Hi all,

I keep on reading that chocolate's fats can oxidate when in contact with light... I can't make sense of it. Oxidation is a transformation process due to oxigen (air) so why do they always refer to the oxidation of cocoa's fats by light?

If anyone has a scientific explanation, I am eally interested.

Thanks for your lights.

Olivier

updated by @olivier-l: 04/11/15 04:51:32

Reaction with oxygen is facilitated by light

OliverI asked a similar question in the science of chocolate section and LUV Ice Cream posted a very technical answer. I've been reading up on the degradation of plant fats and it has been very interesting.My question pertained more to heat but I think it would be the same reaction as you are asking about but the heat would just speed up the process.Check it out http://www.thechocolatelife.com/group/nerdzone/forum/topics/chemistry-of-chocolate-seizing-by-heat

THank you Tom and Larry,

Larry, very interesting read However I think oxidation isn't about heating chocolate or that would just be the "fat bloom" problem we encounter with chocolate. Or is it that when people talk about the oxidation of chocolate by light they mean the infrareds heating up chocolate?

I guess I am more looking for a description of what happens in the oxidation process of chocolate by LIGHT.

Thanks to anyone who could have such a description of the process

Oxygen can react with oxygen in two basic ways, either through triplet state or singlet state, usually on the carbon carbon double bonds in fats of protons adjacent these groups. This is why cocoa butter is so stable to oxidation because it does not contain many of these groups. The triplet state reaction is called the ene reaction and the singlet state reaction is a cycloaddition reaction, this is the one catalysed by light because you need light to excite the oxygen to singlet state, this process also requires a sensitiser as well, polyphemols are good at this. I would say most people just throw the term oxidation around and not really understand it. As i said it is not a big problem in chocolate, firstly because the fat is mostly saturated (milk fats on the other hand are different and more susceptible), secondly it is a solid, so only the surface is exposed to oxygen and or light.

photodegredation of proteins and lipids is very common. Most of it's due to UV lights (think fluorescent lighting). Many fats are susceptible to it, the shorter chain and less saturated the fat, the faster it will occur. it's the reason your milk doesn't come in clear containers.

I like the term photo degradation Sebastian, it is more useful for non chemists. Oxidation does not necessarily involve oxygen. Oxidation is just loss of an electon, which photons can do (photooxidation), UV wavelengths as you have pointed out. Other great oxidisers which arent oxygen and dont even involve an oxygen atom are the halogen gases. As you also eluded to different molecules are more susceptible, some like the polyphenols in choc can continue the cascade as well, as once they have lost an electron, and because they are relatively stabilised they can react with other molecules, rather than internal quenching. My question back to Oliver is why the concern, you can delve as deep as you like on this broad and complex topic. Re reading your original question i feel that there is just the confusion in the term photooxidation, which is a process which doesnt have to involve oxygen at all, it is just the removal of an electron from a molecule by a photon and the subequent reaction of the resulting reactive species, usually degradation, as Sebastian said.

Great Tom and Sebastian. THanks to both of you. It makes a lot more sense now and indeed photooxidation or degredation would be a better term. I was just curious to understand how that exposition to light can degrade chocolate. I know what sugar and fat blooms look like and I was wondering what oxidation could do.

you'll taste it far before you see it, but given enough time, the color will lighten. by the time it's noticeably lighter, you don't want to eat it...

Ok I am going to test it . How does it affect the taste?

Thank you

well, if i tell you the results before you test, it can skew your perception 8-) test it and see...