An automated system for the objective evaluation of human gustatory sensitivity using tongue biopotential recordings

The goal of this work is to develop an automatic system for the evaluation of the gustatory sensitivity of patients using an electrophysiological recording of the response of bud cells to taste stimuli. In particular, the study aims to evaluate the effectiveness and limitations of supervised classifiers in the discrimination between subjects belonging to the three 6-n-propylthiouracil (PROP) taster categories (supertasters, medium tasters, and non-tasters), exploiting features extracted from electrophysiological recordings of the tongue. Thirty-nine subjects (equally divided into the three PROP status classes by standard non-objective scaling methods) underwent a non-invasive, differential, biopotential recording of their tongues during stimulation with PROP by using a custom-made, flexible, silver electrode. Two different classifiers were trained to recognize up to seven different features extracted from the recorded depolarization signal. The classification results indicate that the identified set of features allows to distinguish between PROP tasters and non-tasters (average accuracy of 80% ± 18% and up to 94% ± 15% when only supertasters and non-tasters are considered), but medium tasters were difficult to identify. However, these apparent classification errors are related to uncertainty in the labeling procedures, which are based on non-objective tests, in which the subjects provided borderline evaluations. Thus, using the proposed method, it is possible, for the first time, to automatically achieve objective PROP taster status identification with high accuracy. The simplicity of the recording technique allows for easy reproduction of the experimental setting; thus the technique can be used in future studies to evaluate other gustatory stimuli. The proposed approach represents the first objective and automatic method to directly measure human gustatory responses and a milestone for physiological taste studies, with applications ranging from basic science to food tasting evaluations.