Garlic!

Chemistry could reveal the origin of the pungent tastes of garlic and onion, according to researchers at the University of Liverpool. Onion (Allium cepa) and garlic (A. sativum) are well known for their strong flavors, their ability to bring a tear to the eye and a whole host of possible health benefits. However, what is not entirely clear is the origin of the precursors for the various compounds that produce all these effects.


Meriel Jones

According to Liverpool biologists Meriel Jones, Jill Hughes, Angela Tregova, Jonothan Milne, Brian Tomsett, and Hamish Collin, each species has a characteristic set of volatile sulfur compounds that are generated by the enzymic cleavage of odorless chemicals known as S-alk(en)yl cysteine sulfoxide flavor precursors. This group of compounds includes methyl cysteine sulfoxide, methiin, the garlic odor S-allyl cysteine sulfoxide, the oniony S-trans-prop-1-enyl cysteine sulfoxide, and S-propyl cysteine sulfoxide.

As part of a €6.1 million ($7.5 million) EU-funded project, the team has now discovered a putative biosynthetic pathway using molecular biological studies and measurements of sulfur compounds in onion and garlic. This, they say, "may involve (thio)alk(en)ylation of cysteine or a precursor such as O-acetyl serine followed by oxidation to form the flavor precursors." They suggest that variable sulfur availability in the soil may play a role in controlling flavor in different species. They also add that finding the origin of the alk(en)yl groups opens up this field of research to new studies.