August 20, 1997

Acree's Artificial Mouth Takes the Guesswork Out of Tasting

by Linda McCandless

Geneva, NY - Flavor chemists at Cornell University's Agricultural Experiment Station in Geneva, NY, have developed an artificial mouth, called the retronasal aroma headspace simulator, to chew food along with simulated saliva and discover important odors released in the mouth. Deborah Roberts, a graduate student in the Department of Food Science and Technology laboratory of Terry E. Acree, where Charm analysis and, more recently, the aroma simulator were developed, reported on the new simulator to the American Chemical Society at the national meeting in Anaheim, California, in April.

The retronasal aroma headspace simulator is really a glorified Waring blender, operating at body temperature and in tandem with a gas chromatograph. Roberts noted that it will not send human taste-testers to the unemployment line.

"Instruments like the gas chromatograph will detect the volatile peaks for all the compounds in a complex food or drink, but that doesn't mean every compound has an aroma. Our own senses, working in a system like Charm analysis (gas chromatography olfactometry), are the best judges of important flavor compounds," said Roberts.

Flavor chemists have been looking for a better way to measure retronasal aromas, Roberts noted. Retronasal aroma is the smell sensation we get when we eat food and flavor volatiles move through the "back entrance" or nasopharynx to the olfactory organ. In contrast, orthonasal aromas pass through the external nares, the nostrils of the nose, and often produce a different sensation.

Wine tasters, for example, have different experiences from orthonasal and retronasal aromas. The Concord grape note of some American wines or the undesirable "mousy taint" must be in the mouth to be fully appreciated.

"We smell for a wine's bouquet, but some notes can't be picked up by sniffing," reported Roberts.

Some differences between orthonasal and retronasal aromas have to do with chemistry, particularly with the saliva that is blended with foods and beverages in the mouth. Saliva is usually neutral with a pH of about 7, the graduate flavor chemist said. Furthermore, mastication - the act of chewing - changes food, and temperature is important, too. Ice cream, if sniffed in its frozen state, does not reveal all the aromas to hint at its taste sensations. But warmed in the mouth, ice cream is a whole different experience.

The retronasal aroma headspace simulator takes all those factors into account: Artificial saliva is mixed with the food being tested, the blades of the device turn at about 30 revolutions per second to simulate chewing, and a copper-coil water jacket warms the artificial mouth to body temperature. The machine will perform its artificial mastication from 10 seconds to 10 minutes--longer than mother ever insisted we chew our food.

Odor-causing volatile compounds are sampled from the device's headspace, the space above the surface of the food, which is what the olfactory organ senses. The compounds are then run through a gas chromatograph for identification, where the detector is either an instrument or a human sniffer. The human sniffer in the Charm analysis process judges which of the separated compounds are important to the aroma sensation.

The original artificial mouth really was a Waring blender, Roberts recalled, but the chemists turned to a somewhat more sophisticated version, a laboratory mixer made by the Eberbock Corp., because the lid needs to be airtight.

So far the artificial mouth has been testing model systems and raspberries, Roberts told the American Chemical Society symposium on graduate research. The next course on the menu will be high- and low-fat foods, in an attempt to learn what effect oils have on the aroma sensation.

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Contact: Linda McCandless
315-787-2417
e-mail: llm3@cornell.edu
Communications Services, Geneva, NY