Why strawberries taste like strawberries
Researchers have discovered what gives ripe strawberries their characteristic aroma. According to the team at Technische Universität München (TUM) in Munich, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) plays a fundamental role in producing the strawberry’s distinctive flavour. Professor Wilfried Schwab, Head of Biotechnology of Natural Products at TUM has spent many years researching HDMF’s structure. “A ripe strawberry has a particularly high concentration of this compound – up to 50 milligrams per kilo – which lies far above the odour threshold. This compound gives the ripe fruit its characteristic caramel-like aroma.” HDMF is also found in fruits such as pineapples and tomatoes. The aroma develops in these plants in a multi-step pathway that starts with the fruit sugar fructose. In this process, a molecular precursor binds to an enzyme called Fragaria x ananassa enone oxidoreductase(FaEO) which converts it into HDMF. “We were particularly interested in the biocatalytic process that leads up to the final compound,” said Professor Arne Skerra, a co-author of the paper published in the Journal of Biological Chemistry. The researchers mapped this reaction in detail using X-ray structural analysis which allowed them to view the three dimensional structure of molecules. They investigated six different enzyme-molecule combinations in their studies. The team’s findings revealed a previously unknown mechanism for the catalytic reaction. They discovered that the precursor compound is reduced and electrons are specifically transferred to a new particular part of the molecule. Therefore, FaEO represents the first member of a new class of biocatalysts – a discovery which could have implications in industrial biotechnology. “Unlike coffee or vanilla, the biochemical processes that produce the strawberry aroma are very complex. But now our TUM research team has shed light on an important step in its biosynthesis,” added Skerra. Reference: Structural basis for the enzymatic formation of the key strawberry flavor compound 4-hydroxy-2,5-dimethyl-3(2H)-furanone
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