Raspberry flavour

The supermarket where I buy much of my shopping do an interesting line in budget cakes. Some of them are really poor quality, but others are not so bad and they are ideal for over-running grad students! I quite like the Raspberry Flavour Tarts. These are jam tarts with red jam and they do taste of raspberry BUT the ingredients listing makes it clear that they have never so much as waved to a raspberry from a distance. There is some apple as well as the usual gelling agents and preservatives and that old stalwart glucose-fructose syrup, but the flavour comes from just 'flavouring'. Today I've discovered what this mystery compound probably is.

Meet 'raspberry ketone' aka 'rheosmin' aka 4-(4-hydroxyphenyl)butan-2-one.

Apparently this is what they add to get a raspberry flavour. Being a good synthetic chemist it doesn't bother me in the least that chemicals are added to my food, since I'm well aware that 'natural' ingredients are just cocktails of chemicals anyway. I do, however, still find it fascinating that such a small molecule can give rise to such a distinctive taste. It's a 10-carbon unit and hence probably a biosynthetically produced as a monoterpene with post-condensational aromatisation.

A little gentle googling informs me that it's a white crystalline solid (though if I made it I'd probably end up with a yellow oil!), it is insoluble in water (but soluble in fats and alcohols) and the taste threshold is 40 ppm. It is apparently a major component of real raspberries (Rubus idaeus) and has been shown to be an effective anti-obesity drug - which seems like a good excuse to keep eating cake!

Next time you see 'Raspberry Flavour', think raspberry ketone!