Wednesday, December 1, 2010

Iodine value: What's that?

A little bit more chemistry for a lovely December morning! 

The iodine value of an oil or butter is a measure of the saturation of the fatty acids. As we go up on the iodine value scale, we'll see more double bonds or more unsaturation in the oils. Something like coconut oil, which has a high degree of saturated fatty acids, will have a lower iodine value (10.4) than grapeseed oil (135), which has a lot of unsaturated fatty acids. For the most part, looking at the iodine value of your oil or butter can give you a lot of information about its shelf life. The lower the iodine value, the longer this oil is likely to last. 

Disclaimer: The iodine value offers very valuable information, but there are some freak oils out there that mess up the whole system. An oil that is very high in anti-oxidants - say, soybean oil (130.5) - will have a longer shelf life than a similar oil that is low in anti-oxidants. Soybean oil has a shelf life of about a year, whereas grapeseed oil has a shelf life of 3 to 6 months. This has to do with the way Vitamin E and other anti-oxidants retard rancity. For the most part, the system works, but there are some exceptions. 

As the iodine value increases, the titer point decreases, meaning the lower the iodine value, the more likely the oil is to be a butter and be more solid. So if I see an iodine value of 15 (babassu oil), I'm fairly sure this is will be solid at room tempearture. An iodine value of 100 leads me to believe it's an oil (like castor or sweet almond oil). 

How do the scienticians determine the iodine value? From Wikipedia: "The iodine value (or "iodine adsorption value" or "iodine number" or "iodine index") in chemistry is the mass of iodine in grams that is consumed by 100 grams of a chemical substance. An iodine solution is yellow/brown in color and any chemical group in the substance that reacts with iodine will make the color disappear at a precise concentration. The amount of iodine solution thus required to keep the solution yellow/brown is a measure of the amount of iodine sensitive reactive groups."

It's all very interesting, but why do we care about this? It's helpful to know the iodine value of your oils so you can determine how long they will live on your shelf and in your products. If you know the iodine value of regular sunflower oil is 132.5, you can predict this will have a short shelf life and add your anti-oxidants or choose another oil. (Noting the exceptions, of course.) 

You can also look at an exotic oil and figure out how thick it might be. If I see a new ingredient - let's call it toasteroven butter - with an iodine value of 36.5, I know it's unlikely to be a liquid and it's more likely to be a butter like cocoa butter (which has an iodine value of 36.5). I also know that it should have a long shelf life. If you see an oil - let's call this one cutiedog oil - with an iodine value of 140, I know this is definitely an oil and likely has a short shelf life. 

If you're looking to add more unsaturated fats in your diet or your products (wonderful fatty acids like oleic or linoleic acid), you can look at the iodine value and determine how saturated it is! 

And finally, it's cool to be able to look at something like an ester and figure out that it's a solid or liquid and its shelf life based on the iodine value (yes, non-natural oils like esters have iodine values as well). So if you see something like cetyl alcohol and see it has an iodine value of 1.0 max, you know it has a long shelf life and is definitely not a liquid! 

So now you know about iodine values! Yay! 

4 comments:

Guy Formulator said...

Thank you for your great post on iodine values.

Not to be a smarty pants, but I think your point about using this value to predict whether an ingredient is a solid or liquid is a little off. It works pretty well for triglycerides, fatty acids, and alcohols, but it breaks down for esters.

For example, isopropyl palmitate has an iodine value of 1.0, the same as cetyl alcohol, and it definitely is not a solid! (freezing point= -3C).

As you rightly point out, iodine value is a good indicator of the degree of unsaturation of the fatty acids and can be a good (but not absolute) indicator of how quickly they will go rancid due to oxidation. Degree of unsaturation also strongly correlates to the melting point (or titer value), but other factors such as the chemical structure can make a big difference.

hasmizaria said...

Hi.
First thank you for the thorough explanation.

I am interested in how this particular property of the oils is beneficial or not for the human body.

My questions are if intake or use externally oils do they actually consume the iodine in the body?

And if they consume the iodine does that new solution of oil-iodine is being released/thrown out of the body, lets say through the urine?

The ultimate questions are, is using oils beneficial for hyperthyroidism and how?

Please let me know if I am not clear in my questions.

Thank you.

Susan Barclay-Nichols said...

Hi hasmizaria. I don't deal with nutrition, so I can't help you.

theDine inDiva said...

Everytime I have an off-the-grid question you have a post about it or relating to it :) Thank you endlessly for the wealth of knowledge you provide! I am AA with non-clumping hair that shrinks ridiculously (when my hair gets wet it tends to shrink significantly into a knotted, tangled mess instead of clumping together into curls/coils or zigzags). I have found what works for hair that clumps is the complete opposite of what works for my hair. I know a lot of things we want to know may not have been explored scientifically but it has been very useful to see what has and has not been explored and the results. I think back to when I was very young I had hair almost to my waist and we used suave and blowdryers along with hot combs and lots of mineral oil a la pink lotion.

I saw on another blog (Ktani's) that the iodine value can be used to figure out how drying an oil/butter is and that the dryness can lead to more buildup and harder removal due to oxygen making the oil more resinous and that the oils polymerize. Is this true? Being that one of my goals is to reduce shrinkage from water uptake this sounds useful!

Off topic but do you know how refining affects an oil? I see info on both sides - refining denatures the oil and reduces/alters beneficial components from the high heat, bleaching, and other refining methods. On other hand (and less easy to find) is advice that refining makes oils safer due to possible contaminants being removed like mold and fungus. Both arguments make sense to me. Aside from avoiding contaminants wouldn't we want to preserve oils and their possible attributes by not excessively heating and refining? I'm not scent sensitive (I can handle straight up neem oil lol) nor do natural colors bother me so I am wondering more for "therapeutic" value (if any) more than aesthetic desires. This applies more to skin than hair I guess since hair is dead and only benefits from certain substances. Cheers!