A Taste Sensor Array Based on Polyaniline Nanofibers for Orange Juice Quality Assessment

In this work nanostructured ultrathin films of polyaniline nanofibers deposited by self-assembly and casting onto interdigital microelectrodes were used as efficient sensoactive layers in taste sensors for quality assessment of commercial and freshly squeezed orange juices. Capacitance measurements were carried out to analyze aqueous solutions of citric acid and eight types of orange juices, including four commercial brands of ready-to-drink juice, two commercial brands of artificially reconstituted juices and freshly squeezed orange juices from sweet lime (Citrus limettioides Tanaka) and ‘Pera’ sweet orange (Citrus sinensis (L.) Osbeck). Sensor ability in classifying the juices, i.e., separating different types and grouping similar ones, as well as the possibility of monitoring the aging process as a function of the storage conditions were successfully tested. Results showed that the sensor array was able to detect changes in citric acid concentration down to values as low as 2 ppm. It was also observed that the sensitivity of sensors based on self-assembled films was slightly lower than for cast ones. However, the increase in capacitance with increasing analyte concentration was more regular and the time required for sensor response to return to its baseline was faster for self-assembled films as a consequence of the film regularity in architecture. The sensor array could not only discriminate the different orange juices but also detect the degradation process differentiating the influence of storage conditions in this process, therefore showing that this sensor array presents a great potential to be used for quality monitoring of orange juices.