Electronic Sensing of Tastes

Abstract

The taste sensor showed a similar pattern for chemical substances producing the same taste qualities, while quite different patterns were obtained for substances with different taste qualities. In fact, similar outputs were obtained for, e.g., NaCl, KCl and KBr eliciting saltiness, whereas their patterns differed clearly from those for other basic taste qualities. The taste of amino acids was also classied into several groups in accordance with the human taste sense. The taste sensor has a new concept of global selectivity. What is important in recognition of taste is not discrimination of minute difference in molecules but to transform molecular information contained in interactions with biological membranes into several kinds of groups, i.e., taste intensities and qualities. This function is of a high level, where intelligent sensing is required. In this sense, the taste sensor is essentially an intelligent sensor to reproduce the taste sense, which is a complex, comprehensive sense of humans. Several kinds of commercial drinks such as coffee, beer and mineral water were discriminated easily using the taste sensor. The taste sensor has a sensitivity, reproducibility and durability higher than those of humans. Human taste expressions such as ‘bitterness’ and ‘sourness’ were quantied, and also the physico-chemical indices for food production such as alcohol concentration and titratable acidity were shown to be measured by the taste sensor. Improvements in the membranes and measurement methods have also been made for the purpose of measurements, e.g., by adopting the Langmuir�Blodgett method [38], a monolayer of thiol-containing lipids [39] or impedance measurements [40]. The taste sensor will be applicable for quality control in the food industry and will help the automation of production. The sense of taste is vague and largely depends on subjective factors of human feelings. If we compare the standard index measured by means of the taste sensor with sensory evaluation, we will be able to assess taste objectively. Moreover, the mechanism of information processing of taste in the brain as well as the reception at taste cells will also be claried by developing a taste sensor which has output similar to that of the biological gustatory system. In fact, a recent study [19] has shown that astringency is a taste expressed by bitterness and sourness, whereas astringency has so far been considered not as a taste sense but a tactile sense. The result using the taste sensor indicates that the reception mechanism of taste substances in biological systems should be reconsidered. Objective scales of physical quantities such as length and time were proposed over two thousand years ago. We are now familiar with quantitative, objective scales, although there exists subjective feeling as well. As for taste, however, we have had no scale so far. The taste sensor provides a quantitative, objective measure of taste. ‘Deliciousness’ will be measured simultaneously using other sensors. Excellent odor or gas sensing systems based on various principles have also been developed [41—47]. We are now standing on the threshold of a new age of food culture.