Smell and chemoreceptors. Stereoisomers and enantiomers. Noses and brains. And when life gives you lemons, make oranges!
1-Minute NomNom
If someone asked you, “Why do you smell?”, what would you say? If I were you, I would reply, “I smell because of volatile compounds and spatial arrangement!”
WhaaaaAaaaattt??!!
Yup, that is right. When volatile chemical compounds i.e odorants stimulate our chemoreceptors or receptor cells – cells that can sense chemical compounds – in our noses (see diagram above), these chemoreceptors send signals to our brains to identify the smells (read why we became nosey to survive in the 1-Minute NomNom “Nose job“).
As each chemical compound has its own 3D shape and structure, it will trigger a unique set of chemoreceptors. That means each chemical compound has its peculiar smell (it is a bit like how a specific key fits with a specific lock, and not others).
A small difference in structure is all that is needed for smells to be different. For example, the orangey smell in our dishwashing liquid is from a chemical compound called D-limonene (C10H16). Keep the chemical formula but tweak its 3D shape and structure a little, and it becomes L-limonene, which smells like pine instead!
The difference can even be very subtle. This is clearly demonstrated by D-limonene and L-limonene, which are in fact enantiomers.
What are enantiomers? When two chemical compounds have the same chemical formula but have different structures, they are called isomers of each other i.e. same formula, different arrangement. When this difference in structure is in 3D-space , they are called stereoisomers i.e. same formula, different 3D arrangement. When two stereoisomers are a mirror image of each other, they are called enantiomers.
Do you prefer my smell or my mirror image’s?
Each enantiomer stimulates different chemoreceptors. D-limonene, which comes from oranges and lemons, stimulates the chemoreceptors that make us smell orange, while L-limonene, which comes from pine cones, stimulates those that make us smell pine. All it took was for them to be mirror images (imagine if you and your mirror image smelled different!).
Interesting fact: to produce D-limonene, we just need to extract and distill it from orange and lemon rinds. Which is why if life gives you lemons, don’t just make lemonade; make orange aromas too!
Feed Me!
What is your favorite fruity scent in the kitchen? Share it with us in the comments below!
Orange you glad you liked me, so you can discover more? All you need is a minute a day to explore the world’s marvels through the phenomenon of food!
photos: in order – istockphoto/Lvnel; depositphotos/edesignua; newlight; ls992007 ; HASLOO; HASLOO
