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Chemical Communication


Biochemistry to boost garlic breath and canine COVID-19 detection

by Laura Howes
October 3, 2020 | A version of this story appeared in Volume 98, Issue 38


Good news for garlic lovers

A garlic bulb with the structure of allicin superimposed.
Credit: C&EN/Shutterstock
Something stinky: Understanding how allicin is made could lead to stinkier and subtler-smelling garlic bulbs.

Booster of flavor, repeller of vampires, stinker of breath. Garlic has enhanced our cooking for thousands of years by adding different flavorful sulfur-containing compounds to our dishes. The punchy allium has also been a folk remedy for infections, including plagues and other medical complaints, for almost as long. But even with all we know about it, the humble garlic clove is still giving up some sulfurous secrets.

At Virginia Tech, graduate student Hannah Valentino has picked apart a previously unknown pathway to one of the key flavor compounds in garlic, allicin (J. Biol. Chem. 2020, DOI: 10.1074/jbc.RA120.014484). Allicin is the flavorful compound with a characteristic smell that’s released when you cut or crush raw garlic. Somewhat unstable, allicin will break down over time, or with cooking, to create the other smelly compounds that many people find alluring in food but less so on the breath.

Trying to understand the biosynthesis of this stinky compound, Valentino found an enzyme that oxygenates allyl mercaptan to form allyl sulfenic acid. Two molecules of the allyl sulfenic acid then condense to form allicin.

In a press release about the paper, Valentino’s mentor Pablo Sobrado suggests that understanding how the enzyme creates garlicky flavor compounds could help researchers develop new garlic breeds with different allicin levels. That could help farmers grow garlic they know will have a receptive audience: consumers in the future could buy garlic bulbs with levels of the flavorful compound that suit their tastes.

For now, though, if you are more worried about stinky breath than keeping vampires away, Harold McGee’s On Food and Cooking: The Science and Lore of the Kitchen may help. “Residual thiols in the mouth,” McGee writes, “can be transformed into odorless molecules by the browning enzymes in many raw fruits and vegetables.” His advice­—eating a salad or apple should remove garlic’s offensive odors from your exhalations.


K-9 versus COVID-19

A dog at Helsinki airport sniffing different samples.
Credit: Finavia
Good doggo: The superior noses of our canine friends are helping screen passengers at airports for COVID-19.

While we know a lot about the smell of garlic, researchers still haven’t pinned down the source of the novel coronavirus’s scent. But airports are now using scent-trained canines for dog-based diagnostics.

In July, Newscripts reported that researchers were having success training doggy detectives to sniff out people infected with COVID-19. But those tests were in the lab and based mostly on smelling urine or saliva from infected people. Not ideal for day-to-day testing in a public setting.

The article prompted a representative from the United Arab Emirates Ministry of Interior to contact Newscripts via email. Since August, the note says, scent-detecting dogs have been sniffing out COVID-19 at airports, including in the busy hub of Dubai. Instead of taking saliva samples, which might be infectious, medical assistants at the UAE airports take sweat samples for dogs to sniff, which the representative says “are completely safe for both the dogs and the medical assistants who are administering the test.” In late September, COVID-19-detecting doggos started working at Helsinki’s airport, where they are also sniffing swipes from passengers’ skin rather than the passengers themselves.

It still isn’t clear exactly what combination of metabolites and scent molecules gives people infected with SARS-CoV-2 their distinctive scent. But Newscripts hopes that researchers can find that elusive eau de COVID-19. Until that is figured out, we’re glad these pooch sleuths are helping out and we hope these good puppers get lots of treats at the end of a tough day at the office. That always works for the Newscripts gang.

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