The Chemistry of Raspberries

Raspberries, like all fruits, contain a complex mix of organic compounds. Unlike many fruits, however, raspberries have the less common distinction of lending their name to the compound that is a major contributor to their aroma – and one of the compounds that contributes to their flavour has also been detected in the centre of our galaxy. So, does the centre of the galaxy taste faintly of raspberries?

Before we examine that, let’s start by looking at the aroma of raspberries. A number of families of chemical compounds contribute toward the smell of raspberries, primarily terpenoids, aldehydes & ketones. However, it’s a compound known as ‘raspberry ketone’ (which has the chemical name 4-(4-hydroxyphenyl)butan-2-one)) that is considered the ‘impact molecule’ for the aroma. Its pleasant aroma has seen it used in perfumery, cosmetics, and as a food additive – however, these uses come at a price. Only around 1-4mg of raspberry ketone can be extracted from a kilogram of raspberries, and as a consequence the cost of the naturally occurring compound is significant. Synthetic forms of the compound are, however, less costly.

In recent years, there’s been an increasing interest in raspberry ketone as an anti-obesity supplement. A study in 2005 found that mice given the compound showed increased breakdown of fat; the conclusions drawn from the study were that raspberry ketone could help prevent and improve obesity and fatty liver. However, it’s important to note that there have been no reliable, controlled tests in humans of this supposed anti-obesity action, so we have no idea if the same effects would be seen. The dosages of the compound used in rodent studies were also higher than would be obtained from the use of raspberry ketone supplements in humans.

One of the compounds that contributes towards the flavour of raspberries has also made it into the news in recent years – but for a very different reason. In 2009, astronomers searching the large dust cloud at the centre of our galaxy to try and detect complex molecules in space succeeded in identifying a number of compounds, including the compound ethyl formate. Ethyl formate smells of rum, and is one of a number of chemical contributors to the flavour of raspberries; this discovery spawned a number of news articles proclaiming that ‘space tastes of raspberries’.

The reality is probably a little more complex, and a little less raspberry flavoured. Whilst ethyl formate is indeed a contributor to raspberry flavour, a number of other complex molecules have also been detected in space, and the team examining the dust cloud at the centre of the galaxy identified at least 50 other molecular entities as well as ethyl formate. Ethyl formate is probably much less abundant compared to some of these; for example, the same dust cloud that ethyl formate was detected in contains a significant amount of methanol.

So, does the galaxy taste of raspberries and smell of rum? Whilst the ethyl formate is out there, it’s a little bit of a simplified view. Sadly, considering that the Sagittarius B2 dust cloud in which it was detected is around 25,000 light years from Earth, so we’re unlikely to be able to put the raspberry-flavoured theory to the test any time soon!



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