Issue 17 December 2001 ( PDF )

The sweet side of life

by Vivienne Baillie Gerritsen

There are four basic tastes…so we are told. Any other taste is a mere combination of these four. Which four? Bitter, sweet, sour and salty. However, a fifth taste – of Asian heritage – is seeping into the Western World and gaining fast recognition: the umami (oo-mom-ee) taste. A taste qualified as meaty or savoury. All these tastes are recognised as such thanks to specific taste receptors and our brain. Some tastes are proteins and are already used in the industry as natural sweeteners, for example. Among such taste proteins, there is one in particular – miraculin – which lacks taste completely when absorbed on its own but has the power of modifying a disagreeable taste into a pleasant one.

Miraculin is a rogue. Here is a protein which manages not only to shield a sour taste but also to make you believe that what you are eating or drinking is actually sweet! It is a 190 amino-acid glycoprotein and known as a super sweetener. Indeed, purified miraculin contains almost 14% sugar: glucosamine, mannose, galactose, xylose and fucose. It is found in the pulp of the fruit of the miracle berry, otherwise known as Richadella dulcifica or Synsepalum dulcificum, an evergreen shrub native to tropical West Africa.

The red fruit bears a single olive-shaped seed, is about 2 to 3 cm long, and is quite tasteless. But coat your tongue with the pulp of this fruit and you can swallow a litre of vinegar followed by a kilo of lemons without a wince. And the effect can last up to two hours. You will not be spared the consequences of so much sourness though and crops of ulcers will flourish. Anyway, who wants to drink vinegar and eat lemons? The issue is that the consumption of a miracle berry will modify a sour taste into a sweet taste. It is something the West Africans have long known and for years they have been using it in food and beverages to suppress sourness.

[ Richadella dulcifica and its red berries ]

Richadella dulcifica and its red berries.

Courtesy of Ken Love

The protein itself was extracted in the 1960s and named miraculin after its miraculous powers. To understand how it works, you need to know the anatomy of a tongue. Our tongue – like all mammal tongues – is coated with papillae of different shapes and sizes. Within each papilla is wedged a taste bud, itself a haven for 50 to 100 taste receptor cells. These receptor cells bear taste receptors on their membrane that open ion channels once activated, which in turn transmit a taste message to the brain. Each taste has its receptor, i.e. a salty taste will activate the salty receptor and elicit a salty taste. So how does miraculin – which has no taste – elicit a sweet taste when it is, in effect, a sour one? Well…it tricks the brain by fooling the sweet taste receptor.

A structural model of the sweet-inducing protein and its binding to the sweet receptor has been suggested. Miraculin may bind to sweet receptors although, in the absence of sourness, its active site does not. As a result, there is no sweet taste. However, when sour substances are presented to our tongue, the sweet receptors undergo a conformational change and, in doing so, give miraculin the opportunity to reposition its active site within the sweet receptor. The net result is a strong sweet taste in the mouth. And since miraculin binds particularly firmly to the receptor, the sweet fib can last a maximum of two hours. It is said that the actual taste of the food is kept yet the sourness is warded off. Hence, a slice of lemon would taste like lemon candy.

In a day and age when ‘natural’ substances are seated in the front row, miraculin could well have a bright future by replacing synthetic sweeteners already widely used. Pop a miracle berry into your mouth and the taste of low calorie sour food or beverages becomes bearable. Diabetics could also benefit from the effects of miraculin. The snag is production at the industrial scale. Richadella dulcifica – like so many other plants – is very particular as to the conditions in which it grows. What is more, protein purification directly from the plant is expensive. The expression of miraculin in recombinant hosts is being looked into although – so far – it has not met with much success mainly because it is very difficult to preserve the taste modifying properties of the naturally occurring miraculin protein. To turn a long story sweet can be a sour affair.

