PubMed · 7630707
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C H Lifschitz. 1995. Fruit juice.. https://pubmed.ncbi.nlm.nih.gov/7630707/
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Pure and composite nanostructured films of conducting polymers were used as individual sensing units constituting an electronic tongue. The use of extremely thin films for signal transduction via impedance spectroscopy measurements in the frequency range 10-1 MHz allows the detection of trace amounts of tastants and inorganic contaminants in liquid systems. In addition, the sensor could detect the suppression of sourness by sweetness displaying similarities with the biological system. Brands of several commercial beverages could be easily distinguished without complex analysis, including the discrimination of waters, tastants and wines.
A procedure for the analysis of the oxygen-18/oxygen-16 isotope ratio of ethanol derived from the sugars of orange juice using the preparation steps of the SNIF-NMR method followed by pyrolysis-isotope ratio mass spectrometry is presented. The isotopic fractionation induced by the isotope effects of fermentation and distillation have been investigated, and it is shown that reproducible results can be obtained when appropriate analytical conditions are used. It is also shown that the oxygen isotope distribution in the water and organic matter pools of fruits remains quite stable during the harvest period and is not altered by the precipitation rate within the last few days before the fruits are picked. Due to the robustness of the method and the fact that most of the oxygen-18 enrichment from the initial sugars is still present in the end-product, ethanol appears as a convenient internal reference to circumvent the spatial and temporal variability observed for the oxygen-18/oxygen-16 isotope ratio of water. A very strong correlation is observed between the isotopic deviations of ethanol and water, which is altered in the event of a water addition, even at a low level. Combining the information brought by these two parameters leads to a more efficient authenticity testing tool, which avoids false positive cases and provides a lower detection limit for added water in juices not made from concentrate, whatever the origin of the sample tested.
Cholinesterase sensors based on screen-printed electrodes modified with polyaniline, 7,7',8,8'-tetracyanoquinodimethane (TCNQ), and Prussian blue have been developed and tested for detection of anticholinesterase pesticides in aqueous solution and in spiked grape juice. The influence of enzyme source and detection mode on biosensor performance was explored. It was shown that modification of the electrodes results in significant improvement of their analytical characteristics for pesticide determination. Thus, the slopes of the calibration curves obtained with modified electrodes were increased twofold and the detection limits of the pesticides were reduced by factors of 1.6 to 1.8 in comparison with the use of unmodified transducers. The biosensors developed make it possible to detect down to 2 x 10(-8) mol L(-1) chloropyrifos-methyl, 5 x 10(-8) mol L(-1) coumaphos, and 8 x 10(-9) mol L(-1) carbofuran in aqueous solution and grape juice. The optimal conditions for grape juice pretreatment were determined to diminish interference from the sample matrix.