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What is a sensor?

Sensors are devices that receive stimuli commonly detected by the five senses of sight, hearing, touch, smell and taste. They can be categorized into two types: physical sensors and chemical sensors. A physical sensor is a device that detects physical quantities, including light, pressure and sound. They have been in use for many years because they are based on relatively simple principles. In contrast, a chemical sensor is a device that detects chemical substances and represents a certain quality. For example, a pH meter is a chemical sensor that responds only to protons, and therefore it high selectivity. However, because there are thousands of taste substances, high selectivity to a single tastant is inappropriate for a taste sensor.


Response principle

A taste sensor is required to exhibit global selectivity so that it responds consistently to the same taste similarly to the human tongue. After years of research with Prof. Toko's group at Kyushu University, Japan, we have successfully developed taste sensors based on an artificial lipid membrane that consistently responds to similar taste. Figure 1 shows the response principle of taste sensors.

Figure 1. Response principle of taste sensors
The lipid in the taste sensor interacts with various taste materials via electrostatic and hydrophobic interactions, which causes a change in potential of the lipid membrane. The change is detected by a computer to provide a sensor output.


Measurement procedure

Figure 2 shows the measurement procedure, which is called the CPA measurement method, used to monitor changes in the membrane potential over time.

Figure 2. Measurement procedure
Process 1: First, the taste sensor is immersed in a reference solution of 30 mM KCl and 0.3 mM tartaric acid to obtain the membrane potential, Vr. The reference solution has almost no taste and is used in this system as an alternative to human saliva.

Process 2: Second, the taste sensor is immersed in the sample solution to obtain the potential, Vs. The difference in potential (Vs – Vr), called the relative value, should approximate the initial taste upon sensory evaluation, including its sourness and saltiness.

Process 3: Third, the taste sensor is rinsed lightly with the reference solution.

Process 4: After rinsing, it is immersed in the reference solution again to obtain the potential, Vr’. The difference in potential (Vr’ – Vr), called the CPA (change of membrane potential caused by adsorption), provides data on the adsorption of bitter and astringent substances.

Process 5: Finally, the taste sensor is rinsed well in alcohol solution to remove adsorbed substances from the membrane before the next sample is measured.


Taste sensors and taste information

Each taste sensor developed by our specific and innovative technologies has global selectivity to a taste quality, so sensor outputs can be converted to taste information that helps distinguish differences in both taste quality and intensity between samples. Table 1 shows the list of taste sensors and the related taste information.
Table 1. Taste sensors and the related taste information
Taste information Sensor Characteristic Targets
Initial taste
(Relative value)
Sourness CA0 sourness produced by citric acid and tartaric acid beer, coffee
Saltiness CT0 saltiness evoked by dietary salts soy sauce, soup, stock sauce
Umami AAE umami (savoriness) by amino acids and nucleic acids soup, stock sauce, meat
Acidic bitterness C00 bitterness derived by bitter substances found in foodstuffs and beverages, but can also be perceived richness with its concentration being low bean curd, stock sauce, soup
Astringency AE1 pungent taste by astringent taste materials wine, tea
Sweetness GL1 sweetness produced by sugars and sugar alcohols sweets, drink
Aftertaste
(CPA value)
Aftertaste from acidic bitterness C00 aftertaste by bitter taste materials beer, coffee
Aftertaste from astringency AE1 aftertaste by astringent taste materials wine, tea
Richness AAE richness, also called “continuity,” evoked by umami substances soup, stock sauce, meat
Aftertaste from basic bitterness AC0
AN0
bitterness of medicines basic drugs (such as quinine hydrochloride, famotidine)
Aftertaste from hydrochloride salts BT0 bitterness of medicines hydrochloride drugs


Application data

The taste sensors developed by INSENT has many applications for foods, beverages and pharmaceuticals.

Radar chart for beer

Radar chart for soy sauce
* Aftertaste-A; Aftertaste from astringency, Aftertaste-B; Aftertaste from acidic bitterness

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