J.A. de Saja

Combination of an e-nose, an e-tongue and an e-eye for the characterisation of olive oils with different degree of bitterness.

An electronic panel has been used to characterise the organoleptic characteristics of twenty-five extra virgin olive oils from varieties Hojiblanca, Picual and Arbequina, with different degree of bitterness. The method consists in the combination of three systems: electronic nose, electronic tongue and electronic eye. The Principal Component Analysis (PCA), where PC1, PC2 and PC3 explained 59% of the total variance between the samples, has demonstrated that the capability of discrimination of the combined system is superior to that obtained with the three instruments separately. This improvement is due to the increased information extracted from each sample. Partial Least Squares-Discriminant Analysis (PLS-DA) has allowed separation of the groups in function of olive variety with a root mean square error of prediction (RMSEP) lower than 0.099. Using PLS1 and PLS2 regression models, good correlations have been found between the signals obtained from the electronic tongue and the polyphenolic content (measured by chromatographic methods) or the bitterness index (scored by a panel of experts) with correlation coefficients higher than 0.9 in calibration and validation. These preliminary results indicate that the combination of an e-nose, an e-tongue and an e-eye can be a useful tool for the analysis of olive oil bitterness.

CRYSTALLIZATION BEHAVIOR OF POLYPROPYLENE FILLED WITH SURFACE-MODIFIED TALC

Talc-filled polypropylene (PP) composites were prepared by extrusion in a wide composition range (0–40 wt %). To improve the affinity relation between talc and the PP matrix, we modified the talc surface with silane coupling agents. Differential scanning calorimetry investigations on test samples, prepared by injection moulding, revealed that the talc content and its surface modification had a pronounced effect on the crystallization behavior of the filled PP composites. The experimental results indicate that a talc concentration of 2 wt % strongly affects the nonisothermal crystallization process of the PP, especially when talc is silane treated Isothermal crystallization experiments on samples with minimum amounts of talc (2 wt %) revealed an improved nucleation activity with silane-treated talc.

CONSTRAINED CRYSTALLIZATION AND ACTIVITY OF FILLER IN SURFACE MODIFIED TALC POLYPROPYLENE COMPOSITES

Abstract Two different series of talc-polypropylene composites ranged between 0 and 40 wt % were prepared by extrusion. In one of the series, the talc surface was modified with silane coupling agents in order to improve the affinity relation between the filler and the PP matrix. By means of X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) techniques, the configuration of the PP crystalline phase and the nucleating activity of the mineral have been stated in both series.

Langmuir-Blodgett film and carbon paste electrodes based on phthalocyanines as sensing units for taste

Abstract In this work, the possibility of using voltammetric electrodes based on phthalocyanine compounds as the sensing units of an electronic tongue has been investigated. Sensors based on monophthalocyanines (including cobalt and copper phthalocyanines) and lanthanide bisphthalocyanines (comprising europium, gadolinium and lutetium bisphthalocyanines and the octa- tert butyl substituted praseodymium bisphthalocyanine) have been prepared using two different methods: the Langmuir–Blodgett (LB) technique and the carbon paste electrode (CPE) technique. The sensors have been used to evaluate the five types of basic tastes (sweet, bitter, salty, acid and umami). Each phthalocyanine shows a characteristic electrochemical response for the solutions investigated. The electrochemical response towards the five basic types of flavours is particularly rich in the case of the bisphthalocyanine compounds. The responses of the sensors prepared using the LB technique has been compared with that of the sensing units prepared by the CPE technique. The response of both types of electrodes is similar, but in the case of the LB films the peaks are better resolved, and the electrodes show a very good repeatability. Nevertheless, their reproducibility is lower than for the CPE electrodes. The electrochemical studies indicate that the charge transport in both types of electrodes is diffusion controlled. A multichannel taste sensor has been constructed using those sensors with the best performances. The array of sensors has been exposed to solutions of the five basic flavours. The principal component analysis (PCA) of the obtained signals has allowed the discrimination of basic tastes.

Dynamic mechanical analysis of injection-moulded discs of polypropylene and untreated and silane-treated talc-filled polypropylene composites

Abstract Dynamic mechanical analysis (DMA) is used to study the dynamic mechanical properties of injection-moulded discs of polypropylene, talc-filled polypropylene composites and silane-treated talc-filled polypropylene composites. Silane addition in a very low proportion improves the adhesion between the filler and the polymer and enables composites to be used where otherwise they could not. Therefore, on the one hand, the composites have different properties due to the filler and the coupling agent, and on the other hand the injection processing induces a structure, resulting in inhomogeneity and anisotropy for the moulded discs. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) techniques are used to help state the microscopic structure and justify the macroscopic properties measured with DMA.

