Researchers have found the key compound responsible for the distinctive caramel-like aroma of the humble strawberry.
Strawberry's aroma is actually the product of around a dozen different compounds, with Furaneol being particularly important to the smell of the ripe berry, a new study has found.
Scientists from the Technische Universitat Munchen (TUM) in Munich decided to find out what gives strawberries their characteristic flavour.
They found the characteristic aroma of a fresh strawberry is the result of around a dozen different aroma compounds. One of these plays a particularly important role: HDMF, also known as Furaneol.
"A ripe strawberry has a particularly high concentration of this compound - up to 50 milligrammes per kilo - which lies a far above the odour threshold. This compound gives the ripe fruit its characteristic caramel-like aroma," Professor Wilfried Schwab, head of Biotechnology of Natural Products at TUM, said.
HDMF is also found in pineapples and tomatoes. In plants, the aroma develops in a multi-step pathway from the fruit sugar fructose.
"We were particularly interested in the bio-catalytic process that leads up to the final compound," said Prof Arne Skerra from the TUM Chair of Biological Chemistry.
In this process, a molecule precursor binds to the FaEO enzyme, which converts it into the final product, namely HDMF.
Scientists were able to map this reaction path in detail. To understand how enzymes catalyse the bio-synthesis of these new metabolic products, the research team took advantage of X-ray structural analysis.
This allowed them to view the 3D structure of the molecules.
"For the strawberry aroma, we investigated altogether six different enzyme-molecule combinations - and ended up understanding how FaEO produces the HDMF flavor compound," said Dr Andre Schiefner from the Chair of Biological Chemistry.
Scientists discovered that the catalytic reaction involved a hitherto unknown mechanism. The compound is reduced and electrons are specifically transferred to a particular part of the molecule.
The FaEO enzyme represents the first member of new class of bio-catalysts - a discovery which could lead to useful applications in industrial biotechnology.
