MICROFLUIDIC ELECTRONIC TONGUE FOR SCREENING GRAPE JUICE-BASED BEVERAGES WITH DIFFERENT BIOACTIVE COMPOUND CONTENTS

Beverage classification and authentication are among the major challenges faced by regulatory agencies. For grape juice-based beverages, the commercial categories are defined by the minimum juice content, which affects their commercial value and bioactive compound content. The determination of these compounds relies on chemical analyses that involve concentrated acids and generate waste. Considering the demand for green analytical chemistry, the impedimetric electronic tongue (e-tongue) emerges as an alternative, as it provides global responses without reagents and with minimal sample preparation. This study aimed to evaluate the discrimination of grape juice beverages by a microfluidic impedimetric e-tongue and its association with anthocyanin and phenolic compound contents. Five beverages were evaluated: juice obtained by crushing fresh grapes and four commercial beverages (industrial juice, mixed grape and apple juice, nectar and low-juice grape drink). Samples were centrifuged, and the same supernatant was used in the e-tongue, without dilution, and in the reference analyses. The e-tongue consisted of four gold interdigitated electrodes, one uncoated and three coated by the layer-by-layer technique with different polyelectrolyte films, with or without silver or gold nanoparticles, integrated into a microfluidic channel. Impedance signal (10 Hz to 1 MHz, 25 mV) were acquired with an LCR meter in six replicates. The impedance magnitude at 1 kHz was autoscaled and subjected to principal component analysis (PCA) using the PLS_Toolbox tool (MATLAB). Total monomeric anthocyanins (TMA) and total phenolic content (TPC) were determined in triplicate by the pH-differential and Folin-Ciocalteu methods, respectively. The results showed that impedance decreased with increasing juice content in the beverage. The first two PCs explained 99.97% of the variance. PC1 (96.21%) was related to grape juice content of the samples, with lower impedance in beverages with a higher proportion of juice. TMA ranged from 1.4 to 107.7 mg/L and TPC from 405 to 1,896 mg GAE/L. An inverse relationship was observed between impedance and TMA. The same behavior was not observed for TPC, where the mixed juice exceeded the fresh fruit juice sample, probably due to the contribution of apple phenolics, and the nectar and low-juice grape drink showed similar values, whereas the e-tongue discriminated these beverages based on the global composition of the matrix. The fresh and industrial juices, both 100% grape, were clustered together in the negative region of PC1 in the score plot, consistent with their category. However, the e-tongue did not distinguish them despite a 3.7-fold difference in TMA, suggesting that signal is mainly governed by the ionic content rather than by anthocyanins. Further confirmation of the possible correlations observed requires additional investigation with a more robust sample set. Nevertheless, the results indicate the potential of the e-tongue fingerprint to discriminate different categories of grape-based beverages without the use of chemical reagents.