Facts about miracle fruit (miraculin revisited - part 2:2)

Short introduction in Norwegian: I anledning at jeg deltok i en episode om mirakelfrukt på Schrödingers katt på NRK (og YouTube) publiserer jeg to blogginnlegg om temaet. Det første innlegget handler om smakstesting av mirakelfrukt. Innlegget nedenfor er del 2 av 2 og er en samling fakta om mirakelfrukt med referanser til forskningslitteratur. Siden denne bloggen normalt er på engelsk fortsetter jeg herved på engelsk.

On the occasion of me attending an episode of the Norwegian popsci TV series "Schrödingers katt" (and YouTube) about miracle fruit I post two entries on miracle fruit and its key constituent miraculin. The first post describes a tasting of miracle fruit with a number of sour foods. The second post below is a collection of facts about miracle fruit based on research literature. Part 2:2 below is divided into the following main topics:

• Miracle fruit/berry - properties
• Traditional/historic use of miracle fruit
• Taste sensation when using miracle fruit/miraculin
• Cultivation and production
• Use in commercial products, potential applications
• Health risk and governmental/public approval
• Elimination of the sweet-inducing effect
• Mechanism of taste-modifying activity
• Some other sweet and taste-modifying substances
• References

Miraculin revisited - part 1:2

Introduction in Norwegian: I anledning denne ukas episode om mirakelfrukt på Schrödingers katt på NRK (og YouTube) publiserer jeg to blogginnlegg om temaet. Det første er en reprise av et tidligere innlegg, dog utvidet med noen flere smakstester. Det påfølgende er en samling fakta om mirakelfrukt med referanser til primærlitteraturen. Siden denne bloggen normalt er på engelsk fortsetter jeg herved på engelsk. Innlegg nr. 1 av 2 følger nedenfor.

On the occasion of me attending this week's episode of the Norwegian popsci TV series "Schrödingers katt" (and YouTube) about miracle fruit I'll post two entries on miracle fruit/miraculin. The first is a reposting on a previous entry, expanded with a few more tasting notes. The second post will be a collection of facts about miracle fruit including references to primary literature. Part 1:2 follows below.

The following entry was previously published 7 August 2010, slightly revised.
Note: the original blog entry has some interesting comments worth having a look at.

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For some time now, there has been somewhat of a hype about the miraculous berry that makes everything sour taste sweet. Some time ago, I ordered a packet of dried and powdered miracle fruit tablets and gave it a try. The following post gives some background and the results of a truly fascinating experience.

The miracle fruit is a a berry containing the glycoprotein miraculin with the unlikely effect that when your taste buds meet this substance, you taste sour foods as they were sweet. That is, your perception of sourness is altered. In certain parts of the world, the substance has been used for quite long, whereas in USA and Europe it has not yet been cleared for use as additive. The berry in itself is allowed, but unfortunately they don't keep for long and are apparently not suited for shipping fresh. However, a freeze dried version made into tablets does exist and this is the version I tried.

There is quite some amount of research on the effect and mechanism of miraculin on our tongue as a google scholar search for "miraculin" reveals. The first scientific report was in Nature as early as in 1968 (correction: first time published in 1965). There is also research indicating that other plants exhibit similar effects, such as curculin from the Curculigo latifolia plant. The miraculin protein structure shown here is taken from the Swiss protein structure homology-modeling service.*

Miraculin!

For some time now, there has been somewhat of a hype about the miraculous berry that makes everything sour taste sweet. Some time ago, I ordered a packet of dried and powdered miracle fruit tablets and gave it a try. The following post gives some background and the results of a truly fascinating experience.

The miracle fruit is a a berry containing the glycoprotein miraculin with the unlikely effect that when your taste buds meet this substance, you taste sour foods as they were sweet. That is, your perception of sourness is altered. In certain parts of the world, the substance has been used for quite long, whereas in USA and Europe it has not yet been cleared for use as additive. The berry in itself is allowed, but unfortunately they don't keep for long and are apparently not suited for shipping fresh. However, a freeze dried version made into tablets does exist and this is the version I tried.

