Is that Folgers coffee in your cup or Maxwell House? Now you no longer have to rely on your nose to tell. Researchers have developed an analyzer that can distinguish between 10 commercial brands of coffee and can even tell apart coffee beans roasted at various temperatures for different times. The advance could help growers determine within minutes whether a particular batch of coffee is just as good as the previous one or whether it's undrinkable.
Researchers have been trying for years to come up with a simple way to analyze coffee. But it's no easy task. The challenge is that the aroma of roasted coffee beans consists of more than 1000 compounds that change with roasting temperatures and time. Traditional methods of chemical analysis like gas chromatography combined with mass spectrometry generally have difficulty distinguishing between compounds that are very similar to one another. And "electronic noses," an array of dyes, and other sensors that change color or chemical properties when they react with certain molecules suffer from the same drawback.
Over the past decade, chemist Kenneth Suslick and colleagues at the University of Illinois
, Urbana-Champaign, have refined the electronic nose approach. In the new study, they used dyes that interact strongly with other chemicals, making them more specific. They then put drops of 36 dyes on a polymer film the size of a nickel. The pigments in the dyes belonged to a range of chemical classes, including metalloporphyrins (a class of molecules which give blood and chlorophyll their distinctive colors); pH indicators; and molecules that change color with certain chemical vapors.
The device produced a pattern of colors as each coffee's mixture of volatile compounds interacted with the dyes. When the investigators pumped vapors from various coffees including Starbucks Sumatra Roast and Folgers Grande Supreme Decaf-over the arrays, all generated unique color patterns, like a molecular "fingerprint," they report this month in Analytical Chemistry.
The array doesn't give any information about the individual compounds in the aromas. "The important thing is that we can easily tell the difference between different roastings and coffees," notes Suslick. And that should help growers quickly and cheaply analyze problems with coffee, such as burnt flavors, during their initial screening process says food scientist Felix Escher at the Swiss Federal Institute of Technology Zurich.
The applications for the kind of device created by Suslick's team go beyond coffee, says chemist Pavel Anzenbacher Jr. at Bowling Green State
University in Ohio
. Similar arrays, he notes, could be used in everything from detecting explosives to spotting contaminants in toothpaste | 
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发表于 2012-4-4 08:36:42
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