Researchers sniff out aroma’s role in taste

Brian Close

One day, low-fat foods could be as tasty as their higher-fat counterparts, thanks to researchers in the Department of Food Science and Nutrition.
Gerhard Zehentbauer, a post-doctoral associate in the department, is a German citizen from Munich. He received his Ph.D. in food chemistry from the Technical University in Munich with a thesis on the aroma of French bread crust.
Traveling to Australia, Zehentbauer studied red wine for a year at a wine research institute. He came to the University last spring and is working for two years on the flavors in cheddar cheese.
“The key idea is that high- or regular-fat cheddar cheese smells and tastes better than low-fat cheese,” he said. “The key question is, ‘Why?'”
Other researchers in the department are working on a variety of problems in the field, said Geri Skogen, assistant to the department head.
“There is research in cereal grains, the physical chemistry of foods, genetic engineering, food safety and factors affecting food acceptability,” she said.
To find out what causes a bad taste, food science researchers attempt to locate the aroma compounds — chemical compounds that have an odor.
Devin Peterson, a doctoral candidate working on the aroma compounds of heated butter, said low-fat foods don’t closely match the original.
“In low-fat foods, the flavors are usually off because the concentrations of the aroma compounds in the air above the food have been altered,” he said.
The aromas of a food are important because the perception of taste comes from both the tongue and nose, Peterson said.
The tongue, he said, perceives salty, sweet, sour, bitter and perhaps a brothy or savory fifth taste called umami. The rest of the nuances of taste are filled in by the nose.
“You will taste the salt in the butter on your tongue, but the butter flavor perception will come from the aroma compounds which are perceived in the nose,” he said.
After removing those compounds from the food using a solvent or through evaporation, Zehentbauer injects the solution into a machine called a gas chromatograph, which separates the compounds and creates a chart with peaks representing the compounds, some of which have an odor.
The researcher puts his nose over a tube and notes the smell, if any, of each particular compound as it is being drawn.
After identifying the compounds that have odors, Zehentbauer must find which are the most important by diluting the mixture and retesting for smells.
“The key idea is that compounds that we can perceive all the way down are the more important ones,” he said.
Zehentbauer said the nose is very good at determining if an odor is present or not but has problems determining the intensity of the odor. After diluting the compounds, the researcher needs only to detect the presence of the smell.
Once Zehentbauer has a picture of all the important compounds, he can mix a new solution with the aroma compounds and compare it with the original solution using test subjects in what is known as “sensory testing.”
The world of smells requires a special vocabulary. Testers must be able to consistently describe a smell using words like “malty” and “roasted.”
Even when the researchers have a good picture of the aroma compounds, their job is not done. Often they will try to find ways of producing a food with the tastier mixture, requiring them to analyze how the compounds are formed when the food is produced.
“If you have a better understanding of what is really required for a good butter flavor, you could accentuate desirable flavor attributes,” Peterson said.
Zehentbauer said his knowledge of smells causes some foods to be noticeably overbearing.
“Yogurts and candies are often over-flavored,” he said. “There’s way too much inside that has nothing to do with strawberry or cranberry.”
He said foods in the United States have been over-flavored for years, training people to desire that added flavor. He said he prefers foods with aromas and tastes closer to the natural aromas and consumers could also be trained to do so.
Zehentbauer said he enjoys the United States and will eventually decide whether to stay. He said, however, that he will go where his work takes him, much as he has in the past.
“You can sell nearly anything if it smells or tastes good,” he said.