This lovely little molecule is dopamine. It’s manufactured in your body from the amino acid L-tyrosine and is a precursor to adrenaline. I’m rather fond of dopamine, and I daresay so are you. Whoever you might be. You see, dopamine is a neurotransmitter and it’s actively associated with the pleasure system in the human brain. Anytime you do something that feels good, your brain releases dopamine (specifically, from areas such as the nucleus accumbens and prefrontal cortex).
Dopamine is responsible for you enjoying everything from cake to sex. In fact dopamine release is why people can find themselves with so many unusual behavioural addictions like gambling, shopping and video games. Worryingly, even aggressive behavour has been shown as a possible cause of dopamine release. Long story short, if something makes your brain release dopamine, it feels good. If it feels good, your brain is hardwired to make you seek more of it.
Mind you, dopamine has a whole host of other neurological functions too, playing a role in things such as working memory, learning, cognition and attention. But then, this wasn’t intended to be a post about neurochemistry. There’s a place other than inside your brain that you can find copious amounts of dopamine. You just need to look in your kitchen*.
When you cut fresh fruit, it normally turns brown. Apples, pears, aubergines and many other fruit undergo this change. This is because those fruit contain a combination of 1,2-diphenols and polyphenol oxidase enzymes. When you cut or bite into the fruit it exposes those chemicals to the air. The enzymes then use molecular oxygen from the air to oxidise the diphenols into quinones. This sets off a chain reaction, where the same quinones spontaneously oxidise further, before polymerising and condensing with amino acids, forming melanins. The end result is that if you bite into an apple and then put it down for a few minutes, it’ll turn that familiar brown colour. Naturally, it’s thought that those quinones and melanins are to protect damaged fruit from bacteria and fungi which might eventually kill off the seeds contained within. The exact same process, incidentally, is responsible for the brown colour of coffee and chocolate.
The interesting thing is that dopamine contains a 1,2-diphenol group. In fact, dopamine is the active diphenol in bananas! They’re full of it. Every time you see a banana that’s turning brown? Dopamine. I wouldn’t rush out and buy lots of bananas hoping for a neurochemical rush, mind you, as dopamine isn’t capable of passing the blood-brain barrier. All the same, bananas are a good source of potassium and various vitamins. You should go out and get some. They’re nice.
So if you’re chopping fruit and you don’t want it to go brown, the best thing to do is to denature the enzymes. Enzymes only work within a specific set of pH and temperature conditions. In short, dipping the fruit in something acidic like lemon or pineapple juice should be enough to denature the enzymes at the surface and at least slow down the browning process.
* You do have fresh fruit in your kitchen, don’t you?
Image credit: Wikimedia User:Darkone