Sweet and Sour Science

Japanese researchers unravel the mystery of miracle fruit.

By | February 1, 2012

image: Sweet and Sour Science MAGIC BERRIES: The miracle fruit, Synsepalum dulcificum, grows wild in tropical West Africa.Satoshi Okubo

MAGIC BERRIES: The miracle fruit, synsepalum dulcificum, grows wild in tropical West Africa.SATOSHI OKUBO

Imagine sucking on a lemon that tastes as sweet as honey, or munching on what you think is a crunchy candy only to discover it’s a pickled onion. Such is the taste-bud trickery experienced at so-called flavor-tripping parties. The secret to the flavorful deceptions is a small red berry from West Africa called miracle fruit, which itself has very little flavor, but can make sour or acidic foods taste extremely sweet when eaten soon after the berry contacts the tongue. So bizarre is the fruit’s effect that just one taste was enough to convince Japanese food scientist Keiko Abe, of the University of Tokyo, to launch into an entirely new area of study.

In the early 1980s, Abe was researching oryzacystatin, the first recognized plant protease inhibitor, which she had identified and cloned from rice. But, one day in 1989, Yoshie Kurihara of Yokohama National University, who worked on miracle fruit and had managed to successfully cultivate the plant, visited Abe’s lab. She brought with her miracle fruit and lemons.

"Eating the fruits, I was surprised and excited,” says Abe. “The sourness [of the lemons] disappeared.”

“It made me change my interest from protease inhibitor biochemistry to taste science,” she adds. “Since then, I have been working on taste chemical biology.” Abe focused specifically on miraculin, the protein in miracle fruit responsible for its flavor-transforming powers.

More than twenty years after her first taste of the berries, Abe has finally exposed miraculin’s trick. “At long last, my group succeeded in unveiling the molecular mechanism that makes miraculin a miracle,” she says.

ADREZEJ KRAUZE

Previous studies had shown that inhibitors of the human sweet taste receptor could diminish miraculin’s effect, but there was no formal proof that the protein and the receptors interacted. Furthermore, a mere ability to bind the receptor wouldn’t explain why miraculin didn’t taste sweet on its own but rather made acidic compounds taste sweet.

Abe and her team expressed the sweet taste receptor in cultured human cells and then observed miraculin’s function using fluorescence to measure intracellular calcium concentrations, which increase when the receptor is active. At neutral pH in miraculin’s presence, calcium levels inside the cells remained low. At acidic pH, however, the cells fluoresced brightly.

Although miraculin didn’t activate the receptors at neutral pH, it was still bound and could inhibit their activation by other sweeteners. “So the miraculin has been sitting there, it’s ready to go, but it is not actually turning the key to turn on the sweet taste receptor, and therefore you’re not getting a perception of taste,” says Steven Munger, a chemosensory neurobiologist from the University of Maryland School of Medicine. “Adding the acid changes the shape of the miraculin, and that in turn changes the shape of the receptor, which turns it on.”

Using their in vitro model, Abe’s team also determined the precise part of the receptor with which miraculin interacts. They now plan to determine the X-ray crystallographic structure of that interaction. They also hope to use miraculin to answer further questions about sweet taste receptor biology. As taste biologist Paul Breslin of Philadelphia’s Monell Chemical Senses Center and Rutgers University points out: “It is very hard to study sucrose in an in vitro system because it is sweet at such a high concentration relative to things like miraculin . . . and those high concentrations tend to osmotically muck everything up.”

“The sweet taste receptor-binding ability of miraculin is stronger than that of any other sweetener known,” says Abe. Besides being an interesting phenomenon, this strong binding makes miraculin a “calorically negligible” sweetener says Munger. Consequently, Abe says, “We are interested in a large-scale production of miraculin . . . because developing sweeteners for antidiabetes and antiobesity uses is of pressing importance.”

Besides the need to solve the logistics of cost-efficient, large-scale production, some modifications might need to be made to miraculin before it is used as a food additive. “The sweetness is very long-lasting,” explains Munger. In fact, it can last up to a couple of hours.

Munger has first-hand experience with this problem of sustained receptor binding. “The first time I ever tried it was at a smell and taste meeting in Japan . . .but unfortunately, the session was followed by a social hour where there was beer.” There is enough acid in beer to trigger the miraculin, Munger explains. “It tasted very wrong.”

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Comments

Avatar of: agelbert

agelbert

Posts: 50

February 13, 2012

Let's hope toxicity studies are more thorough on this brave new sweetener than the rush jobs done for saccharin and equal.

Antifreeze is quite sweet and has caused the death of many animals that like the sweet taste (dogs are the main victims) as well as some humans.

And what about the danger of altering our ph balance from consuming a low ph substance masked by this sweetener?

Avatar of: Procrastibaking

Procrastibaking

Posts: 1457

February 13, 2012

From my experience with this berry, you are still able to feel the after effects of consuming low pH food when it moves towards the stomach. You would still be able to tell what you're eating is acidic, just not via normal tastant interactions on the papillae.

