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Chemical engineering

Virtual savoring

Embrapa develops electronic tongue to monitor quality in the production of drinks and to detect herbicide contamination in water

eduardo cesarEquipment analyzes water contaminated by herbicides used on cropseduardo cesar

Researchers from Embrapa Agricultural Instrumentation have created a more sensitive device than the human tongue for tasting and analyzing drinks. Dubbed the electronic tongue, the equipment is fitted with six sensors that perform a function similar to taste buds, but they are more efficient. The electronic tongue is not only capable of identifying a legitimate Cabernet Sauvignon red wine, but it also manages to detect differences that are almost imperceptible to the human palate, like those that exist between various brands of mineral water. The invention has now been patented by Embrapa and FAPESP and is at the stage of the final touches for industrial use. It should be available on the market in three years.

The application potential is enormous. The equipment may help in environmental control, monitoring the levels of heavy metals and pesticides contamination in rivers and water springs, and, in basic sanitation, controlling the quality of the water at the treatment stations. In the food industry, the electronic tongue may help to increase rigor in quality control in beverage manufacturing, through continuous monitoring. For the time being, the equipment is fit for operating with wine, coffee and mineral water, but the researchers are now developing sensors for analyzing milk, grape juice and orange juice. In the pharmaceutical industry, the electronic tongue can be used to test drugs and to improve the flavor of bitter medicines.

According to the literature on the subject, this is the first electronic tongue on the basis of conductive polymers in the world. The result of six years of multidisciplinary work that received the support of physicists and materials, mechanical, electronic and electrical engineers from Embrapa, in São Carlos, the project, under the coordination of researcher Luiz Henrique Capparelli Mattoso, also involved important partnerships – the Institute of Physics and the Institute of Mathematical Sciences and Computing of the University of São Paulo (USP), in São Carlos, USP’s Polytechnic School, Embrapa Grapes and Wine, in Bento Gonçalves (RS), and the Food Technology Institute (Ital), of Campinas. In addition, is was closely accompanied by an illustrious collaborator, the New Zealander naturalized American Alan MacDiarmid, a professor at Pennsylvania University and winner of the Nobel Prize for Chemistry in 2000, along with Japan’s Hideki Shirakawa and Alan Heeger, an American.

In November last year, the electronic tongue was awarded one of the most important prizes in the country in the area of scientific and technological development – the Governor of the State Prize, granted by the State Service for Assisting Inventors (Sedai), of the Secretariat for Science, Technology and Development, in the Brazilian Invention category.

Highly sensitive
The electronic tongue works in a very similar way to the human one. It is capable of recognizing flavors: sweet, salty, sour and bitter. The difference is that is manages to measure concentrations well below the limit for biological detection. For the human palate, it is only possible to recognize a drink as sweet if the concentration of sugar is more than 685 milligrams (mg) for a glass (200 milliliters) of water. But the electronic tongue manages to detect only 342 mg of sugar in the same quantity of water. For salt, the electronic tongue detects only 58 mg of salt in a glass of water, whereas the human tongue needs at least 117 mg.

The secret lies in the six sensors that are used by the device. They are made up of microelectrodes covered with an ultrathin layer of conductive polymers (plastics that conduct electricity), which include in their composition substances that are present in human saliva, like the lipids. When dipped into a drink, the polymer compound interacts with the substances present in the liquid and sets off a specific electric response for each substance, which is captured by the electrode and sent to a computer. The signals received from the electrodes are then interpreted and converted into a graph, a sort of digital signature of the drink.

The electronic tongue is the result of various research projects that made it possible to synthesize conductive polymers to which substances have been added to make them sensitive to specific flavors. Polyanilines, for example, are polymers that interact with acid substances present in drinks and make it possible to detect a sour flavor. Developed by chemist Alan MacDiarmid, this technology was brought to Embrapa by Mattoso as part of his doctorate in the United States, under the direct supervision of the father of the idea. In Embrapa, some 40 polymer compounds have now been studied, specifically to detect various patterns of palate.

The conducting polymer based sensors are also capable of measuring the concentration of minerals present in the water. This allows the electronic tongue to distinguish perfectly between tap water and mineral water, or ultrapure water (deionized and distilled), as well as to detect contamination by heavy metals like lead, chrome and other toxic metals.

Ultrathin films
The challenge now is to develop sensors for detecting contamination by pesticides in rivers and water springs and sources. The foundations for facing this new challenge were laid down in a project that precede the electronic tongue. Under the coordination of researcher Carlos Vaz, also from Embrapa, it made it possible to develop equipment to detect the two herbicides widely used in sugar cane and soybean crops, to fight the growth of broad leafed weeds: Imazaquin (also known as Scepter) and Atrazine, products that can cause cancer. Part of the water used in spraying the herbicides over the plantations runs into the water courses and penetrates the soil, contaminating the water tables. “The next step is to develop an electronic tongue with specific sensors for detecting these substances and to compare results”, Mattoso explains.

Besides the polymer composition, another determinant factor for the great sensitivity of the electronic tongue is the way how the electrodes are covered. “The thinner the layer of polymer, the more easily the drink is absorbed, which makes the electrical response almost immediate”, says the researcher. This is why the electrodes are covered with ultrathin films, or nanofilms, which have the thickness of just one layer of polymer molecules (millionths of a millimeter). Two techniques are used. The self-assembly is done at Embrapa, by post doctorate scholar Antonio Riul Júnior, and deposition, by the Langmuir Blodgett technique, which consists of the deposition of a film, to be covered by gold electrodes, with the collaboration of Professor Osvaldo Oliveira, from USP’s Institute of Physics in São Carlos.

All the components of the device were developed in the project. The microelectrodes are made in gold at the Microelectronics Laboratory of the Electronic Systems Engineering Department of the São Paulo Polytechnic School, also of USP, under the coordination of Professor Fernando J. Fonseca. The software that analyses the electrical signals captured by the sensors is being developed in partnership with Professor André Carvalho, of USP’s Mathematical Sciences and Computing Institute, in São Carlos. The program is based on neural networks, a system that works in a similar way to the human brain and allows being “trained” to analyze different kinds of drink.

Over the last six years, research with the electronic tongue at Embrapa has resulted in the formation of four students for a master’s degree and five for a doctorate, and there are 11 research projects under way at the moment. The scientific text was published in the Langmuir magazine, of the American Chemistry Society, in January, and the subject has now showed a presence even on the site ofNature magazine, also in January.

Differentiated flavors
“There is great interest on the part of the beverage industry”, explains Mattoso. In the wineries, for example, the equipment is capable of telling which is the vintage of wines that are of the same brand. There are many advantages. “The tongue does not get tired, which allows it to monitor production continuously. And it can also test products, like medicines, that could be a health risk to the taster.”

Even with these advantages, he makes a reservation: “The electronic tongue was not designed to replace the work of a specialized taster, to help him”. This is because, despite being capable of distinguishing between wines, it cannot manage to know which of them is going to please the human being. When it is a question of palate, it is the human tongue, for the time being at least, that has the last word.

The project
Use of Alternating Current Electrical Measures to Characterize Polymer Sensors with an Interest for Agroindustry (nº 00/11177-9); Modality Regular research benefit line; Coordinator Luiz Henrique Capparelli Mattoso – Embrapa; Investment R$ 32.470,12 and US$ 31.794,55