References
1. Faus I.
Recent developments in the characterization and biotechnological production of sweet-tasting proteins.
Appl. Microbiol. Biotechnol. 53:145-151(2000).
PMID: 10709975

2. Kurihara Y.
Characteristics of antisweet substances, sweet proteins, and sweetness-inducing proteins.
Crit. Rev. Food Sci. Nutr. 32:231-252(1992).
PMID: 1418601

3. Witty M.
Proteins pack muscle to modify taste.
http://www.preparedfoods.com/archives/1999/9905/9905proteins.htm
Swiss-Prot cross references
Miraculin, Richadella dulcifica : P13087
Need to reference this article ? Please use this link:
<http://web.expasy.org/spotlight/back_issues/017/>

Comments

Great article, and thank you for your insights into this most extraordianry fruit.
Thanks again!
Bill

Posted by Bill Turner on Monday 11 July 2005 3:05 CET

I looked for a Miracle Fruit Bush for about five years and finally found one in the Pembroke Pines Nursery in Davie, Florida. I planted it and receive an abundant yearly crop of berries which I put into the freezer. Contrary to what I have read, the frozen berries work just as well as the fresh ones. I have found that the berries also affect the taste of tomatoes and vinegar. If you would like a sweeter taste to your vinegar-based dressing for your salad just pop a berry into your mouth before eating. I am presently attempting to grow some new bushes from seed. Regards, Don Aldridge

Posted by Dop Aldridge on Tuesday 22 August 2006 14:23 CET

I just recently found out about this particular plant and its taste-modifying protein. So I tried to read up on it as best as I could. I was a little disappointed that I could not find anything written about the actual biological role that miraculin plays. Even the Swiss-Prot reference only says that its function is to modify a "sour taste into a sweet taste."
Does anyone know of any research or even speculation as to why there is a protein like this in nature? At first glance, it would seem to me that it would place this plant at a severe evolutionary disadvantage, because an herbivore might eat the berries, then eat the rest of the plant, thinking it was sweet and had "high nutritive content".
Although, maybe the strategy is to get the herbivore to eat your berries, then go over to the competitor plant next to you and eat it, thinking IT is sweet... The drama is killing me inside....

Posted by Matt Tomcik on Monday 29 January 2007 6:07 CET

Found this online, some new research:

"However, recent Italian research on the taste cell-related diffuse chemosensory system (ref. 12) (DCS) may give a clue to what else could be happening. In humans, the sense of taste is transduced (ref. 13) by taste buds (ref. 14) and is conveyed via three of the twelve cranial nerves. Therein ‘taste buds’ are referred to as ‘classic’ taste organs, but it is argued as conceivable that this is the tip of the iceberg, that there is a ‘submerged’ portion with most of the iceberg more [caudally] located in the form of solitary chemosensory cells or chemosensory clusters i.e. the taste buds are probably only the most visible portion. In other words, what you see isn’t only what you get, that there are other less obvious chemoreceptive sensors that are not visible. While taste is defined as being sweet, sour, bitter, salty, and unami (savouriness), an analogy of a deep effect upon taste could be like e.g. biting into a chili pepper; as a taste it registers as spicy ‘hot’, but the chemicals in it can act as a temporary anaesthetic in the mouth giving a ‘numbing’ sensation that has been ‘received’ by chemoreceptors and transduced to give us that ‘sensation’ – there is more than one effect going on. When it comes to the Miracle berry there is certainly something different or unusual happening between its chemicals, our chemo-reception followed by our neuro-perception messaging that can transform ‘sour to sweet’. It is a conundrum!"

Hope it helps ... its a new view on this.

Dave

Posted by Miracle Fruit on Monday 31 May 2010 3:13 CET

I try in one large breath to drink 2 tablespoons of raw apple cider vinegar with 1/2 cup of water and an added sweetener to mask the awful bitter taste of the RACV to help my arteries, while holding my nosed pinched and then gulping down another cup of water and chewing gum SOOO I do not have to taste the bitter taste of RAV, IF, this works....I will be so happy to take my RACV.
Saw this on Dr. Oz...thanks

Posted by marlene on Saturday 19 February 2011 4:07 CET

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