a range of hydrodynamic conditions studied, it was observed that transmembrane flux increases with Reynolds number. The increase in feed temperature resulted in an increase in transmembrane flux. The pineapple juice was concentrated upto a total soluble solids content of 60 °Brix at ambient temperature. The effect of direct osmosis process on physico-chemical characteristics of pineapple juice was also studied. The ascorbic acid content was well preserved in the pineapple juice concentrate by direct osmosis process.     

Combined Effect of Impregnation with an Origanum vulgare Infusion and Osmotic Treatment on the Shelf Life and Quality of Chilled Chicken Fillets

The scope of this work is the study of a combined process including a dipping step into an oregano (Origanum vulgare ssp. hirtum) infusion (OV) followed by osmotic treatment of chicken fillets at 15 °C. Chicken fillets were immersed in an osmotic solution consisting of 40% glycerol and 5% NaCl with (OV/OD) and without (OD) prior antioxidant enrichment in a hypotonic oregano solution. A comparative shelf life study of all the samples (untreated, OD and OV/OD treated) was then conducted at 4 °C in order to assess the impact of this process on the quality and shelf life of chilled chicken fillets. Microbial growth, lipid oxidation and color/texture changes were measured throughout the chilled storage period. Rates of microbial growth of pretreated fillets were significantly reduced, mainly as a result of water activity decrease (OD step). Rancidity development closely related to off odors and sensory rejection was greatly inhibited in treated fillets owing to both inhibitory factors (OD and OV), with water-soluble phenols (OV step) exhibiting the main antioxidant effect. Shelf life of treated chicken fillets exhibited a more than three-fold increase as compared to the untreated samples based on both chemical and microbial spoilage indices, maintaining a positive and pleasant sensory profile throughout the storage period examined.     

The Use of Antioxidant Potential of Chokeberry Juice in Creating Pro-Healthy Dried Apples by Hybrid (Convection-Microwave-Vacuum) Method

The visible trend in the development of the snack market focuses on the use of innovative technologies such as low-temperature or hybrid processes that allow the preservation of native ingredients of raw plant materials. In addition, the high antioxidant potential of, for example, chokeberry fruit can be used to support technological processes and create new products. The aim of the study was to evaluate the possibility of using chokeberry juice concentrate as a component of an osmotic solution to enrich apple samples with natural bio-ingredients and obtain dried apples with increased content of ingredients with antioxidant properties; pro-healthy apple chips. The research material consisted of apples that underwent osmotic dehydration in solutions of sucrose or sucrose and chokeberry juice concentrate and then were dried by the freeze-drying or the hybrid method. The freeze-drying was more beneficial for maintaining the vitamin C content, while the use of the hybrid method resulted in the preservation of more polyphenolic compounds. The sensory evaluation indicated the need to modify the composition of the osmoactive solution. Due to the use of chokeberry juice concentrate, the content of vitamin C, polyphenols, and the antioxidant activity of dried apples was increased.     

稀溶液中化学势的计算以及渗透压公式的推导

将溶液中某组分化学势的计算方式归纳为两种:(1)利用气液平衡时,溶液中某组分的化学势和气相中该组分的化学势相等这一关系来计算;(2)利用溶液中某组分化学势的全微分表达式直接积分来计算。在此基础上,给出了渗透压公式的一种新推导方式,并指出部分物理化学教材关于渗透压定义(Π=p2-p1)的不合理性以及推导渗透压时存在的不妥之处。     

Concentration Polarization of Interacting Solute Particles in Cross-Flow Membrane Filtration

A theoretical approach for predicting the influence of interparticle interactions on concentration polarization and the ensuing permeate flux decline during cross-flow membrane filtration of charged solute particles is presented. The Ornstein-Zernike integral equation is solved using appropriate closures corresponding to hard-spherical and long-range solute-solute interactions to predict the radial distribution function of the solute particles in a concentrated solution (dispersion). Two properties of the solution, namely the osmotic pressure and the diffusion coefficient, are determined on the basis of the radial distribution function at different solute concentrations. Incorporation of the concentration dependence of these two properties in the concentration polarization model comprising the convective-diffusion equation and the osmotic-pressure governed permeate flux equation leads to the coupled prediction of the solute concentration profile and the local permeate flux. The approach leads to a direct quantitative incorporation of solute-solute interactions in the framework of a standard theory of concentration polarization. The developed model is used to study the effects of ionic strength and electrostatic potential on the variations of solute diffusivity and osmotic pressure. Finally, the combined influence of these two properties on the permeate flux decline behavior during cross-flow membrane filtration of charged solute particles is predicted. Copyright 1999 Academic Press.     

