# Electronic Sensing Technologies in Food Quality Assessment: A Comprehensive Literature Review
## 5 e-Tongue  
E-tongues are analytical devices designed to recognize and classify the various flavors of chemicals present in food liquids or samples. They operate on principles similar to the human sense of taste, employing sensors. These devices can evaluate multi-component mixtures regarding quality and quantity, which is why they are becoming increasingly prominent in food analysis [116; 140]. The primary objective of e-tongue technology is to analyze food samples using a set of sensors, such as ion-selective electrodes with specific properties, and to perform statistical analyses on the data collected. e-Tongues can describe the taste profiles of complex liquids or food samples converted to liquid form. This technology can provide insights into aspects like freshness and ripeness [141; 142]. Examples of e-tongue applications and the results obtained in food quality research are summarized in Table 3. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Device Type/Sensors Used** & **Application** & **Quantitative Metrics** & **References** \\ \hline The sensor set consists of seven different chemical sensors and a reference electrode (Ag/AgCl) & Development of an effective method for identifying spices for instant noodles & In combination with the e-nose, it provides fast, objective, highly automated, and inexpensive food & [86] \\ \hline SA-402B Electronic Tongue (E-tongue) (Intelligent Sensor Technology, Inc., Atsugi, Japan) Sensor array: 6 taste sensors for bitter, umami, sour, asttingent, salty, and sweet; and two reference electrodes & Detection of flavor characteristics of loquat fruit during the post-harvest shelf life (18 days) & Shows changes in sensory taste indices typical of loquats & [97] \\ \hline ASTREE E-tongue (Alpha M.O.S., Toulouse, France); sensor array consists of 7 sensors (AHS, ANS, SCS, CTS, NMS, PKS, and CPS) and a standard reference electrode (Ag/AgCl) & Characterization of the different quality levels of Congolese black tea & A 7-dimensional feature data set (AHS, ANS, SCS, CTS, NMS, PKS, and CPS) was obtained to characterize the flavor quality of the tea infusion & [98] \\ \hline Tongue system, a 6 th generation sensor system consisting of AHS, ANS, SCS, CTS, NMS, PKS, and CPS sensors together with a standard reference electrode (Ag/AgCl), giving a total of 7 sensors & Identifying differences in flavor profiles in different varieties of bee pollen & The basis for comprehensive processing and quality control of bee pollen products & [101] \\ \hline The volumetric e-tongue used in this study consisted of 4 working electrodes (platinum, gold, crystalline carbon, and silver), a reference electrode (Ag/AgCl), and a platinum auxiliary electrode & Distinguishing between different brands of pasteurized milk & Clear differentiation of milk brands on the first day of storage, combined use with e-nose very promising for monitoring milk quality in the dairy industry, mainly where on-line control is needed & [104] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Application and obtained effects of the e-tongue system. The sensors that form the core of the e-tongue system can be categorized into three main types: electrochemical (which includes voltameric, potentiometric, amperometric, impedimetric, and conductometric), optical, and enzymatic (biosensors). Typically, e-tongue systems consist of up to ten sensors, with potentiometric and voltameric sensors being the most common. Volumetric e-tongues are particularly useful for multi-component measurements, such as determining the levels of chlorides, nitrites, and nitrates in meat. However, they are limited to samples that involve oxidation and reduction reactions [6; 51]. e-Tongues utilize various sensors and data processing techniques to analyze complex fluid systems [136]. The electrodes assess the taste or character of a substance by measuring changes in resistance or current between them [71]. Once this information is converted into a digital format, it is input into a mathematical model and evaluated using computer