The Chemistry of Chocolate

The “Blissful Joy” of chocolate is one enjoyed by mostly everyone. Ever since childhood people have been enraptured with its rich creamy taste and it has become a staple buy for people’s presents, children’s parties, cooking, dining and many more. This substance although it was first brought back by Christopher Columbus, has more recently formed a booming, multi billion pound industry with almost 660,900 tonnes of chocolate consumed in Britain each year.

Although seemingly simple, Chocolate making is a complex process containing a large amount of Chemistry. The main (and most expensive) ingredient of Chocolate is cocoa butter which is made up of triglycerides such as “1,3-distearoyl-2-oleoylglycerol”, more commonly known as “SOS”.

SOS forms 6 crystalline structures and it is crucial in chocolate making that only one of these structures (a structure known as “B(V)” )  is made. To get over this problem, producers use a method called “tempering” which effectively controls the temperature at which the crystal structure forms. Since each type of crystal is formed at a different temperature, this is a way of controlling and forming B(V). The cocoa butter is heated to a very high temperature in order to break down all 6 crystalline structures. Then the mixture is cooled to below 34 degrees (B (V)’S melting point) and kept at around 30 degrees to stop other crystals forming at lower temperatures. It is this particular Crystalline structure in chocolate that allows for its smoothness and texture, in fact you will notice that if you melt chocolate when cooking that the product you obtain when cooled will be different from the starting chocolate in taste as well as texture and this is because of the different crystalline structure that will have formed.

However, there is more than just heating to obtain the perfect structure needed for Chocolate. B(V) is not the most stable of structures and will often want to change to a lower energy state such as B(IV). This is obtained when other triglycerides that derive from palmitic acid (POP and POS) join in with the crystalline structure of SOS. These triglycerides are a lot shorter than SOS and are often built into the crystal so as to leave gaps. The Chocolate crystal will then readily change to the more stable crystal form “B(IV)” so as to reduce these gaps so producing a different structure and changing the chocolate. This is sometimes known as “fat bloom” and can be clearly seen when cheap chocolate is left for a long time. However it is also known that there are less electrostatic forces holding the B(V) crystals together then in B(IV) so showing that B(IV) is the more stable crystal that Cocoa butter will try to obtain.

Unlike with other food sources such as curries and peppery foods which contain specific molecules which give it its specific flavour, chocolate has no particular molecule to give it its addictive taste. Some may argue that it is the bitter taste of the alkaloid “theobromine” which gives the chocolate its characteristic bitter taste, however it is more likely that the taste and addictive nature of chocolate can be attributed to the amount of glucose present in each bar and the caffeine molecules which are also present.

Developing new and cheaper ways to obtain the perfect structure of cocoa crystals is still needed and the process requires novel ways of forming the B(V) with ease. Of course, with cocoa butter being so expensive it may be more profitable to use research to find a replacement substance or chemical for cocoa butter so as to maximise profits and decrease the amount of farm land needed for cocoa beans. 

“With great beauty comes great danger”- Taking a look into deadly molecules.

I always thought it was interesting knowing that the beautiful and wealthy woman of the past used “belladonna”, poison from the deadly nightshade plant, to make themselves seem more beautiful. Although the psychology behind why wide eyed woman are thought to be more attractive has always been interesting to me, I am most interested in the” whys” and the “hows” and the chemistry behind how their cosmetics actually worked. I have recently been listening to the “Chemistry in its element” a Chemistry World podcast series and whilst doing so I discovered in a short talk by Dan Johnson that the actual molecule behind this attractive pupil dilation is “atropine”.

Atropine looks a bit like this:

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When in the body, Atropine inhibits “Acetylcholine” which is a neurotransmitter at neuromuscular junctions. This disrupts the nervous system and if too much of it enters the body it will inevitably cause death.

In the berries of the deadly Nightshade plant, atropine is found as an “L” isomer; however, the atropine used in medicine uses a racemic mixture of both “L” and “D” isomers. Amazingly, although atropine is very poisonous, like most harmful molecules we have found a way to exploit it for our own benefit!

With Dan Johnson’s story of Atropine, comes the story of an unfortunate lady who was nearly killed by her bitter Gin and Tonic. However, listening to this tail of attempted murder reminded me of a particularly intriguing assignation attempt I read about recently. The assassination of a man named “Markov” was carried out not with Atropine, but another molecule that is found within the deadly nightshade- Ricin. Ricin has caused a great scare in the media over the last century due to lots of failed assassination attempts using letters, however, the most intuitive way I think ricin was used was by umbrella. Markov was murdered after a tiny pellet of ricin was injected into his lower leg by an air gun disguised as an umbrella in a busy London street. Bizar, but deadly!

There is no known antidote for Ricin, and it is such a strong poison that only 7 micrograms is thought to be able to kill a person. Ricin is a molecule that consists of 2 chains. Chain B binds to a particular carbohydrate on the outside of the cell so allowing chain A to eventually enter into the cytoplasm and inhibit the production of enzymes which results in the death of the cell.

Ricin and Atropine are good examples of just two molecules from a deadly plant that have the capacity to cause serious damage, however in the case of both these molecules I find it encouraging to know that although they have the capacity to poison, they also (in some cases) have a capacity to cure, and so save life rather than extinguish it.

(To read more about deadly molecules read John Emsley’s “molecules of murder”).

