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The 17th (2017) Yamazaki-Teiichi Prize Winner Measurement Science & Technology

Research and development of the taste sensor

winner Winner
Kiyoshi Toko
History
Mar. 1975 Graduated from Department of Electrical Engineering, Faculty of Engineering, Kyushu University
Mar. 1980 Completed Doctoral Program in Electrical Engineering, Graduate School of Engineering, Kyushu University
Apr. 1980 Assistant, Department of Electrical Engineering, Faculty of Engineering, Kyushu University
Jul. 1990 Associate professor, Department of Electrical Engineering, Faculty of Engineering, Kyushu University
Apr. 1997 Professor, Graduate School of Information Science and Electrical Engineering, Kyushu University
Nov. 2013 Director, Research and Development Center for Taste and Odor Sensing
Present

winner Winner
Hidekazu Ikezaki
History
Mar. 1986 Completed Masters Program, Graduate School of Electrical Engineering, Graduate School of Science and Engineering, Waseda University
Apr. 1986 Entered Anritsu Corporation
Jan. 2002 Established Intelligent Sensor Technology, Inc., Senior Management Director
Mar. 2005 President, Intelligent Sensor Technology, Inc.
Present

Reason for award

Kiyoshi Toko has constructed sensors that selectively respond to taste qualities corresponding to the principal axes of human gustatory senses, i.e., sweetness, saltiness, sourness, bitterness, and umami, by sensing an electrical-potential difference across an artificial lipid⁄polymer membrane. He realized the worlds first sensing system that quantifies taste. In collaboration with Hidekazu Ikezaki, Dr.Toko developed and put into practical use a taste-sensing system that senses the principal axis and processes signals. Over 400 units of the device, which recognizes and displays taste, have been sold domestically and abroad. The taste that humans sense is a mixture of tastes from the principle axes. To convey this mixed taste not as a numerical value, but as an intuitively perceivable representation, a radar chart relating to several principal axes is made, or two principal axes expressing characteristics are selected, the taste being displayed as points on the plane that these axes create. Since the food industry has conventionally depended on human senses, unstable elements have remained in the management of manufacturing processes and quality control. Introduction of the taste recognition system could eliminate quality fluctuations. The taste sensing system also enables us not only to design new tastes in accordance with variance in consumer preference with the times and generations, as well as varying from region to region, but also to develop new products that suit their tastes. Dr.Toko and Dr.Ikezaki have established the worlds first quantitative taste measurement method, and they have created a device based on it that has spread throughout society, greatly contributing to quality control and objectivization of product characteristics in the food industry.
Based on the above considerations, Dr.Toko and Dr.Ikezaki have been awarded the 17th Yamazaki-Teiichi Prize in Measurement Science & Technology.

Background of research and development

Toko, who served as an assistant at Kyushu University, began research and development of this award-winning "taste sensor" in 1985. At that time, gustatory sensors (or taste sensors) were undeveloped. In Toko's research, artificial lipid membranes mimicking living organisms were utilized as the receptor part of the taste sensor. Previously, electric conductivity meters had been used to measure saltiness, refractometers to measure sweetness, and pH meters to measure sourness. However, it cannot be said that they measure "taste" for the following reasons: Calcium, which contributes to bitterness, also affects electric conductivity, making saltiness measured by this method inaccurate. Furthermore, any non-sugar substances with large molecular weight will change the refractive index, making refractometer measurements of sweetness inaccurate. It is also known that there is no direct relation between pH and sourness in, for example, sake. Of course, if the substances to be measured are always in the same category, these methods are effective; however, it is impossible to apply them to general foods because we do not know the exact ingredients of what we eat every day, that is, foods in a normal situation.
Furthermore, it was known that there are interactions between the basic tastes (saltiness, sweetness, sourness, bitterness, and umami). For example, if sweet sugar is added to bitter foods, it will be found that not only does sweetness increase, but bitterness decreases. This is a suppression effect. When inosinic acid, the umami taste substance in meat, is added to sodium glutamate, another umami taste substance, the umami taste dramatically increases, which is a synergistic effect. These interactions could not be reproduced at all with conventional methods. Even if analytical equipment, such as gas chromatography, is used to quantify chemical substances contained in foods, it is impossible to know the taste of the foods from the results because we do not know the contributions or interactions of the hundreds of chemical substances contained in foods to the taste.
Under such circumstances, in the food and pharmaceutical industries, evaluation of taste depended on a sensory test (taste test), which was inevitably subjective and ambiguous. As such, the advent of scientific technology that enables us to evaluate taste objectively and quantitatively has been eagerly awaited. Toko succeeded in prototyping the taste sensor in 1989. Eight kinds of lipid⁄polymer membranes with different properties are used in the receptor of this sensor. The membranes are formed by blending lipids with plasticizers (that is, polymers). In this system, a different sensor output for each taste quality is obtained from these membranes, and the taste is comprehensively evaluated based on the differences in the potential output. This system shows good correlation with the sensory test on the five basic tastes, and interactions between tastes can also be detected. This is the birth of the "multichannel taste sensor.

