Mechanisms of Extraction of Aroma Compounds from Foods, Using Adsorbents. Effect of Various Parameters

Due to their high adsorbing capacity, different solids (carbonaceous adsorbents, zeolites, and polymers) are used to extract and concentrate aroma compounds from foods. Adsorption mechanisms are described in two phases, a kinetic stage that involves the diffusion of the analytes within the adsorbent pores and a thermodynamic stage that can be described by adsorption isotherms. These two phases determine the extraction time and the capacity of the adsorbent for a given aroma compound. Several applications involving adsorbents or sorbents have been developed, including purge and trap, solid-phase microextraction (SPME), and stir bar sorptive extractions (SBSE), headspace sorptive extraction (HSSE), which now are widely used for aroma extractions. Different extraction modes (in the headspace or by immersion in the sample) can be used to recover aroma compounds in foods. The same adsorption mechanisms take place in both cases. Various parameters affecting the extraction kinetics and the capacity of the adsorbent have to be optimized when developing an extraction method. They can be divided into three groups: physicochemical characteristics of the adsorbent, including its porosity and hydrophobia; physicochemical characteristics of the aroma compounds (among them, two parameters play an important role, the sample/adsorbent partition coefficient, which determines the affinity for the adsorbent and the volumetric mass, which influences the diffusion in the adsorbent pores); and the extrinsic parameters that depend on the sampling conditions such as pH, temperature, gas or solvent flows, time, and composition of the sample. Several models used to determine the diffusivity and partition coefficient of aroma between the food sample and the adsorbents have been developed. They are useful to understand the behavior of aroma compounds in regards to various adsorbents and in selecting the adsorbent material with the greatest affinity for the target aroma compounds. Quantitative studies based on adsorbent extraction of volatiles have been carried out. Nevertheless, competition between analytes and the saturation of these materials are limiting parameters. Thus, new strategies (SBSE, HSSE) are being developed to avoid these limiting aspects of adsorbents in order to use them in a quantitative way.     

New approaches for studying the chemical diversity of natural resources and the bioactivity of their constituents

Natural products (NPs) have historically been an important source of lead molecules in drug discovery. However, the interest that the pharmaceutical industry has had in NPs has declined in part because of the lack of compatibility of traditional natural-product extract libraries with high-throughput screenings and the low hit rate. Furthermore, in contrast to the synthetic libraries, compounds from natural sources are likely to have complex structures which slow down the identification process and contribute to problems related to supply and manufacturing. In this paper, we summarise some of the strategies that are being developed in our research unit to address these issues. On one hand, differential screening strategies were established with the aim of identifying dynamically induced NPs from silent biosynthetic pathways in plants and fungi that had been exposed to different stress situations. On the other hand, high-resolution HPLC techniques were optimised for biological and chemical profiling of crude extracts. This led to an integrated platform for rapid and efficient identification of new drug-leads and biomarkers of interest that were based on miniaturised technological approaches and metabolomics.     

Photo- and thermal degradation of MDMO-PPV:PCBM blends

This paper is devoted to the study of the photo- and thermal-ageing of MDMO-poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene (PPV) blended with methano-fullerene[6,6]-phenyl C₆₁-butyric acid methyl ester ([60] PCBM), a commonly used active layer of organic solar cells. Thin films of MDMO-PPV, PCBM and MDMO-PPV:PCBM were submitted to photo- and thermal ageing in presence or in absence of oxygen. The modifications of the chemical structure of the materials were analysed by UV-visible and IR spectroscopies. Studying the degradation of pristine materials (MDMO-PPV and PCBM) permit the identification of the markers for characterizing the degradation of each component of the active layer. The degradation of MDMO-PPV was shown to involve a radicalar oxidation implying at first the ethers functions and secondly the double bonds; the photo-oxidation of PCBM was shown to involve the oxidation of its C₆₀ moiety. Photo-oxidation of MDMO-PPV:PCBM blends involved the degradation of both components and the presence of PCBM was observed to largely reduce the rate of degradation of MDMO-PPV in comparison with pristine MDMO-PPV. On a kinetic point of view, the same conclusion was obtained for thermo-oxidation and photolysis (irradiation in absence of oxygen). Our experimental results suggest that the decrease of the rate of degradation of MDMO-PPV in blended films during the three kind of ageing (hυ, T, O₂) is mainly related to the radical scavenging properties of the PCBM.     