Avatar of: James Kohl

James Kohl

Posts: 53

February 13, 2012

If mixtures of species specific pheromones activate olfactory receptors in a similar manner, which also affects perception, it might help to explain the difficulty in identifying a human pheromone. Perhaps the singular term: pheromone, is merely a semantics problem given the likelihood that human pheromones (plural), like the pheromones of other species, also exist. It could also be that classically conditioned hormone responses to pheromones, which are associated with other sensory input from the environment, are typically conditioned only in the presence of more than one pheromone. 

Avatar of: James Kohl

James Kohl

Posts: 53

February 13, 2012

More speculation: The combined effects of predator pheromones and the endocrine disruptor atrazine appear to be more potent than their separate effect on anuran species. If the combined effect of insecticides and pheromones in honeybees was the cause of colony collapse, it would be much more difficult to determine from examination of any suspected singular factors.

Avatar of: Hello

Hello

Posts: 1457

February 13, 2012

What happens if you eat something sweet soon after eating the berry? Does it taste even sweeter.

Can these be grown indoors in Canada?

Avatar of: Procrastibaking

Procrastibaking

Posts: 1457

February 13, 2012

In my experience, no, sweet things don't taste sweeter after eating the berry. Sweet things that have a sour note to them, however, become sickly sweet.

Avatar of:

Posts: 0

February 13, 2012

Let's hope toxicity studies are more thorough on this brave new sweetener than the rush jobs done for saccharin and equal.

Antifreeze is quite sweet and has caused the death of many animals that like the sweet taste (dogs are the main victims) as well as some humans.

And what about the danger of altering our ph balance from consuming a low ph substance masked by this sweetener?

Avatar of:

Posts: 0

February 13, 2012

From my experience with this berry, you are still able to feel the after effects of consuming low pH food when it moves towards the stomach. You would still be able to tell what you're eating is acidic, just not via normal tastant interactions on the papillae.

Avatar of:

Posts: 0

February 13, 2012

If mixtures of species specific pheromones activate olfactory receptors in a similar manner, which also affects perception, it might help to explain the difficulty in identifying a human pheromone. Perhaps the singular term: pheromone, is merely a semantics problem given the likelihood that human pheromones (plural), like the pheromones of other species, also exist. It could also be that classically conditioned hormone responses to pheromones, which are associated with other sensory input from the environment, are typically conditioned only in the presence of more than one pheromone. 

Avatar of:

Posts: 0

February 13, 2012

More speculation: The combined effects of predator pheromones and the endocrine disruptor atrazine appear to be more potent than their separate effect on anuran species. If the combined effect of insecticides and pheromones in honeybees was the cause of colony collapse, it would be much more difficult to determine from examination of any suspected singular factors.

Avatar of:

Posts: 0

February 13, 2012

What happens if you eat something sweet soon after eating the berry? Does it taste even sweeter.

Can these be grown indoors in Canada?

Avatar of:

Posts: 0

February 13, 2012

In my experience, no, sweet things don't taste sweeter after eating the berry. Sweet things that have a sour note to them, however, become sickly sweet.

Avatar of:

Posts: 0

February 13, 2012

Let's hope toxicity studies are more thorough on this brave new sweetener than the rush jobs done for saccharin and equal.

Antifreeze is quite sweet and has caused the death of many animals that like the sweet taste (dogs are the main victims) as well as some humans.

And what about the danger of altering our ph balance from consuming a low ph substance masked by this sweetener?

Avatar of:

Posts: 0

February 13, 2012

From my experience with this berry, you are still able to feel the after effects of consuming low pH food when it moves towards the stomach. You would still be able to tell what you're eating is acidic, just not via normal tastant interactions on the papillae.

Avatar of:

Posts: 0

February 13, 2012

If mixtures of species specific pheromones activate olfactory receptors in a similar manner, which also affects perception, it might help to explain the difficulty in identifying a human pheromone. Perhaps the singular term: pheromone, is merely a semantics problem given the likelihood that human pheromones (plural), like the pheromones of other species, also exist. It could also be that classically conditioned hormone responses to pheromones, which are associated with other sensory input from the environment, are typically conditioned only in the presence of more than one pheromone. 

Avatar of:

Posts: 0

February 13, 2012

More speculation: The combined effects of predator pheromones and the endocrine disruptor atrazine appear to be more potent than their separate effect on anuran species. If the combined effect of insecticides and pheromones in honeybees was the cause of colony collapse, it would be much more difficult to determine from examination of any suspected singular factors.

Avatar of:

Posts: 0

February 13, 2012

What happens if you eat something sweet soon after eating the berry? Does it taste even sweeter.

Can these be grown indoors in Canada?

Avatar of:

Posts: 0

February 13, 2012

In my experience, no, sweet things don't taste sweeter after eating the berry. Sweet things that have a sour note to them, however, become sickly sweet.

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