04 Nov 2011 The sweet smell of chocolate: sweat, cabbage and beef
Chocolate is one of the most popular foods in the world, but the details of its taste and aroma profiles have long eluded scientists. However, new science is revealing why cocoa’s potent sensual properties have been so difficult to pin down.
A recent analysis found that the individual aroma molecules in roasted cacao beans (the primary ingredient of chocolate) can smell of everything from cooked cabbage to human sweat to raw beef fat.
Together, more than 600 of these flavour compounds melt together in just the right combination to yield the taste and scent of what we all call chocolate, according to Peter Schieberle, a food chemist at Munich Technical University and director of the German Research Center for Food Chemistry, who presented the data at this year’s meeting of the American Chemical Society in Denver.
Most of the molecules that comprise a food’s aroma are volatile, which means they transform into gases easily at room temperature. These volatile compounds are inhaled along with the air we breathe, bringing them into contact with the 900-plus odorant receptors in the upper half of the nostril.
In the early 1990s scientists Linda Buck and Richard Axel began the work that would show each odorant receptor recognised one particular compound and was linked to a specific olfactory neuron in the nostril. As a volatile aroma compound latches onto an odorant receptor, it triggers the firing of the olfactory neuron (Buck and Axel won the 2004 Nobel Prize in Physiology or Medicine for their discovery). Complex aromas form when multiple volatile compounds trigger their respective olfactory neurons at the same time. The brain identifies flavour by measuring how frequently the different neurons fire.
“By the time you put four chemicals together, your brain can no longer separate them into components. It forms a new, unified perception that you can’t recognise as any of those individual aromas,” says Gary Reineccius, a food scientist at the University of Minnesota.
Processed foods such as chocolate, beer and tea contain thousands of aroma compounds. This multiplicity of molecules creates a mosaic of odor in the brain as each individual molecule contributes a hint of scent to the final flavour.
Just as our brains can often assemble a whole picture from seeing just a sketch of an image, Schieberle and colleagues found that humans can recognise chocolate aroma using only 25 of its 600-plus volatile compounds. Of these, many are also found in much less appetising items, including cooked cabbage, raw beef fat and human sweat, which are in turn also composed of many different volatile compounds.
Even so, not one of these 25 key compounds can be pegged as a “chocolate” aroma…..
Scientific American: Read the full article here