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By Mark Anthony, Ph.D., Technical Editor | 11/19/2007
In the 2005 review "Odor/taste integration and the perception of flavor," in Experimental Brain Research, Dana Small and John Prescott presented psychophysical, neuro-imaging and neurophysiological studies showing how odor and taste are "functionally united [while] anatomically separated." It’s no wonder food manufacturers are very picky about how their products smell.
"Formulating any type of food or beverage involves more than just one’s sense of taste," says Stephen Manheimer, marketing director for Mastertaste (www.mastertaste.com), Teterboro, N.J. "You have to consider aroma, texture (mouthfeel) and, in many cases, even appearance. All of these factors contribute to the overall sensory experience that the consumer has when he sits down to eat. Aroma in particular is strongly linked to taste.
"The taste buds can only perceive five stimuli: salt, sweet, sour, bitter and umami that is, ‘savory’ or ‘meaty’," Manheimer continues. "Because of this, a lot of what consumers experience when eating actually occurs through their sense of smell, not taste. The natural question that comes to mind is, how do we perceive odors or aromas?"
In 2004, neuroscientists Richard Axel of Columbia University, New York, and Linda Buck of Fred Hutchinson Cancer Research Center, Seattle, shared the Nobel Prize for Physiology or Medicine for their contribution to our understanding of how we detect odors. Before they published their work, olfactory scientists knew the cells lining the nose bound a variety of molecules responsible for aroma.
These cells relay electrical signals to a specialized area of the brain called the olfactory bulb, which in turn shuttles messages to the brain’s smell recognition center. However, which receptors on the cell’s surface are doing the work and how exactly these signals are relayed had remained a mystery.
Axel and Buck showed the detection of aromas is highly specific: Each aroma molecule activates a specific receptor on a particular membrane cell of the nasal mucosa. When an aroma molecule binds to a receptor, it sets off a sequence of events involving special signal proteins, called G proteins, which control the opening or closing of channels in the cell membrane.
The surprising discovery was that each cell lining the nasal cavity displays only one type of receptor on its surface, which in turn can be activated by only a handful of related aroma molecules. Since most odors consist of many molecules that activate different receptor-bearing cells with different intensities, we can recognize about 10,000 different aromas.
Axel and Buck further showed the receptor-bearing cells send projections directly to the olfactory bulb. This helps to explain why we are so immediately sensitive to odors, and why separating taste from odor in food is next to impossible.
Most odor molecules are volatized organic compounds. Odor compounds form naturally during the ripening of plants, the development of oils or during natural processes such as fermentation. The list of known natural odorant chemical bases is extensive, ranging from alcohols, aldehydes, amines, esters, ethers and essential oils - anything that can evaporate and reach concentrations high enough for detection. Once identified, the chemicals responsible for aroma can be captured and utilized to enhance the food experience.
The intricate association between aroma and flavor demands rigorous sensory analysis in order to determine what products will be acceptable to the consumer. "Sensory analysis is a critical step in innovation to give consumers the products they want, where, when and how they want them," says Jeffrey Kondo, vice president of product innovation for Dairy Management Inc./DMI (www.dairyinfo.com), Rosemont, Ill.
DMI supports a pilot sensory lab at North Carolina State University’s Southeast Dairy Foods Research Center, Raleigh, N.C. It is part of DMI’s National Dairy Foods Research Center Program, a unified coordinated research effort designed to support and accelerate dairy innovation.
"Very important to industry are the sensory lexicons developed by MaryAnne Drake and her team," says Kondo. Drake is associate professor of sensory and flavor chemistry in the university’s Department of Food Science. "These lexicons not only provide a standardized way of describing flavors but also link these flavors to chemical compounds. When you describe something as having a ‘dairy flavor,’ she’s able to link that to at least some of the compounds that are actually causing that flavor. The descriptions and classifications can help a dairy processor keep going down the right road on a new product," explains Kondo.
Drake’s approach to sensory analysis begins with her knowledge of the physiological ability to detect and distinguish aromas and flavors. "There are many modern instruments designed for sensory analysis, but nothing matches the human instrument for its complexity, intensity and sophistication of detection," says Drake. "Sensory testing is critical. Knowledge of consumer desires and perceptions and the sensory properties of existing competitor products can influence the breadth, depth and success of a product line. The dairy industry is in a desirable position in that its flavor and odor profiles are already pleasing to most consumers."
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