There is quite some amount of research on the effect and mechanism of miraculin on our tongue as a google scholar search for "miraculin" reveals. The first scientific report was in Nature as early as in 1968. There is also research indicating that other plants exhibit similar effects, such as curculin from the Curculigo latifolia plant. The miraculin protein structure shown here is taken from the Swiss protein structure homology-modeling service.*

An ordinary google search gives various producers and web shops for buying the stuff. Adding to the fun are the conspiration theory-like suggestions (two refs.) of the sugar industry's ways of stopping miraculin approval in the USA since the product might reduce the population's consumption of sugar (which of course is beneficial for everyone except the sugar industry). There are also efforts being made on producing the miraculin glycoprotein using genetic engineering methods, and I guess the hope is that one might efficiently produce miraculin or a relative using common plants or organisms such as lettuce or E-coli bacteria (same as is done with production of other proteins/enzymes such as medicinal insulin or rennet for cheesemaking).

December issue of school science magazine on food

The last issue of the Norwegian science education magazine "Naturfag" (equivalent to "School science") has several articles on food previously posted here on fooducation. The magazine is in Norwegian and free for download.

Issue 2/2009 with mostly Christmas- and winter related content includes the following articles based on fooducation posts. Most of them are updated/revised versions and are also found as updated versions on the Norwegian Centre for Science Education "gastronomic school science" web pages www.naturfag.no/mat (Google translation here):

1. "Christmas dinner trimmings - a hot potato?" (part 1 and part 2) and "Green vegetables and chlorophyll revisited" combined
   
   
2. "Deciphering an old preserves recipe"
   
   
3. The effect of added sugar, salt and high temperature on microorganisms/yeast. This is not previously published on fooducation, but a time lapse video with captions in Norwegian can be seen on YouTube. It is self-explanatory, i guess. The purpose is to show an easy to set up experiment for testing conditions under which microorganisms thrive or die. Relevance is to baking (you want to promote the yeast) and preservation (you want to suppress or kill microorganisms)
   
   
4. "Leavens in cookies - theory and practice"

The latter also made it into the news section of "Nysgjerrigper", a science knowledge project from the Norwegian Research Council.

Of course there are several other interesting topics in the issue as well, such as "Gingerbread house architecture" "Catch sight of and predict the northern light" and more.

Merry Christmas

Green vegetables and chlorophyll revisited

"I am an imbecile! I see only half of the picture!"

...is one of my favourite quotes of Agatha Christie's famous detective, Hercule Poirot. After pondering for months about why the broccoli cooking water turns green when using slightly basic and not when the water is slightly acidic the answer was right beneath my nose all the time, and I felt exactly like beloved Hercule (see the posting "Christmas dinner trimmings - a hot potato? Part two").

The trick to cooking wonderfully green vegetables is using a pinch of baking soda (sodium bicarbonate) in the cooking water. Because the water then is slightly basic, the magnesium ion is retained in the chlorophyll, and the colour is a vivid green, see the above mentioned posting. Deliberately using some acid (vinegar) renders the vegetables dull olive green.

What puzzled me was that the cooking water turns green when the vegetables are the most green, whereas the water is completely colourless when the vegetables are dull. How come? For a long time my hypothesis was that the chlorophyll, or some of its derivatives, is extracted to the water when using baking soda, but not when using vinegar.

Earlier this autumn, during a kitchen lab lesson, it suddenly struck me that the chlorophyll (or a chlorophyll derivative) might be there all the time, but that it's invisible in the acidic water, and that seems indeed to be the case. In fact, it retains it's colour, being green in basic water, and colourless in acidic water (see Martin's comment in the Christmas dinner trimming post).

The ultimate test is to look for chlorophyll colour in the acidic water, and the most straightforward experiment was to add some base to the colourless cooking water, and voila: the water took colour! Rendering the solution acidic again by adding some more vinegar resulted in colourless solution, as seen from the video below.

So, this is an example of chemical reversibility: adding one ingredient (i.e. acid/vinegar) you push the situation one way, adding another (baking soda/ammonium chloride, neutralising the acid), you pull it back to towards the starting point.

What might be learned/taught
In my opinion, this adds some chemistry to the kitchen trick of cooking green vegetables with bicarbonate. Also, it provides a meaningful arena for teaching acid/base equilibria and naturally occurring indicators.

Some details
To be honest, in this case it's slightly more complicated than going straight forward and back, and the colour diminishes in going back and forth. Acid and base is added consecutively, whereas the magnesium ions that are responsible for the colour are constantly diluted. Also, adding acid/base introduces other ingredients (acetate/vinegar and sodium/ammonium ions from the base). Thus it's not an entirely pure back and forth situation. I guess, if I'd added magnesium ions together with the baking soda there should might have been a more distinct colour change . One of these days I'll have to do just that.

