Have you ever shared a whiff of black Périgord or Italian Alba winter truffles with a friend, only to have had two totally different reactions? Those of us with a sworn love for truffles are often perplexed by the very notion that anyone could harbor a dislike for the prized fungi. Well, turns out it has everything to do with the genetic variations of our human odor receptors, and how they affect our perception of the aroma compounds present in truffles like dimethyl sulfide, 2-methylbutanal and androstenone.
Good scents or good sense
For starters, each of us has a unique set of olfactory receptors. About 140 of our 400 odor receptors vary slightly from one person to the next, causing us to perceive the scents in our environments differently. It’s the reason why a certain fragrance that smells heavenly to you may smell awful to someone else.
So what is it about the odor of a truffle that some of us find so alluring? Each species has its own distinct aroma profile made up of many different volatile compounds, but there are a handful of aroma types and descriptors that are typical for both black and white truffles. Black truffles have a sulfurous oniony and cooked cabbage-like scent, as well as some fruity, roasted notes that give the fungi an almost fruity chocolate-like nuance. The sulfurous vegetable odor of the compound, dimethyl sulfide, is a key volatile found in 85 percent of black truffles and is what draws trained dogs, pigs and other animals to their hidden location beneath ground.
That's not 'truffle' oil!
You’ve probably seen ‘truffle-infused’ products in fancy food stores, but don’t be fooled by the labels. These gourmet scented oils are made using synthetics that usually combine just two compounds—dimethyl sulfide and 2-methylbutanal (think: wet dog)—to imitate the scent of black Périgord truffles because the unique, earthy mix of a hundred or so sulfides, alcohols, esters, ketones and aldehydes that make up their subtle aroma profile is so volatile that the fragrance simply would not last in a bottle.
In a study from 2007, American researchers also looked at how genetic variations in the human odorant receptor OR7D4 affect our perception of androstenone, a type of pheromone that truffles contain in small traces. Androstenone is a chemical derived from the male sex hormone, testosterone. In pigs, the musky scent of a boar’s androstenone is known to arouse female sows. It was previously conjectured that truffle hunting pigs were attracted to the scent of androstenone when foraging for the fancy fungi.
Genetic variations of our human odor receptors affect our perception of the aroma compounds present in truffles.
Humans also produce androstenone in the form of body odor and urine. In their study, the researchers first tested the sweat chemical against the 400 or so odor receptors responsible for our human sense of smell. They then surveyed 400 test subjects after sequencing their DNA to determine if there was, in fact, any correlation between their genetic variations in the odor receptor OR7D4 and the participants’ reactions to androstenone. What they found was that some of us perceive androstenone as “offensive (‘sweaty, urinous’), pleasant (‘sweet, floral’) or odorless.”
What’s so special about truffles? Or not...
If none of this rings a bell, then you’re probably among the 25 percent who can’t detect androstenone and have always wondered what all the fuss over truffle season is about. Only a lucky 35 percent of people are wildly drawn to their scent, while the remaining 40 percent of the population are completely put off by them. Those of us who are hypersensitive to—and actually turned off by—their earthy, musky odor are left to puzzle over why truffle connoisseurs swoon and fork out hundreds or even thousands for the best, most odoriferous Périgords and Albas.
It just goes to show that perception of smell really is in the nose of the beholder!