Friday, February 5, 2010

Cooking Oil 101: Chemistry of Acid and Chains

This is a sidebar that never got used for one of my Deli Business articles. My editor gave me permission to publish it here about a year ago, but I never did get around to it. As I'm stuck on a food blog today (and already late), I thought it was a good time to bust it out - especially since it's February and the millions of us may be fussing over our achieved and unachieved weight loss/health goals. Enjoy!

All of the commodity oils start off trans-fat free. However, depending on the types of acids that make up that oil, it may not have a very long shelf life nor be very good for frying up chicken. There are two acids often named in reference to cooking oil: linolenic and oleic.

Before we get into the acids, though, let's take a look at some fat chemistry in general. A fatty acid is made up of mostly a chain of carbon atoms. In a saturated fat, a solid, the carbon chain has two hydrogen atoms attached to each carbon and looks like this:




Linolenic acids are what make polyunsaturated fats. What this means is that the chains of carbon that are the building blocks of the oil have several places where they are double bonded. This kind of bond is not as stable, so it starts to fall apart after time or under high heat conditions. When the double carbon bonds fall apart, they often attract free oxygen atoms, which is what degrades the oil. The more double bonded carbons there are, the easier it is for the oil to degrade. A linolenic acid looks like this:




Oleic acids are what make monounsaturated fats. These fats only have one double bond of carbon. They are much more stable than linolenic acids, but still liquid.




The human body needs and uses both linolenic acids (known as omega-6 for nutrition), and oleic acid (known as omega-9). However, since the linolenic acids are more prone to degradation, they can cause problems in food service with shelf life and smoking point.

Of course, most oils have a combination of many acids, oleic and linolenic among others. For oils that have a higher linolenic acid amount, partial hydrogenation was created. (It is only partial because if it was full, it would create a solid saturated fat.) By creating a chemical reaction and pumping hydrogen into oils, the double carbon bonds are broken, and they grab onto hydrogen atoms (rather than oxygen, which causes the degradation). This makes the oil more stable, but causes other problems. Most simply, it's throwing hydrogen at both linolenic and oleic acids. Second, when the carbon bonds break and grab hold of a hydrogen, the hydrogen can be snagged on either side of the chain. If you look at the linolenic and the oleic acids, you'll notice the missing hydrogen atoms are all on one side. This construction is something the human body can process. The hydrogenation process, however, leaves fatty acid chains with missing hydrogen links on both sides, which the human body has a much harder time processing – so it gets stored in fat cells and on arteries; it's not used as the other types of fat are.

With genetic manipulation, breeding, and more modern processes, oils can be tweaked at seed level to be high-oleic and low-linolenic, which avoids the need for partial hydrogenation. It allows engineers to only address the problem of stability as it relates to the fatty acids. And because research has come so far and these oils are now becoming more available, their price has significantly decreased since the initial attempts to create stable cooking oils without trans fats. Additionally, some of these oils are now performing even better than their partially hydrogenated predecessors, which means the higher price reflects an overall higher value.


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