2.3. Electronic tongue measurements

All samples were measured using the ASTREE electronic tongue (Alpha M. O. S., Toulouse, France) multisensory system equipped with an advanced chemometrics software package, and a 48‐position auto‐sampler (Metrohm, Ltd.). The electronic tongue used in this work comprised of seven chemical sensors. The taste sensor set consisted of UMS, SRS, SWS, STS, BRS, SPS, and GPS sensors to detect five basic tastes (umami, sourness, sweetness, saltiness, and bitterness) using an Ag/AgCl reference electrode (Metrohm, Ltd.) (Kang et al., ²⁰¹⁴).

To achieve the best performance of the electronic tongue, the sensors were conditioned by a conditioning, calibration, and diagnostic process before analyzing each sample. 0.01 mol/L of sodium chloride (NaCl), sodium L‐glutamate (MSG), and hydrochloric acid (HCl) were used for the conditioning, diagnosis, and calibration processes (Yang et al., ²⁰¹³). The E‐tongue detecting conditions were set the same as the sensory evaluation method. Distilled water was used for cleaning during the testing. The conditioning test was used for regenerating the activity of sensor coating. The calibration was applied to standardize the sensor values in each analysis and ensure the results of all the samples were consistently and comparably (Campos et al., ²⁰¹²; Ciosek & Wróblewski, ²⁰⁰⁷). A diagnostic process was performed to measure the sensitivity and discriminating capability of the sensor.

All samples were analyzed at ambient temperature with a 10 s measurement time (20 ml volume) and 120 s rinse time for the reference electrode and seven sensors. A washable cycle was performed to clean the sensors before the next analysis (Tian et al., ²⁰¹³). Each sample was measured six times by the sensors, and three stable equilibrium data points were recorded. All the experiments were completed continuously to avoid inconsistency caused by the aging degradation of sensors. Data acquisition and analysis were operated by software Astree II (Alpha M. O. S. V12.0).