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Acoustic waves could be "electronic tongue" for flavour tests

By Stephen Daniells , 25-Jul-2006

Fundamental research from a UK-US collaboration could lead to development of a small, robust, low power flavour tester that can not only distinguish between the four basic tastes, but also umami and metallic.

Such a development has implications for both the food and beverage industries under increasing pressure to develop novel flavours that are readily accepted by ever-demanding consumers.

The new sensor, which uses surface acoustic wave (SAW) sensors, could "offer robust, low-cost screening of certain liquids and thus commercial application" say the researchers, and offer a replacement to bulkier devices.

"Human sensory tests are regularly employed in the food and beverages industries, but results are based on subjective judgements and variations between panels can be up to 50 per cent in terms of flavour units. Therefore, the development of 'objective' tools to detect taste is very much needed," said the researchers, lead by Marina Cole from the University of Warwick.

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.

The Warwick scientists, in collaboration with Peter Hesketh at the Georgia Institute of Technology, have investigated the use of shear-horizontal surface acoustic wave (SH-SAW) microsensors to analyse the four basic tastes of saltiness, sweetness, sourness, and bitterness, as well as the more complicated tastes of umami and metallic.

The technique is based on the principle that different tastes affect both the amplitude (size) and phase of the acoustic waves, allowing the scientists to use sound to gauge tastes based on physical measurements rather than the electrochemical interactions used by other sensors.

The engineers developed a system to introduce samples into the active sensing area using a low-cost flow system, creating a fully automated measurement system. The acoustic wave is emitted at a frequency of 433 MHz and picked up by SH-SAW microsensors.

"Results show that good discrimination between the different taste samples is possible," wrote the authors in the peer-reviewed journal Sensors and Actuators B: Chemical (doi: 10.1016/j.snb.2006.04.040).

Not content to be able to distinguish the four basic taste as well as umami and metallic, the researchers also performed preliminary tests to separate samples within the same taste family, such as caffeine an two different quinine solutions from the bitter taste family.

"These preliminary tests suggest that it is possible to discriminate between samples with various concentrations," they said.

This fundamental research needs significant further investigation, but the researchers concluded: "Initial results are encouraging and applications are envisaged for the rapid, low-cost (and, possibly, wireless) screening of liquid samples in the food and beverage industries."

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.

The development of electronic sensors is not exclusive to "electronic tongues" with the food industry gradually starting to use e-noses ("electronic noses") as part of the quality supply chain to reduce costs.

In 2004 researchers at Cranfield University in the UK reported they had come up with an e-nose for the early detection of 'undesirable off-odours and microbial contaminants' in dairy and bakery products. The EU-funded project, led by Professor Naresh Magan, found the new technology can be used to quickly detect bacteria, yeasts, filamentous fungi and off-odours.

Based on conducting polymer sensor arrays or metal oxide sensor arrays the researchers claim the nose offers rapid and early cost effective' detection of undesirable, harmful contaminants, toxins and taints.

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