Achievements

Toko has been involved in broad academic collaborative research with Anritsu Corporation since 1986. Full-scale collaborative research with Ikezaki of Anritsu began in 1988. In 1989, a patent on the multichannel taste sensor was filed jointly with Anritsu, and an article was published in an international journal in 1990.
Since then, Toko and Ikezaki have worked cooperatively. Ikezaki established Intelligent Sensor Technology, Inc. (INSENT), specializing in the development, manufacture, and sale of the taste sensors, in 2002. Taste & Aroma Strategic Research Institute Co. Ltd. was established with investment from Sougou Shoken Co., Ltd., Sapporo, in 2004. This company is engaged in providing the taste database using the taste sensor.
Since applying for the patent, Toko has been involved in fundamental research, such as elucidation of response mechanism, development of a sweetness sensor (measurement of sweetness was unsatisfactory at the time of patent application in 1989), and development of a portable taste sensor. Ikezaki has been engaged in on-site research and development, such as developing and marketing the devices (models SA 401, SA 402, SA 402 B, and TS 5000 Z), and refining them in response to user feedback. Meanwhile, the sweetness sensor technology developed at Kyushu University was transferred to INSENT and put into practical use. The challenges in the taste sensor development were immediately set as the research subject of Kyushu University, indicating the construction of the strong collaboration system for basics, applications, and practical utilization between them. With the support of JST, INSENT succeeded in developing receptor membranes responsive to each taste quality. This was a splendid example of industry-academia-government collaboration.
Toko and Ikezaki proposed the world's first taste measurement system, spread it globally as a device, and brought innovation to the food and pharmaceutical industries.


Meaning of the achievements

Currently, the taste sensor is utilized in over 400 companies, public institutions, universities, etc. With this taste sensor, it is possible to show the taste of foods in a taste map (map of taste) or radar chart composed of the basic tastes. The taste sensor successfully brought the taste sensed by the tongue to the world seen by the eyes." This is advent of the worlds first "scale of taste." Invention and research of this taste sensor in Japan have prompted western countries to focus on research and development of electronic tongues.
In this globalized IoT era, the importance of the taste sensor is increasing more and more. A desired taste is created using AI and transmitted beyond the time and space. In the global development of foods, the characteristics of foods in each region are grasped by the taste sensor in advance. The taste sensor is now on the cusp of utilization in multiple, diverse aspects: search for a favorite taste using smartphones or tablets that register the taste data, production of foods with stable quality, manufacture of non-bitter medicines, and production of sweet foods with reduced calorie content or salty foods with reduced salt. In these days when many countries are facing the serious concerns of rapid aging and very low birthrate, the utilization value of the taste sensor will increase more and more.

Taste sensor and electrode commercially available now (Taste detection device TS-5000Z: manufactured by INSENT)th=
Fig. Taste sensor and electrode commercially available now (Taste sensing system TS-5000Z: manufactured by INSENT)


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