How Miraculin Turns Sour Foods Sweet on the Tongue

Student Summary by Audrey Kim

Original Source: Jennifer Welsh — LiveScience, September 26, 2011https://www.livescience.com/16230-miracle-fruit-taste-sweet-sour.html

Image created by Audrey Kim

Abstract

Background: The "miracle berry" is a fruit that can turn sour taste into sweet. It possesses a protein called miraculin, which changes the function of our tastebuds and attaches to the sweet-sensing receptors. The impact is strong, making sour lemons taste like an extra-sweet lemonade. The effects of this red berry can last for an hour, and are also used often in flavor-tripping parties.

Objective: Researchers wanted to understand more about how these berries make sour taste sweet.

Method: To figure out how it works, researchers studied the interactions between miraculin and lab-grown cells engineered to make either the human or the mouse version of the sweetness receptor. Since mice do not respond to miraculin but humans do, the researchers compared the human and mouse versions of the receptor. Any part that differed between them was a candidate for where miraculin acts. This allowed the researchers to see which parts were important for sending the sweetness signals, and that way they isolated an area where the miraculin might bind to and cause the sweetness effect.

Results: Miraculin itself tastes flat, but under acidic conditions, it changes its molecular structure so the bind on the receptor becomes much stronger. It was found that miraculin worked differently than other known sweeteners like the sweeteners in diet sodas, which bind to another area in our sweet receptors. In the presence of acid (sourness), miraculin bound to the receptor a million times stronger than the artificial sweetener aspartame and 100 million times stronger than sugar. The stronger the compound bound, the sweeter it was.

Conclusion: Researchers are currently trying to "grow" these proteins by designing other fruits or vegetables that are able to produce them. This could help develop better artificial sweeteners in the future.