Electronic Tongues and Combinations of Artificial Senses

The technique of electronic tongues or taste sensors has developed very fast during the last years due to its large potential, and the interest for the concept is steadily increasing. In principle, they function in the same way as the electronic nose, but are used in the aqueous phase. In this article, the technique as such is described, as well as different types of electronic tongues, based on potentiometry or voltametry. Also the combination of different artificial senses is discussed. Different sensing principles can be used in electronic tongues or taste sensors, such as electrochemical methods like potentiometry or voltametry, optical methods or measurements of mass changes based on e.g. quartz crystals. The first concept of an electronic tongue or taste sensor was based on ion sensitive lipid membranes and developed to response to the basic tastes of the tongue, that is sour, sweet, bitter, salt and “umami”. It has been further developed and is commercialized. The detecting part is an eight-channel multi sensor, placed on a robot arm and controlled by a computer. This taste sensing system has mainly dealt with discrimination and estimation of the taste of different drinks. An electronic tongue, based on potentiometric sensor arrays of two general kinds, conventionally ones such as pH, sodium and potassium selective electrodes, and specially designed ones, has also been described. This system has been used for recognition of different kinds of drinks such as tea, soft drinks, juices and beers and compounds of relevance for pollution monitoring in river water. The use of voltametry as sensing principle in an electronic tongue has also been developed. This electronic tongue consists of a number of working electrodes made of different materials, a reference electrode and an auxiliary electrode. Different types of pulsed voltametry were applied. Application examples include classification of fruit juices, test for bacterial growth in milk or water quality. A hybrid electronic tongue has also been developed, based on the combination of the measurement techniques potentiometry, voltametry and conductivity. By using a combination of different artificial senses, the analytical capability will be considerably increased. Thus, the combination of an electronic tongue and an electronic nose for classification of different fruit juices was investigated. Furthermore, a special “artificial mouth” or “crush chamber” has been designed, in which information corresponding to three senses could be obtained — “auditory” by a microphone, “tactile” by a force sensor and “olfaction” by a gas sensor array, thus collecting information mimicking these three human sense. In this artificial mouth crispy products could be crushed under controlled conditions to make a complete sensory evaluation, all five human senses are involved. A new approach for the assessment of human based quality evaluation has been obtained by the design of an electronic sensor head. In this system, the artificial analogues to all the five human senses are used for quality evaluation of a sample could be collected.