Many people know her from a vacation in Southeast Asia: the durian fruit is famous for its heavenly taste – but also for its hellish smell. German researchers have now uncovered which substance is responsible for the development of the typical durian smell. Surprisingly, it is a rare amino acid that is considered to be potentially harmful to health. But stinkfruit lovers don’t have to worry, the scientists say.
“Durian fruits must not be brought onto the hotel grounds!” Many tourists are familiar with this rule from their Thailand vacation and in Singapore it is even forbidden to take the fruit on public transport. The reason: there is a threat of public annoyance because the durian spreads a smell that is reminiscent of putrid onions. Once set, it should hardly be possible to drive it out of rooms. Nevertheless, the durian is a popular delicacy in many Southeast Asian countries. Anyone who bites into the creamy pulp despite the smell can enjoy a real aroma explosion, it is said. In addition, the fruit of the civet tree contains many nutrients and is even said to have healing powers.
On the trail of the stench
For some time now, a working group from the Leibniz Institute for Food Systems Biology in Munich has been investigating what is the basis of the infamous smell of durian fruit. They have already been able to show which substances get into our noses: The Durian therefore exudes the sulfur-containing odor substance ethanethiol and compounds derived from it. In their current study, the researchers were now able to uncover the biochemical way in which the plant produces these volatile substances. The precursor compound of the malodorous substances is therefore the rare amino acid ethionine.
“Our studies suggest that when the fruit ripens, a plant-specific enzyme releases the odorant from the ethionine,” reports lead author Nadine Fischer. “This also fits our finding that not only does the concentration of ethionine in the pulp increase with increasing ripeness, but also that of ethanethiol. The latter explains the particularly strong smell of ripe durian fruits, ”says the food chemist.
Disreputable in two ways?
The finding is particularly explosive against the background that ethanethiol is known as a potential hazardous substance. Animal and cell culture studies show that the amino acid in comparatively high concentrations can cause liver damage and cancer. “So the question arises whether eating the fruit can be associated with health risks,” says study leader Martin Steinhaus. As he emphasizes, there is also evidence that low concentrations of ethionin could have positive immunomodulatory properties. “Knowing exactly how much ethionine is in the durian fruit is therefore not only interesting because of its importance for the smell,” says Steinhaus.
According to the researchers, further studies should now clarify which health aspects could be associated with the consumption of durian fruits. However, Steinhaus does not see a great danger potential: “In order to ingest a dose of ethionine that had negative effects in animal experiments, a person weighing 70 kilograms would have to eat 580 kilograms of pulp of the particularly ethionine-rich durian Krathum variety in one day,” says the food chemist.
Source: Leibniz Institute for Food Systems Biology, professional article: J Agric Food Chem, doi: 10.1021 / acs.jafc.9b07065