Don, Norwich asked:
I was wondering what limonene is and what itís used for?
Chris - Brilliant. Yeah, well limonene, itís the stuff that makes oranges and lemons smell orangey and lemony. So, if you take an orange and you scrape the peel a little bit and smell your fingers, itís that very intense orangey citrus smell, isnít there?
Don - Yeah.
Chris - And that is the limonene. The orange peel contains huge amounts of it. Itís a very big organic molecule. Itís lots of carbon and hydrogen atoms stuck together in giant ring structures. And in fact, we did an experiment on The Naked Scientists a little while back. Dave did it as a Kitchen Science where you actually blasted some of the limonene through a candle by squeezing the peel of the fruit and you spurted the limonene into the flame.
Dave - Thatís right. You produce a sort of aerosol of limonene into the flame and limonene is really flammable and so, it catches fire.
Chris - But the reason that fruit makes it is because itís also quite nasty for things other than humans who havenít got fingers to peel an orange. If you try to borough through the peel of an orange, youíd have to eat the peel and the peel doesnít taste too good. Limonene is mildly toxic and being organic and unpleasantly tasting as it is, it puts off insects and thatís a way that the tree uses of keeping its fruit in good condition.
Don - Okay. I find it also in my shower gel. Why is it in there?
Chris - Sure. Well the answer is rather than trying to invent artificial flavours and colourings and things which would do the same job as a molecule which is already doing the job very well in nature, sometimes itís easier just to use the natural product and then you can also have a marketing benefit because you can say, ďHey! This is a natural product. Itís got limonene in it.Ē So, rather than having to use orange flavored stuff or a small molecule that smells the same, then you can just use the natural product and then you get two bangs for your buck. So, what itís doing in your shampoo is contributing a nice orangey aroma and which also, because itís fatty and oily, it will stick to your skin quite well. It wonít get washed off by the water and it leaves you smelling vaguely with a faint aroma of oranges. Have you noticed that?
Don - Yeah. I have.
Chris - Then weíve got the answer right. Thank you very much, Don.