Array of sensors based on conducting polymers for the quality control of the aroma of the virgin olive oil

Abstract In this paper, a sensor array based on thin films of conducting polymers aiming to discriminate among different virgin olive oils is described. The array has been constructed using eight polymeric sensors. They were deposited electrochemically by using different electrodeposition conditions, different monomers (3-methylthiophene, pyrrole and aniline) and doping agents. Olive oil samples with well-defined organoleptic characteristics have been selected by a panel of experts. They included virgin olive oils of different qualities (extra virgin, virgin and lampante) as well as a refined olive oil. Four types of olive oil samples with well-defined “off odours”, that is with unpleasant aromatic notes, named musty, rancid, fusty and muddy, have also been included in the study. The sensors are stable and show good reproducibility and reversibility when exposed to the headspace of the virgin olive oils. The array of sensors combined with a Principal Component Analysis (PCA) allows the discrimination of different types of olive oils.

Discrimination of wine aroma using an array of conducting polymer sensors in conjunction with solid-phase micro-extraction (SPME) technique

Abstract A set of 12 polymeric sensors has been tested as an artificial olfactory system for the identification of wines. Three white and two red Spanish wines produced in different locations where analysed by using two alternative sampling methods. A commercial headspace sampler was not successful in concentrating the specific odorants of the different wines, whereas the solid-phase micro-extraction (SPME) technique led to some promising results. By using a selective SPME-fibre, principal component analysis of the data allowed a clear discrimination of the aromas, even for wines that had very similar organoleptic characteristics.

Array of conducting polymer sensors for the characterisation of wines

The response of an array of polymeric sensors to different Spanish wine varieties has been evaluated. Two different systems for the injection of the volatile compounds, based on static and dynamic headspace sampling, were used. A comparative study of the operation of the array when using one or the other methodology has been carried out. The cross sensitivity of the polymeric films to moisture and ethanol has been explicitly considered. The discrimination and classification capabilities of the sensor array have been examined by statistical analysis of the obtained data using pattern recognition techniques.

Biomimetic biosensor based on lipidic layers containing tyrosinase and lutetium bisphthalocyanine for the detection of antioxidants

This paper describes the preparation of a biomimetic Langmuir-Blodgett film of tyrosinase incorporated in a lipidic layer and the use of lutetium bisphthalocyanine as an electron mediator for the voltammetric detection of phenol derivatives, which include one monophenol (vanillic acid), two diphenols (catechol and caffeic acid) and two triphenols (gallic acid and pyrogallol). The first redox process of the voltammetric responses is associated with the reduction of the enzymatically formed o-quinone and is favoured by the lutetium bisphthalocyanine because significant signal amplification is observed, while the second is associated with the electrochemical oxidation of the antioxidant and occurs at lower potentials in the presence of an electron mediator. The biosensor shows low detection limit (1.98×10(-6)-27.49×10(-6) M), good reproducibility, and high affinity to antioxidants (K(M) in the range of 62.31-144.87 μM). The excellent functionality of the enzyme obtained using a biomimetic immobilisation method, the selectivity afforded by enzyme catalysis, the signal enhancement caused by the lutetium bisphthalocyanine mediator and the increased selectivity of the curves due to the occurrence of two redox processes make these sensors exceptionally suitable for the detection of phenolic compounds.

Prediction of the radiation term in the thermal conductivity of crosslinked closed cell polyolefin foams

The thermal conductivity and the cellular structure as well as the matrix polymer morphology of a collection of chemically crosslinked low-density closed cell polyolefin foams, manufactured by a high-pressure nitrogen gas solution process, have been studied. With the aid of a useful theoretical model, the relative contribution of each heat-transfer mechanism (conduction through the gas and solid phases and thermal radiation) has been evaluated. The thermal radiation can be calculated by using a theoretical model, which takes into account the dependence of this heat-transfer mechanism with cell size, foam thickness, chemical composition, and matrix polymer morphology. A simple equation, which can be used to predict the thermal conductivity of a given material, is presented.