Influence of various process steps on the reliability of PMOSFETs submitted to negative bias temperature instabilities

In this paper, we analyze the impact of various process steps on the reliability of PMOSFET’s submitted to Negative Bias Temperature Instabilities stress conditions. We give some evidence of the complete thermal anneal of interface states induced by NBTI and investigate the influence of the oxide thickness and of the final forming gas anneal. Then we show a NBTI lifetime improvement after a fluorine implant through the gate and an arsenic bulk doping value increase.     

Measurements of minimum ignition energy in premixed laminar methane/air flow by using laser induced spark

Reducing engine pollutant emissions and fuel consumption is an important challenge. Lean-burning engines are a promising development; however, such engines require high-energy ignition systems for typical working conditions (equivalence ratio, Φ < 0.7). Laser-induced ignition is envisaged as a way to obtain high-energy ignition as a result of progress that has been made in laser beam technology in terms of stability, size, and energy. This study investigated the minimum energy necessary to ignite a laminar premixed methane air mixture experimentally. A parametrical study was performed to characterize the effects of the flow velocity, equivalence ratio, and lens focal length on the minimum energy required for ignition. Experiments were conducted using a premixed laminar CH₄/air burner. Laser-induced breakdown was achieved by focusing a 532-nm nanosecond pulse from a Q-switched Nd:YAG laser with an anti-reflection-coated lens. Mixture ignition and the early stages of flame propagation were studied using a high speed Schlieren technique. Despite the stochastic characteristic of the laser breakdown phenomena, good reproducibility in the minimum energy required for the ignition measurements was observed. The cases in which the CH₄/Air mixture flow ignites are defined as those with a laminar flame front propagation visible in the Schlieren images 10 ms after the energy deposition. The same minimum ignition energy (MIE) versus equivalence ratio (Φ) type of curves were obtained with a laser-induced spark and with a spark plug. Due to the threshold of energy required to obtain breakdown and the stochastic character of the energy absorption by the spark, a constant value was obtained (corresponding to the breakdown threshold) when the minimum ignition energy was lower than the breakdown threshold. As already noticed by several authors, MIE values higher than those observed using spark plugs were obtained. However, these differences tended to disappear at the lean and rich fuel limits.     

A multipole expansion-based boundary element method for axisymmetric potential problem

The multipole expansion is an approximation technique used to evaluate the potential field due to sources located in the far field. Based on the multipole expansion, we describe a new technique to calculate the far potential field due to ring sources which are encountered in the boundary element method (BEM) formulation of axisymmetric problems. As the sources in the near field are processed by the slower conventional BEM, it is important to maximize the amount of multipole calculations taking advantage of both interior and exterior multipole expansions. Numerical results are presented for an axisymmetric potential test problem with Neumann and Dirichlet boundary conditions. The complexity of the proposed method remains O(N²), which is equal to that of the conventional BEM. However, the proposed technique coupled with an iterative solver speeds up the solution procedure. The technique is significantly advantageous when medium and large numbers of elements are present in the domain.     

Prediction of the long-term outdoor weathering of poly(vinyl chloride)

The prediction of the long-term durability of PVC polymeric material has been a controversial subject for a long time. Attempts to evaluate this durability have indeed largely preceded experiments on the basic mechanisms of PVC degradation, and they have been essentially empirical. The present paper reports on the general rules that have to be followed to avoid basic errors in predicting the performance of PVC compounds from accelerated weathering experiments.     

Steady flow of liquid aluminum in a rectangular-vertical ingot mold,thermally or electromagnetically activated

Hydrodynamic and thermal fields were studied in liquid aluminum circulating in a specially built parallelepipedic ingot mold. Fluid flow could be produced either by using an electromagnetic linear motor or by natural convection effects. Velocity measurements were performed using a magnetodynamic probe during steady state flow experiments. A theoretical model of heat transfer and fluid flow was developed and used to solve simultaneously Navier-Stokes and energy balance equations. The comparison of theoretical and experimental results is satisfactory regarding general distribution of velocity and temperature. It gives a better understanding of the effects of fluid flow in the melt produced either by external stirring or by natural convection.     

Electromagnetic immunity model of an ADC for microcontroller’s reliability improvement

This paper deals with the study of electromagnetic compatibility prediction of integrated circuits in order to improve their reliability. The study takes place in the context of embedded electronic circuit where the proximity of the analog and digital parts increases. The case of microcontroller is considered and more particularly the susceptibility of the Analog to Digital Converter (ADC) device. The use of the new immunity approach (ICIM-CI model) is proposed to achieve the susceptibility modelling of the ADC. The model is built step by step (functional and coupling path models). Then, it is possible to estimate the effect of disturbances on the sensitive nodes. Finally the aim of EMC circuit compliance is enhanced.