Taste sensor output patterns

The DOPH membrane and the ammonium salt membrane responded to taste substances in different ways. The above results suggest that taste substances can be perceived satisfactorily using various kinds of lipid materials. Furthermore, we must improve the sensing reproducibility. As a second step, we have developed a multichannel lipid membrane taste sensor. Taste substances can be discriminated by the output pattern from several lipid membranes. 

The above-mentioned 256 mixed solutions were measured with the multichannel taste sensor. Therefore, data on the output electrical potential pattern were taken for the 256 solutions. While the data on each channel output were dispersed discretely in the four-dimensional space constructed from four different concentrations, we approximated them by a quadratic function of the concentrations. As a result, eight quadratic functions were obtained. The data can be regarded as expressed by a set of eight different functions (corresponding to 8 channels) of concentrations of four taste substances. 

The present sensor could easily discriminate between some kinds of commercial drinks such as coffee, beer and aqueous ionic drinks (Figure 11) [22], Since the standard deviations were 2 mV at maximum in this experimental condition, these three output patterns are definitely different. If the data are accumulated in the computer, any food can be easily discriminated. Furthermore, the taste quality can also be described quantitatively by the method mentioned below. In biological systems, patterns of frequency of nerve excitation may be fed into the brain, and then foods are distinguished and their tastes are recognized [4-8]. Thus, the quality control of foods becomes possible using the taste sensor, which has a mechanism of information processing similar to biological systems. 

The direct transformation from the output pattern to the taste quality was performed here as one trial of expressing the actual human sensation using the output electrical pattern. A similar trial was done for evaluation of the strengths of sourness and saltiness, which will be mentioned later. These two trials depend on the utilization of simple transformation equations by extracting typical properties of output patterns. This method is effective if some data on sensory tests, using humans as a standard, can be obtained to compare with the sensor outputs. However, the expressions for the tastes of beer are obscure because they are not described by the five basic taste qualities. The purpose of the application of the taste sensor is also to express these kinds of obscure terms of human sense in scientific terms. 

The second method to quantify the taste by the sensor may be to extract the characteristics of output patterns by adopting some algebraic functions [19, 20]. We can know the taste quality and estimate the taste strength of test solution by using the functions (Figures 14 and 18). However, it may not be easy to get such reliable, simple functions for expressing the taste strength for each taste quality. 

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