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'Electronic tongue' could aid sweetened formulations

By Stephen Daniells , 18-Aug-2009

Scientists have developed an ‘electronic tongue on a chip’ to quickly and accurately identifies sweetness, giving manufacturers an inexpensive quality control tool.

The development boasts 100 per cent accuracy over the full range of natural and artificial sweet substances, including 14 common sweeteners, according to findings presented at American Chemical Society's 238th National Meeting.

According to the developers, led by Kenneth Suslick from the University of Illinois at Urbana-Champaign, the “sensory sweet tooth” could be a simple quality control test to ensure a consistent, predictable flavour for soft drinks, beer, and other beverages.

The new sensor, reportedly about the size of a business card, can also identify sweeteners used in solid foods such as cakes, cookies, and chewing gum, said the researchers.

“We take things that smell or taste and convert their chemical properties into a visual image,” said Suslick. “This is the first practical ‘electronic tongue’ sensor that you can simply dip into a sample and identify the source of sweetness based on its colour.”

A brief taster of sensor history

Artificial taste sensors, often refer to as "electronic tongues", can be based on a number of techniques including potentiometry and voltametry, both are electrochemical techniques.

Some scientists have also looked at using acoustic devices, with so-called quartz crystal microbalances (QCM) said to be the first ones used as sensors that work by measuring frequency changes due to mass changing on the device surface.

A couple of years ago, scientists from the University of Surrey in the UK reported the development of a new sensor, which uses surface acoustic wave (SAW) sensors.

However, despite these developments, the team behind the new sensory state that earlier devices generally suffered from a difficulty to distinguish one chemical flavour from another, particularly in a complex mixture.

The new technique uses colorimetric sensor arrays, consisting of a tough, glass-like container with up to 36 tiny printed dye spots. When the chemicals in each spot react with sweet substances a colour change occurs, and these vary with the type and intensity of sweetener present.

According to Suslick and his co-workers, the sensor can distinguish between 14 different natural and artificial sweeteners, including sucrose, xylitol, sorbitol, aspartame, and saccharin.

Furthermore, the new sensor can produce results in about 2 minutes, they said.

“With this device, manufacturers can fix the problem immediately — on location and in real-time,” said Suslick.

The researchers note that more research is needed before the device could be considered a true “electronic tongue”, and be able to detect sweet, sour, salty, bitter, and umami.

The real thing

Previous research into taste has revealed that the human tongue has about 10,000 taste buds with five taste sensations: sweet, bitter, and umami, which work with a signal through a G-protein coupled receptor; salty and sour which work with ion channels.

Contrary to popular understanding, taste is not experienced on different parts of the tongue. Though there are small differences in sensation, which can be measured with highly specific instruments, all taste buds, essentially clusters of 50 to 100 cells, can respond to all types of taste.

Taste buds (or lingual papillae) are small structures on the upper surface of the tongue that provide information about the taste of food being eaten.

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