Finally, the world is usually more complicated than meets the eye. I might very well have missed a point or two somewhere along the way. But anyway; I'm content with this explanation, and the observation of reversibility adds another dimension to using this experiment with students.

Late addition
When chlorophyll (either structure, a or b) reacts with an acid, pheophytin is formed. This is also coloured, but more olive-green or yellowish , depending on whether it's the a or b form. It might very well be these, or derivatives thereof, that are seen in the water solution. There are loads of scientific publications on chlorophyll, of course. A paper of relevance to science education is found in J. Chem. Ed. (This, Valverde, & Vignolle).

Christmas dinner trimmings - a hot potato? (part two)

Many a Christmas dinner, we end up with the potatoes falling apart in the dish and pale olive-green Brussel sprouts. Does it have to be like this? Using a little scientific knowledge in the kitchen can help.

Part two - green vegetables
Brussels sprouts and the broccoli: Do you prefer a fresh, vivid green colour, or a dull olive green? The colour in green vegetables is due to chlorophyll, which is a compound well suited to play around with. The green colour in chlorophyll is due to a magnesium atom (in fact, an ion) attached to a porphyrin ring, and acid can substitute this magnesium altering the colour. Try adding a little lemon juice or vinegar to the water next time you cook green vegetables if you want to do a “sabotage experiment” just to see what you may want to avoid. This kind of sabotage experiments are, in my opinion, just as important as the “successful” ones.

Chlorophyll molecular structure at pH = 7 (neutral/basic) to the left, and pH<7

Fruit and vegetables contain a little acid, so if we use pure water or steam the, this acid is in fact sufficient to alter the colour in a negative way. As a remedy, try adding a couple of teaspoons of (sodium) bicarbonate/natron per litre of water. This makes the water slightly basic. The water will turn green as well, but there is more than enough chlorophyl left for the vegetables. Short cooking times is also recommended, as chemical reactions take time, and the replacement of magnesium is no exception. This is probably the reason that the colour change is more visible in Brussels sprouts than broccoli, the sprouts cook longer and thus more of the chlorophyll is degraded.

Left: cooked with a little bicarbonate (pH ca. 9), right with a little lemon juice or vinegar (pH ca. 4.5)

So, in the two posts conclusion: treat the potatoes and vegetables the opposite way.

Happy New Year

Erik

Background info:
McGee, H. (2004): McGee on Food and Cooking – An Encyclopedia of Kitchen Science, History and Culture. London: Hodder and Stoughton.
Belitz, Grosch og Schieberle (2004): Food Chemistry (3. utg.). Berlin: Springer.

PS: have any idea why the water turns green on adding bicarbonate? Please let me know.

Christmas dinner trimmings - a hot potato? (part one)

Many a Christmas dinner, we end up with the potatoes falling apart in the dish and pale olive-green Brussel sprouts. Does it have to be like this? Using a little scientific knowledge in the kitchen can help.

Part one - potatoes
In Norway, Christmas dinner is often accompanied, amongst several things, by boiled potatoes and Brussels sprouts. The potatoes are often of a mealy sort, and peeled before cooking rather than after.

Mashed potatoes are a result of the outer parts of the potato being cooked too much before the inner parts are tender. Potatoes contain pectin, the cement which holds the cells together. Pectin is soluble in hot water, and when mealy potatoes are boiled, the pectin dissolves in the water. The cement is gone, and the potato fall apart in it’s separate cells. There is, however, an enzyme in the potato that helps the pectin molecules to cross-link internally, so the pectin stays in the potato. This enzyme is active between 50 and 60 °C. The solution is: leave the potatoes in water at this temperature for 20-30 minutes before heating further up, and your potatoes will not fall apart (use a standard cooking thermometer). But beware; the cooking time will be longer. Cooking bacalhau a couple of weeks ago, I had a fascinating experience (in Norway it goes by the name bacalao. Bacalhau is a Portuguese/Brazilian fish dish, in this case a hot pot with tomatoes, potatoes, onion, clipfish, black olives and olive oil). The potatoes were pre-cooked as described above, peeled and cut in large pieces, and added to the hot pot. After 75 minutes simmering, the potatoes were still not tender, and the guests had to wait another 15 minutes. One and a half hour’s simmering before the potatoes were tender! The potatoes, by the way, kept their shape perfectly even when the dish was reheated.
If you deliberately want the potatoes to fall apart, i.e. to thicken soup, you should do the exact opposite: put the pre-peeled potatoes directly in boiling water.

