What is the smell of truffle fungi made of?
Summary: Truffle owe their smell to odorants, small molecules that connect to smell receptors inside the human nose. Odorants are studied by specific food scientists that employ a technique known as olfactometry to identify odorants. Such olfactometry studies have demonstrated that the smell of any truffle sort is due to the combination of 13-20 odorants. White and black truffles odorants were first identified by an Italian and a French scientist in the 60's and 80's. This quickly led to the formulation of synthetic truffle flavors by the food industry. Those flavors are still widely in use today despite their questionable ability to mimic the flavors of authentic truffles.
Tell me more…
The enticing smell of a truffle fungus or actually any food comes from small molecules known as odorants that are trapped inside that food but readily become gaseous and reach our nose. Inside the nose, these odorants bind with specific receptors, triggering nerve impulses that will pass on the information about the odor to our brain.
Identifying the structure and the smell of odorants is done by a specific group of food scientists known as “sensory scientists” that have advanced knowledge of chemistry. They rely on a technique called “Gas-Chromatography-Olfactometry” to characterize odorants. The technique consists in first separating odorants from their initial mixture by Gas-Chromatography. This allows people to smell individual odorants one by one as they exit the instrument (this is the second step, the olfactometry part), and report on odor intensity and characteristics.
Characterizing the smell of many truffles by the latter technique has revealed that it´s the combination of 13-20 odorants that make up the typical smell of any truffle sort. Let's now take a historical perspective on the study of truffle aroma to learn more about truffle odorants.
A historical perspective on the study of truffle aroma
Truffles are naturally found all around the globe and have even been introduced in places where they might not have existed before (i.e. New Zealand). Looking back far in time though, to the end of the Medieval Period, truffles were most famous in France and Italy, where they still abound. It is therefore not surprising that Italian and French scientists were the first to characterize the smells of truffles.
In 1967, the major odorant of white truffle, “truffle sulfide”, also known as 2,4-dithipentane to chemists, was identified through a collaborative work of the Italian chemist A. Fiecchi from the University of Milan and the flavor company San Giorgio Essences based in the nearby city of Turin. It is interesting to note that truffle sulfide, has a smell reminiscent of white truffle, however, taken alone, its flavor is far from the complexity and nuances of actual white truffles. Indeed, other odorants are needed to reach an actual white truffle smell. This was demonstrated in 2017 by two German scientists from the University of Munich, C. Schmidberger and P. Schieberle. They proved that an authentic white truffle flavor was made of the combination of 11 odorants, including of course 2,4-dithiapentane, and 10 more odorants with flavor notes of butter, mushroom, malt, and more.
The flavor components of the black truffle Tuber melanosporum were identified in 1989 by the French chemist T. Talou at the University of Montpellier in Southern France. In a patent filed in 1986, Dr. Talou noted that the combination of two odorants with cabbage and malt-like smells could reproduce quite well black truffle aroma and that additional components would add complexity. Twenty-four years later, the Spanish scientist L. Culleré completed the picture by showing that as many as 17 odorants could be necessary to convincingly reproduce the smell of the black truffle.
Over the last decade, the flavor profile of many more truffle sorts has been described. For instance, my own work in collaboration with an American colleague on the whitish truffle known as the “bianchetta” has shown that it contained unusual odorants with characteristic smell of grilled onion, bacon, and rubber. We went further in that work and as for the two examples described above, could show that the overall smell of that truffle could be due to the combination of up to 13 odorants.
Key odorants of different truffle sorts, including the three truffles described above (white, black, and whitish) differ in chemical structure (that is the number of carbon atoms or the way these carbon atoms are connected among each other or to other atoms). One thing they have in common though is the presence of a sulfur atom within their carbon atom backbone. The human nose is very sensitive to odorants containing sulfur atoms. Considering that numerous sulfurs containing odorants differ in structure among truffle species, this partially explains differences in smell among truffle sorts.
So how were these discoveries taken up by the food industry?
The discovery of the major odorant of white truffle was quickly taken up by the food industry since “truffle sulfide” could easily be obtained by chemical synthesis. This created a kind of “gold rush” already in the 80's since food products having the smell of white truffles could be sold at a very high premium. These flavors, still widely in use today, have extensively been criticized but we will tell you more about this in a subsequent blog.
The food industry currently claims to offer food products with three truffle sorts (white, black, and summer truffle). At least this is what one commonly sees on labels and packaging. Inconsistencies however abound, since the majority of products that are supposed to contain black or summer truffles actually smell like white truffles. This is so because flavors containing synthetic white truffle odorants are used irrespectively of the truffle sort shown on the packaging. This is an offense to the nose of most foodies who have tried actual truffles. It is even more surprising since a patent was filed by T. Talou when he characterized the odorants of the black truffle (1988). It seems that over time Italian flavor companies won the battle even against French ones and prevailed to the extent that one-flavor-fits-all dominates the market and people now believe that all truffle smell of white truffles.
But I like to believe that there is a glimpse of hope, and getting this straight is our battle now and the reason why the startup Nectariss came to life. We are bringing to market truffle flavors that are made from real truffles and that have authentic flavors (no “one-flavor-fit-it-all”). More about our approach to fermentation to produce truffle smell in an upcoming blog.
Why is this relevant?
Identifying the flavor components/odorants responsible for the smell of truffle fungi is relevant since it can help in determining product authenticity (is an oil made of real truffle or from aroma chemicals?). Understanding that real truffle sorts smell drastically different because their key odorants differ in structure also highlights that the current solution proposed by the food industry “one-flavor-fits-all” is far from authentic. It is a bit as if every wine would smell the same, regardless of the grape variety or the harvest region. Foodies please beware and spread the word!
Written by Richard Splivallo
Richard is the CEO of Nectariss and a truffle expert. As a former university professor, he has dedicated almost 20 years of his life to better understand the complex biology of truffle fungi and has authored more than 25 scientific publications on that topic.