Fossils and Eumelanin

I was listening to the RSC Oct ’13 chemistry podcast when I first heard Phil Manning talk about the recovery of eumelanin from fossils. This is particularly exciting since fossils were originally thought to be just outlines of what was living- nothing organic was thought to remain; no DNA or proteins, everything of the animal gone. However, the discovery of eumelanin traces on these fossils opens up the opportunity of discovering more about these little known pre-historic creature. Eumelanin and other pigment substances are able to tell us about the colour and pigmentation of the pre-historic being, so opening up a realm of ideas about what they could have looked like.

The good thing about the technique used to discover these traces was that they used “Synchrotron light”. This uses the electromagnetic radiation given out when fast moving (approaching the speed of light) electrons change direction inside a magnetic field which allows us to map the presence of atoms. However it is the non-destructive nature of this technique which makes it so amazing since no material is destroyed or damaged in the process!

To understand more about eumelanin I looked more into the simple “melanin”. Eumelanin is one of 2 classes of melanin: eumelanin (black) and pheomelanin (red). Melanin is a substance formed as part of the process of metabolizing an amino acid called tyrosine and is formed by melanocyte cells in the skin. Albinism is a disease that is associated with the lack of melanin and melanin is often found parts of the brain such as the medulla and zona reticularis of the adrenal gland.

For more on the fascinating research around melanin and eumelanin visit: http://chem.virginia.edu/faculty-research/faculty/john-d-simon/

Silicon deposits and neolithic chefs!

I have always had a love and a passion for food and it has been through chemistry that i have been able to explore in depth the whys and the hows of our food and diet. Last year i was asked to present a speech on how the Romans had affected our lives. Being a passionate eater of course i chose food. The Romans, like the Greeks, to me symbolism the period where civilization was at its greatest, where food and fine dining was really just extravagantly beginning. However This is why I found it surprising to find out about the discovery of the spice “mustard” in early neolithic pots.

The prehistoric periodic has always seemed like a dark age where not much resources were used, and only the basics taken for practical sustenance. However this discovery of 6000 old mustard seems to suggest that humans were using spices to flavor their food so suggesting a style of cooking that wasn’t just a necessity but a pleasure!

An understanding of prehistoric food can be found through the study of “Phytoliths” which are cell deposits formed from the uptake of Si(OH)4 (sillicic acid) from the soil. I find it fascinating that our modern technology is so advanced as to be able to detect these minuscule traces of substances that are found in mustard seeds, especially as mustard is not going to have been kept in large amounts in the first place!

Despite science’s accurate diagnosis of mustard (and in fact garlic mustard!) being used in +6000 year old jars, i am still not convinced that it proves the civilization of the neolithic chefs. I would put forward that it is plausible that such herbs were not used for cooking but for remedies and medicine. In an age where surely everything must have been uncertain and not much understood, I would first think that the mustard may have been thought to have been used for healing and not tasting properties. That said, it is reasonable that strong mustard could equally have been to mask out strong tastes of unpleasant food or even odors!

Take a look at this: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0070583

 

 

A little thought…

I read a particularly interesting article in a magazine the other day about transition metals. Transition metals are a limited source. Well, we say limited, but there are lots of transition metals made on earth they are just deep down in the crust or in extremely inconvenient places. At some point, like oil and fuel, we will run out.

So, what can we do?

Well, demand for transition metals fluctuates, what was considered expensive a century ago is now cheap (i.e aluminium). However, we use them all the time in our increasingly modernising world. There has been talk of collecting transition metals from the sea bed- a process that was considered before but was not commercially viable. Now the need for transition metals is becoming a little more pressed this has started to become a possibility again. However, the solution I quite like the look of is that of gaining them from space!

One possible solution is sending crafts into space to collect transition metals from meteorites. Although this sounds expensive and realistically we should probably try the sea before we go launching our futures and fortunes into the great beyond, I quite like the idea of looking elsewhere. After all we have a universe full of resources; it’s getting to them that is the problem. Mining on meteorites would be fun as most are made strait from the metals that we need- we’d only have to scrape the surface. However it’s the practically 0 gravity that’s the problem. One solution would be to harpoon the meteorite and attach a space mining station to its surface….somehow! (we’ll leave the physicists to work that one out). I like to think of it a little like cowboys and Indians but instead of cowboys lassoing cattle it would be rockets lassoing meteorites….

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Making Ethanedioc acid (or commonly known as oxalic acid)

Oxalic acid is an interesting di-carboxylic acid. This is a molecule that is usually associated with kidney stones, however this painful but interesting molecule, although extremely poisonous, is found in many members of plant species. This includes rhubarb! Rhubarb leaves contain about 0.5% oxalic acid!

Going from CH3C00H to (COOH)2:

To me, this looked pretty impossible–>although these are both compounds found in common food products, it is hard to fathom the steps needed to get from one to the other (Ethanoic acid is sometimes known as “vinegar”). However, the more I looked at this, the more I realised that it actually just takes a combination of 3 well known learnt at AS.

CH3COOH –> CH2CLCOOH –> CH2(OH)COOH –>(COOH)2

The first step is just free radical substitution using UV light and chlorine, the second, a nucleophllic substitution using NaOH (aq) and the third just oxidation with potassium dichromate and H2SO4 under reflux!