food aroma molecules
June 27, 2014

Decoding The Unique Characteristics Of Aroma

Alan McStravick for - Your Universe Online

The sense of smell in humans has undergone many permutations as we have traveled through evolutionary time. It was once believed that each successive version of our olfactory ability was weaker than the last. Scientists claimed as our sense of sight became ever greater and required more of our energy, our sense of smell suffered. They cited the gradual reduction of our noses paired with the movement of our eyes closer to the middle of our heads as proof of this phenomenon.

Of course, as Gordon M. Shepherd published in his study in 2004, humans and other primates have actually been shown to possess better senses of smell than previously believed. “If human smell perception is better than we thought,” he explained, “it may have played a more important role in human evolution than is usually acknowledged.”

In her article for redOrbit, April Flowers noted that one of the main tasks of the sense of smell is to detect signs of decay, allowing us and other animals to avoid food poisoning. And while that is an important role for our noses to play, a far more pleasant job for our nose is its ability to discern among the many different aromas of the foods we love and enjoy.

Reading this, when I suggest the aromas of a freshly baked warm loaf of bread or steamed broccoli or strawberries resting on a dollop of whipped cream, it is likely you can experience a recall of the scents of those items without actually smelling them. But just what is it about those foods that give them their distinctive scent profiles? The answer is likely to surprise you.

It is a well-known fact that our sense of taste is aided by our sense of smell. Without a properly working nose, we would be unable to detect the flavors of sweet, bitter, salty, sour and savory. This is because the more than 10,000 identified food compounds contribute to our overall sensory impression of the foods we eat and beverages we drink. Scientists from the Technische Universität München (TUM) and the German Research Center for Food Chemistry (DFA) performed a meta-analysis on the odorant patterns of 227 different food samples to try and understand why and how a certain food smells the way it does.

From frying bacon to the pungent but sweetly sour orange rind to a robust and spicy red wine, the amount of almost infinite aromas available to humans are actually derived from just 230 odorants. Each individual food or beverage item typically only seizes on a combination of between 3 and 40 of these odorants – in specific concentrations.

“So for example, the smell of cultured butter is encoded by a combination of just 3 key molecules, but fresh strawberries have 12,” explained professor Peter Schieberle, chair of Food Chemistry at TUM. Coming in as the most complex of the foodstuffs tested by the researchers was Cognac. The aroma of this popular brandy is comprised of 36 different molecules.

Where this really gets interesting is when the aromatic molecular combination slips past our nostrils, causing our brain to translate them into olfactory stimulus patterns. For this to be achieved, the aroma has to interact with one or more of the 400 olfactory receptors in our nose. “A combination of between just a few key odorants creates an authentic perception of odors,” stated professor Thomas Hoffman, TUM Chair of Food Chemistry and Molecular Sensory Science. He continued, “This is all the more surprising given that the olfactory quality of the combinations is not determined by the individual components."

As the team explains further, a smell is not a smell until the above process has occurred. Were a chemical odor pattern to somehow bypass the olfactory receptors to be processed in the brain, the individual odor components simply wouldn't add up. The individual olfactory notes are necessary for translating that chemical odor pattern into a new odor identity. “In view of the chemical odor code combination possibilities and the 400 or so different olfactory receptors, it appears that there is more or less unlimited number of discernible odor qualities,” Schieberle stated.

“By mapping the odorous substances of the 230 currently known key odors, scientists can test which receptor combinations are 'reserved' for food odors,” explained Hoffman. To date, scientists have identified 42 receptors that respond to food odors – with the majority binding multiple odor molecules. “This will help us explain the biological relevance of odors in even greater detail.”

Moving forward with their work, the team sees great opportunity in biotechnology applications thanks to their work helping to map out odor codes. As an example, working with a better understanding of odor codes of both crop plants and fruits at the molecular level can be useful to breeders. Additionally, the team sees that their findings could serve as the scientific groundwork for the next generation of aroma products.

But perhaps most interesting of all is that this latest odorant mapping will yield a far more precise natural simulation of odors. Imagine a not-too-distant future where text messages will be accompanied by scent messages. Because that future is coming and it smells great.

Findings of this research are published in the journal Angewandte Chemie International.