Electronic tongue

The electronic tongue is an instrument that measures and compares tastes.

Chemical compounds responsible for taste are detected by human taste receptors, and the seven sensors of electronic instruments detect the same dissolved organic and inorganic compounds. Like human receptors, each sensor has a spectrum of reactions different from the other. The information given by each sensor is complementary and the combination of all sensors' results generates a unique fingerprint. Most of the detection thresholds of sensors are similar to or better than those of human receptors.

In the biological mechanism, taste signals are transducted by nerves in the brain into electric signals. E-tongue sensors process is similar: they generate electric signals as potentiometric variations.

Taste quality perception and recognition is based on building or recognition of activated sensory nerve patterns by the brain and on the taste fingerprint of the product. This step is achieved by the e-tongue’s statistical software which interprets the sensor data into taste patterns.

One variation was developed by Professor Fredrik Winquist of Linköping University, Sweden.^[1]

Operation

Liquid samples are directly analyzed without any preparation, whereas solids require a preliminary dissolution before measurement. Reference electrode and sensors are dipped in a beaker containing a test solution. A voltage is applied between each sensor and a reference electrode, and a measurable current response results that is consistent with the Cottrell equation. This current response is a result of oxidizing reactions that take place in the solution due to the voltage difference, and can be amplified through catalytic surface treatments. The response is measured and recorded by the e-tongue's software. These data represent the input for mathematical treatment that will deliver results.

Applications

Electronic tongues have several applications in various industrial areas: the pharmaceutical industry, food and beverage sector, etc. It can be used to:

• analyze flavor ageing in beverages (for instance fruit juice, alcoholic or non alcoholic drinks, flavored milks…)
• quantify bitterness or “spicy level” of drinks or dissolved compounds (e.g. bitterness measurement and prediction of teas)
• quantify taste masking efficiency of formulations (tablets, syrups, powders, capsules, lozenges…)
• analyze medicines stability in terms of taste
• benchmark target products
• monitor environmental parameters
• monitor biological and biochemical processes

Artificial taste

The electronic tongue uses taste sensors to receive information from chemicals on the tongue and send it to a pattern recognition system. The result is the detection of the tastes that compose the human palate. The types of taste that is generated is divided into five categories sourness, saltiness, bitterness, sweetness, and umami (savoriness). Sourness, which includes hydrogen chloride, acetic acid, and citric acid, is created by hydrogen ions. Saltiness is registered as sodium chloride, sweetness by sugars, bitterness, which includes chemicals such as quinine and caffeine is detected through magnesium chloride,and umami by monosodium glutamate from seaweed, or disodium guanylate in meat/fish/mushrooms.

See also

• Electronic nose
• Chemical field-effect transistor
• Chemiresistor
• Gustation
• Metal oxide sensors

References