Chemosensory Analysis at Cornell
Chemosensory perception of food
is a conscious experience initiated by chemicals: odorants, tastants, and
chemesthetic substances. Terry Acree and the other scientists in his laboratory
study food composition and its relationship to the chemosensory perception
of flavor. Surprisingly, their studies of odorants in flavor reveal fewer
than 1,000 chemicals at concentrations potent enough to affect flavor in
food. First published by Terry Acree and Henry Arn in 1997, the web data
base called Flavornet lists most of these odorants and cites the research
that first described their potency. Therefore, the diversity of smell experienced
by humans is mediated by a smaller set of chemicals than the hundreds of
thousands commonly estimated.
Using Gas Chromatography – Olfactometry (GC-O) we have explained at least in terms of their most prominent features the odor of complex foods like the Lychee fruit smell in Gewertzraminner wine. It is caused by the presence of a single odorant cis-roseoxide. The presence of a single odorant at “high concentration” sometimes defines the character of a flavor and it usually is the cause of taints, off-odors, and defects that sometimes damage the acceptability of foods. Identifying these compounds is easy most food aroma is not caused by single odorants but are instead an interaction between the odor of several odorants or several odors caused by many odorants. Unfortunately, compositional knowledge produced by chemical studies is not a reliable predictor of the qualitative experience or quale (qualia pl.) produced by most foods or mixtures of their odorants.
In mixtures, odorants affect sensory perception in three fundamental ways. The most common is suppression, or the simultaneous reduction in potency caused by different odorants mixed together. This is different from adaptation, or the reduction in potency caused by a sequential stimulation with odorants. Mixtures will exhibit adaptation over time as the potency of the strongest component is reduced and weaker odors are revealed. Finally, there are odorants that are chemically different but functionally the same. These compounds are additive. To predict flavor perception from chemical composition it is essential to understand how suppression, adaptation and additivity mediate perception. Our lab is developing new method like gas chromatography – pedestal olfactometry (GC-PO) and two dimensional gas chromatography – olfactometry (GCxGC – O) to study odorants in mixtures in much more detail and at much lower concentrations.