By Martin Loignon, Ph.D. Molecular Biologist.

Whether a truffle is black or white, its exceptional flavour and rarity along with the ancestral manner in which it is harvested, which requires the presence of a canine or porcine “tracker”, all contribute to its reputation as a quasi-mythical fungus. As the truffle is buried underground, only the great sense of smell dogs and pigs are gifted with is sensitive enough to detect its fragrance, sole indicator of its presence. It is given the French name “truffe”, meaning the nose or snout of these sweet harvest companions.

The rarity of the Périgord black truffle is partly due to the fact that it requires specific soil and climatic conditions as it lives in symbiosis with the oak trees of south-west France, colonizing their roots and exchanging nutriments. Its reproduction system is also very complex; making it nearly impossible to cultivate.

It is also known that the black truffle cohabits with an indigenous microbial flora composed of various microorganisms. Moreover, it has long been believed that these microorganisms were at least partially responsible for the exceptional aromas of the truffle, as are those of raw milk cheeses and wines. We now know that the truffle draws within itself, in its geneticbackground, the ability to produce the aromas so highly prized by epicureans.

A European team headed by Dr Francis Martin from the Institut National Français de Recherche en Agriculture recently published the genome sequence and annotated the 125 megabases* of the Périgord black truffle’s DNA, also known under its Latin name Tuber melanosporum. The study published in the prestigious scientific journal Nature reports that the genome of the Tuber melanosporum is the most complex fungal genome that has been sequenced thus far, and the analysis of these sequences has allowed the identification of 7,496 coded genes for as many proteins.

Proteins accomplish numerous vital functions for organisms by playing roles that are essential in the structure, metabolism, defence and reproduction mechanisms. Certain proteins specialize in the transformation of other proteins and various molecules, designated as substrates, such as amino acids, glucids and lipids. The proteins specialized in the modification of substrates are called enzymes and they act as catalysts, accelerating biochemical reactions. The transformations catalyzed by enzymes can take many forms, and may be either subtle or radical.

Synthesis and degradation represent radical forms of enzymatic transformation as they change the properties of the substrates. This type of reaction frequently occurs during the production of aromatic molecules. For example, the degradation of odourless colour pigments can lead to the production of highly aromatic molecules. It is the case with safranal, which is present in saffron, paprika, black tea and grapefruit, or even the beta-ionone present in raspberries, carrots, apricots and mango. Both are born from the degradation of carotenoids, organic pigments ranging from yellow to orange to deep red, which are naturally present in a variety of foods.

The study by Dr Martin’s team has prompted the discovery of the black truffle’s numerous enzymes that are implicated in the production of aromatic molecules containing sulphur. The sulphur-containing molecules produced include methanethiol, 3-metoxy propanol, dimethyl sulphide, dimethyl bisulfide and dimethyl trisulfide. These molecules are largely responsible for the aromatic signature of the truffle. Granted, each of these molecules emits a sulphurous odour, they also remind us of the smell of garlic, onion and meat, in addition to exuding vegetal notes. Collectively, the mixture of aromas produced by the black truffle also reminds us of musk and of soil, which has led some admirers to qualify as “sexy”.

In addition to revealing the secrets of how the aromas essential to the fragrance of the Périgord black truffle are produced, its genetic characterization has allowed us to learn a lot more on the symbiotic relation it maintains with the oak tree and on its mechanisms of reproduction. This major advancement in our knowledge on the Périgord black truffle will enable us to better understand the obstacles in its culture and also define the precise genetic fingerprint of this species, distinguishing it from the Chinese black truffle, which is frequently sold under false pretence.

To learn more about this research, you are welcome to read the article in its entirety.

*A megabase is the equivalent of 1,000,000 bases, which are the letters of the genetic code alphabet. Copyrights 2011 All rights reserved. For any commercial use, please contact: This e-mail address is being protected from spambots. You need JavaScript enabled to view it