One problem with such pre-cooking is the off-colour (enzymatic browning). This can be fixed by adding a little acid, a tea spoon of vinegar or some lemon juice, or an antioxidant; a C-vitamin tablet or a tea spoon of pure ascorbic acid does the trick. The acid retards the reaction, while the ascorbic acid (C-vitamin) sacrifices itself in the reaction.

A drawback is that vitamin-degrading enzymes are also efficient at temperatures between 50 and 60 °C, so focusing on texture results in lower vitamin content. For everyday dinner I’d put unpeeled potatoes directly in boiling water to deactivate the vitamin-degrading enzymes, alas deactivating the pectin reinforcing ones as well.

Part two will deal with the Brussel sprouts - how to achieve a fresh green colour rather than a pale olive-green colour. A Norwegian version of this post can be found at www.naturfag.no/mat.

Merry Christmas(-dinner)

Erik

Background info:
McGee, H. (2004): McGee on Food and Cooking – An Encyclopedia of Kitchen Science, History and Culture. London: Hodder and Stoughton.

Tomato foam

The Norwegian cook, food writer and weekly source and inspiration (at least to me) Andreas Viestad wrote a fascinating piece on tomato mousse:
Run a tomato or three (cut in pieces) in a blender for five minutes. Running for a shorter time will not give the desired result even though it seems finished. Pour into a bowl and leave for a few hours and you get a mousse-like pink jelly. With reference to prof. Hervé This he guesses that the reason may be liberation of pectin from the crushed tomato skin. Pectin is a natural occurring acidic polysaccharide/carbohydrate which contributes to stiffness in some fruit/berry jams and jellies.

I tried this with moderately satisfactory result; a fairly ok foam/mousse on the top with a more soggy mass at the bottom of the glass.

SUGGESTIONS ON WHY THIS DOES WORK (or not work) AND EXPERIMENTS TO TEST THE HYPOTHESES
If pectin is the big point
- using ripe tomatoes should give poorer result that unripe (or less ripe) as the pectin is broken down during ripening. This is by the way the reason why you should use not very ripe berries/fruit when making jam/jelly and more ripe when making juice/syrup. Vice versa: ripe/unripe tomatoes should not make a difference if pectin is not involved.
- Pectin is located in the skin, cell walls and between cells of the tomato. Breaking the cell walls (destroying the cells) by blending should therefore not be a critical point.

If breaking the cells walls is of vital importance
- freezing the tomatoes should be very effective in breaking the cell walls as expansion and formation of sharp crystals by loads of water inside the tomato will cut/explode the cells from within. After freezing, long blending time should not be necessary. Why this should be, I'm not sure. A biologist colleague meant that a possible reason may be that enzymes within the cells are liberated and can react with other parts of the tomato.

Suggested (comparative) experiments:
For consistent experiments, the same blender speed should always be used, and the container should be rinsed between each blending. Washing unnecessary? (most of the tomato is water soluble, but important compounds may be water insoluble)

1) Blending time - cut four tomatoes in two and divide in two heaps (two halves from the same tomato in each group). This way, I'll have to identical heaps. Run one heap for 1-2 minutes, the second for at least 5 minutes. Pour into separate bowls and leave for a few (3-5?) hours.

2) Breaking cell walls - cut four tomatoes in two and divide in two heaps as above. Put each heap in a plastic bag, leave one in the fridge and the other in the freezer overnight. Thaw the frozen tomatoes and run each heap in the blender for an identical period of time. Pour into separate bowls and leave for a few (3-5?) hours.

3) Ripe vs. unripe and blending time double experiment - this is a little less stringent that the point above, but worth a try. You need ripe and unripe (less ripe) tomatoes, ideally from the same plant (grow your own). Make four heaps:
a1) Ripe + short blending time
a2) Ripe + long blending time
b1) Unripe + short blending time
b2) Unripe + long blending time
Run the four heaps separately as for 1). Pour into separate bowls and leave for a few (3-5?) hours.


I'll have to follow up this some time soon (maybe wait for our own tomatoes to ripen?). Results and reflections will be published.

Erik

Addition 11. May 2010: Report from The Flemish Primitives 2010 by Martin "khymos" Lersch has some interesting and possibly relevant info on this matters as well as references. Maybe a solution is to be found therein?