Despite garlic's popularity, the compounds responsible for its pungency, as well as the receptors through which we perceive those compounds, have largely remained a mystery.
But scientists report this month that raw, not baked, garlic elicited responses from two so-called TRP ("trip") channels, TRPV1 and TRPA1, which belong to a family of receptors that can be activated by temperature and chemicals.
These findings, combined with past studies, indicate that thermosensitive TRP channels play a key role in the phenomenon of chemesthesis (the somatosensory contribution to the sense of taste), which is experienced, for example, in the heat of chilli peppers or the coolness of peppermint.
TRPV1 is known to respond to noxious (painful) heat and to the pungent component of chilli peppers, whereas TRPA1 is activated by noxious cold and by pungent compounds found in cinnamon oil, mustard oil, and wintergreen oil.
Both TRPV1 and TRPA1 are found in pain-sensing neurons that stimulate the mouth and tongue.
The researchers went on to identify the sulfide compound allicin, an unstable chemical found in bruised, cut, or crushed garlic, as the chemical responsible for the activation of TRPV1 and TRPA1 and as the likely key chemical component responsible for garlic's pungency.
Allicin is converted to a variety of more stable sulfide compounds over time or with heating, in correspondence with the significantly milder taste of roasted garlic.
Indeed this active compound is enjoying a certain growth, mostly in garlic supplements, on the back of recent science that suggests it may lower blood cholesterol, blood pressure and blood sugar.
Garlic supplements are worth more than $100 million in the US and are also one of the biggest sellers in the UK market. And a garlic extract (supplied by UK firm Allimax) was recently added into the formulation of new product from US functional drinks company V-Net Beverage, thought to be the first time a garlic extract has been added to a functional food.
On the commodity side for garlic, otherwise known as Allium sativum L. and a member of a very large genus (over 500 species) of cultivated plants which includes onions, leeks, shallots and chives, statistics from the Food and Agriculture Organisation (FAO) reveal in 2003 the EU15 imported some €37.4 million worth of garlic on 47,947 Mt.
Full findings of the study carried out by a team led by Ardem Patapoutian of The Scripps Research Institute and the Genomics Institute of the Novartis Research Foundation are published in the 24 May issue of Current Biology.