Glucose and fructose levels on grape skin: interference in Lobesia botrana behaviour

The vineyard produces one of the most important crops in Portugal and is affected by various pests, such as the Lobesia botrana moth, which can be attracted chemically by compounds on the grape skin.In this study, the sugar contents (glucose and fructose) on grape skin were analysed for five Portuguese Vitis vinifera grape varieties and compared in grape juice and whole grapes. Samples were harvested in July, August and September of 2001 and 2002.The quantification was attained employing a new methodology, which comprised the preparation of a methanol solution to extract the compounds from the grape skin and further chromatographic analyses by liquid chromatography (LC) with refractive index (RI) detection. The samples designated by whole grapes were homogenised, centrifuged and filtrated, while the juice was obtained by crushing and filtration.Grape skin has shown higher levels of glucose than fructose, but both compounds increased from green berry (July) to veraison (August) and had a slight decrease from veraison to harvest (September).As expected, the glucose and fructose contents (total sugar) were higher in the whole grape than in the juice and much higher than in the grape skin itself. For Loureiro and Trajadura varieties, the levels of both sugars on grape skin were very similar. This resemblance strengthened the statement of the decisive role of this parameter in female L. botrana oviposition behaviour.     

Membrane equilibria in concentrated polymer solutions

Membrane equilibria in concentrated polymer solutions are investigated. A three-component system (solvent, a polymer and an arbitrary solute) is considered. Starting with the virial expansion of the osmotic pressure, the Gibbs-Duhem equation for the system is integrated and the chemical potentials of the different components are evaluated. From the latter the equilibrium conditions are derived for a variety of experimental situations. The treatment is extended to the study of partition equilibria in gels, using a concentrated polymer solution as a model for the gel.     

Cu(Ⅱ)印迹壳聚糖交联多孔微球去除水溶液中金属离子

研究了以Cu2+为模板的壳聚糖交联多孔微球(Cu-CSCPM)对溶液中Cu2+的吸附性能,为该材料应用于去除废水、果蔬汁等有毒重金属铜离子提供理论基础。首先制备了Cu2+印迹壳聚糖交联多孔微球,并表征了微球的一些物理化学性质;其次采用静态吸附法研究了该微球对Cu2+的吸附行为。结果发现,制得的微球表面多孔,含有活性-NH2,其含水量为69.59%,树脂骨架密度为1.22g/cm3,孔度值为73.68%,交联度为82.42%。初始浓度为60mmol/L、吸附温度40℃、pH=4.0时,Cu-CSCPM对Cu2+的饱和吸附容量为1.89mmol/g。Cu-CSCPM再生5次对Cu2+仍然具有较高吸附容量。     

聚丙烯腈溶液的凝胶化研究

聚丙烯腈是用途最广泛的聚合物之一,其溶于适当溶剂中形成的聚丙烯腈溶液是制备聚丙烯腈纤维、渗透膜等高分子材料的原料。聚丙烯腈溶液的物理化学性质对所制备材料的性能有很大的影响。本文对高分子溶液的凝胶化和高分子凝胶的特点做了简要介绍,并介绍了聚丙烯腈及其凝胶的特点。根据高分子浓溶液体系的特点提出用于表征聚丙烯腈溶液凝胶化的主要方法。从浓度和温度对聚丙烯腈溶液凝胶化行为的影响、熟化和非溶剂对聚丙烯腈溶液凝胶化行为的影响、聚丙烯腈溶液凝胶化的热可逆性、聚丙烯腈溶液凝胶化的分形特征以及聚丙烯腈凝胶的交联机理这几个方面对已有聚丙烯腈溶液的凝胶化研究成果和最新进展进行了综述。最后对聚丙烯腈溶液凝胶化和聚丙烯腈凝胶的研究前景做了展望。     

Concentration and temperature polarization effects during osmotic membrane distillation

Pineapple juice is one of the popular fruit juice due to its pleasant aroma and flavor. Concentration of clarified pineapple juice was carried out by osmotic membrane distillation in a plate and frame membrane module. Concentration and temperature polarization effects are found to have significant role on flux reduction during osmotic membrane distillation process. The contribution of these polarization effects on reduction of the driving force (in turn the flux) at various process conditions such as osmotic agent concentration (2–10 mol/kg (1 molality = 1 mol/kg)), flow rate (25–100 ml/min) of feed and osmotic agent are studied. Concentration polarization has more significant effect on flux reduction when compared to temperature polarization. The experimental fluxes were in good agreement with theoretical fluxes when calculated by considering both concentration and temperature polarization effects. The pineapple juice was concentrated up to a total soluble solids content of 62°Brix at ambient temperature.     

Antioxidant potential and authenticity of some commercial fruit juices studied by EPR and IRMS

Antioxidant status of foods, plant, or fruit products is generally characterized by means of spectroscopic methods. Methods like HPLC, UV-VIS, or MS spectroscopy are used to understand the chemical and physical properties of different samples, and also EPR spectroscopy seems to be a valuable tool to characterize antioxidant activity of juice beverages. In this technique, certain antioxidants present in fruit juices interact with free radicals interrupting the chain reaction that can possibly damage essential molecules. Recording the EPR signal decay caused by the reaction with a natural or artificial reducing agent, it is possible to draw conclusions about the antioxidant capability of materials. IRMS is a powerful tool to distinguish between an authentic fruit juice and a juice obtained by concentrate dilution. This technique allows also the detection of commercial C₄ cane or corn derived sugar syrups in C₃ fruit juices. In the present study, four commercial fruit juices were investigated using stable isotope measurements (oxygen, hydrogen, and carbon) and EPR measurements in order to check the correct labeling in the Romanian markets and to compare antioxidant activity of the studied juices and the reference. It was proven that the number of paramagnetic species decreases in time with different reaction rates and this was correlated with the antioxidant activity of the studied juices. Stable isotope ratio measurements have demonstrated that the fruit juices studied were reconstructed from concentrates with tap water, according to their label.     

