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Last summer, I unexpectedly spent a rainy afternoon devouring a heaping pile of raw lemons, limes, and grapefruit with a giddy smile. I was determined to have an adventure in the rugged Colorado wilderness, so I joined a group of friends at an isolated hut in the mountains, where we enjoyed a weekend of hiking to amazing views, vibrant shooting stars, and “flavor tripping.”

Never heard of flavor tripping? I hadn’t either – and I wasn’t entirely on board with the idea of any kind of “tripping.” (I am, after all, a nerdy scientist.) But after reading the packaging of the mysterious “miracle berries” we were about to consume, my anxiety abated. This was just science! Allow me to explain.


Miracle berries are the fruit of a bushy plant native to West Africa. The berries themselves don’t have much flavor – just a pulpy white flesh and a dark brown pit. I should note that buying actual berries is difficult, and they don’t keep well. However, tablets made from miracle berries are easy to find. Both the berries and the tablets contain the miraculous ingredient: a protein appropriately dubbed miraculin.

Miraculin is a very special type of protein. When you chew a berry or dissolve a tablet on your tongue, miraculin binds to only sweet receptors on taste buds, where it works its miracles. The result: miraculin makes sour or acidic flavors taste sweet. When normally you’d be puckering uncontrollably from the sour taste of citric acid found in lemons, miraculin sends your brain signals of the most delightfully sweet lemonade you’ve ever tasted. Gone are the days of playing “lemon mouth” – you could eat lemons all day! Limes, grapefruit, pineapple, strawberries, oranges, watermelon – each one tastes like the most gloriously ripe fruit that you’ve ever tasted. As if the Elixir of Life were bestowed upon it, miraculin brings the fruit to its full potential, to burst forth with the sweetness of candy into your greedy mouth…

Okay, enough with the food erotica. This is a science blog, remember?

miraculin dimer

Crystal structure of the miraculin dimer, from Wikipedia

When exposed to an acid, like lemon juice, miraculin triggers sweet receptors to send a signal to your brain. The sweet signal miraculin produces is so strong, it overpowers other flavor signals (sour, salty, umami) that may also be transmitted. This type of protein is called an agonist because it activates the cell’s receptors, causing a signal to be sent out. However, miraculin acts as an agonist only at acidic pH – at neutral pH it is an antagonist, blocking the sweet receptors it is bound to.

Other foods have very altered flavors, too – try hot peppers, cheese, vinegar, tequila, beer, and wine. Foods that contain little or no acid, like chocolate and bread, will have pretty much no effect.

Miraculin has been researched as an artificial sweetener, but it is difficult to produce in mass quantities and becomes inactive when heated during cooking or baking. It also only changes the perception of taste, therefore you might get a stomach ache after voraciously devouring a few dozen lemons and limes. And, because miraculin binds very strongly, your altered sense of taste will persist for twenty minutes to an hour – not ideal for a simple sweetener.

In the end, I got my Colorado mountain adventure – but it wasn’t at all what I expected! Are you ready to experience fruit like never before? It’s National Watermelon Day – why not give it a try?

By Amanda Grennell

Posted by Science Buffs

A CU Boulder STEM Blog

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