Stripping Voltammetric Analysis of Mercury at Base-treated Graphene Oxide Electrodes

According to the Rourke's model, graphene oxide(GO) synthesized from the oxidation of graphite actually consisted of partly oxidized graphene sheets and highly oxidized debris(OD). The OD was strongly adhered to the surface of graphene sheets, while they could be facilely removed by a base-washing procedure. The existence and removal by base-washing of OD were characterized by means of thermogravimetric analysis(TGA), FTIR spectroscopy, X-ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM) and Raman spectroscopy. The adsorption of OD not only made a great difference to the physical and chemical properties of GO, but also affected its electrochemical behavior when it was employed as an electrode material. In this article, we demonstrated that the electrochemical deposition and the subsequent voltammetric stripping analysis of mercury were significantly influenced by the presence of OD. The consequence suggests that the presence of OD on the sheets of GO restricts the electrochemical deposition behavior of mercury and further lowers the sensitivity of the voltammetric stripping responses. The sensitivity was observed as 0.78 A·L·mol^-1 at base-washed(bw)-GO/GC(glassy carbon) better than that at as-prepared GO(a-GO)/GC for 0.28 A·L·mol^-1. The limit of detection was calculated as 2.95 and 0.83 μmol/L before and after removing the OD, respectively. The availability of both electrodes was evaluated by detecting Hg²⁺ in lake water specimens using standard samples recovery.     

Unsteady state flux response: a method to determine the nature of the solute and gel layer in membrane filtration

The unsteady-state permeate flux response to a step change in transmembrane pressure is shown to result in unique flux–pressure profiles for the three types of solutes common in membrane ultrafiltration (UF): (a) solutes which exert an osmotic pressure but do not form a ‘gel’; (b) solutes which do not exert an osmotic pressure but form a ‘gel’ and (c) solutes which exert an osmotic pressure and also form a ‘gel’. It is also shown that for stirred cell UF, changes in the bulk feed solution properties (concentration, volume) are negligible on the time scale needed to attain a stable permeate flux. Unsteady-state permeate flux measurements could therefore be made at short filtration times so that the results would not be masked by changes in bulk properties.     

Differential sorption in viscoelastic fluids

The diffusion of organic solvents in concentrated polymer solutions often deviates from the predictions of Fick's second law, especially when the solution is in the glassy state; such behavior is called anomalous or non-Fickian. This paper analyzes the one-dimensional sorption of a solvent into a concentrated polymer solution under a small driving force. The treatment includes the effect of an entanglement network on the process as postulated by Thomas and Windle. The deformation of the entanglement network during sorption creates a normal stress on the solvent equivalent to an osmotic pressure. Including the osmotic pressure gradient in the driving force for solvent diffusion leads to a linear, third-order partial differential equation for solvent concentration distributions. By evaluating the physical constants in the theory for the system methyl acetate/poly(methyl methacrylate) at 30°C the treatment is shown to predict the anomalous characteristics found experimentally.     

The isolation of some polynuclear aromatic hydrocarbons from aqueous samples by means of reversed-phase concentrator columns

The results for some polynuclear aromatic hydrocarbons (PAH) in canal water and rain water differ depending on whether the PAH are concentrated directly on Sep- Pak C-18 cartridges or concentrated after filtration with further analysis of the particulate matter. For canal waters, higher total PAH concentrations are obtained when the suspended material is also analyzed.     

Experimental study of membrane distillation with brine circulated in the cold side

A membrane distillation (MD) process with brine circulated in the cold side was developed. This process combines the ordinary MD with the osmotic distillation (OD), and is therefore called membrane osmotic distillation (MOD). The effects of brine concentration, liquid temperature, temperature difference between the warm and cold sides and liquid flow rate on water flux and heat efficiency of the process were investigated. Comparisons of MOD with MD and OD were carried out. It was found that MOD has the advantage of achieving higher water flux and heat efficiency simultaneously. A relation of the MOD water flux to the MD and OD water fluxes was given.     

Principles of Osmotic Desalination

Salt solutions can be separated into pure water and concentrated salt solution by reverse osmosis using semipermeable membranes. The distinct features and limitations of osmotic separations are developed from a consideration of the pertinent solution properties and the conditions inherently to be met by the membranes, seen as interacting barrier phase in a process which substantially separates water from water.     

校准蒸发光散射检测器选用标准物质的比较与分析

通过对葡萄糖和三氯蔗糖的物理、化学性质的比较,采用高效液相色谱仪和蒸发光散射检测器进行标准溶液色谱峰面积的检测,并用G rubbs检验法对其数据进行异常值检验。结果表明,三氯蔗糖相对于葡萄糖较为稳定,选用三氯蔗糖作为蒸发光检测器校准用标准物质比较合适。