When I got back from Columbus last Monday morning I worked almost 10hrs and was busy revising power points and final papers for my 2x REU students (Research Experience for Undergrads) who finished their 10wk appointment this past friday.
Both were rising sophomore undergrads, one at The University of Delaware and one from NC State. They were posted in my lab for the summer under the C2B2 program (biofuels/biorefining research) and although I was only originally supposed to get one of them, I was lucky enough to end up mentoring both which, though hectic at times, was really a blessing because we got lots of high quality data and I was able to teach them a bit about science. Unfortunately, now they are gone and the lab is back to normal (and now I am going to have to actually do things again). Here is a little tour:
One of the projects that I am currently working on is the selective hydrogenation of fatty acids. For those that arent familiar, fatty acids are the components of plant oils; everything from sunflower, olive, walnut, vegetable, coconut, rapeseed, canola, peanut, palm, sunflower, sesame, and the list goes on and on. What each of these have in common is a fatty acid head group followed by a hydrocarbon tail. The differences are in the length of the tail, and the number, type, and place of double bonds in the tail. For example, here is cis-9-octadecenoic acid commonly known as "oleic acid" which makes up 70% of olive oil!
These oils are useful as fuels because they have that nice long hydrocarbon tail! We just want to do things that remove the fatty acid (on the right) to make the molecule less viscous. One way to make it less viscous without taking off the fatty acid is to make biodiesel. This is done by transesterifying the fatty acid head so the molecule is more volatile (and less slimy-ish). Another way would be to cut off the fatty acid completely, but this is far more difficult and energy intensive.
Besides fuels, we also like plant oils for foods because they provide us with a lot of energy compared to other food sources:
Oils/fats: ~9kcal/g
Alcohol: ~7kcal/g
Carbs &protein: ~4kcal/g
Of course there are bad fats as well. In the picture of oleic acid above, you can see a big kink in the middle which prevents a large group of these molecules from laying flat on top of each other. This is a "monounsaturated fat" because it has 1 double bond. If it had two or more double bonds (and was even more kinked) it would be a "polyunsaturated fat." If that double bond weren't there (indicated by the = sign), the tail would be straight, the molecule would be a "saturated fat," and would stack on top of its friends (and in your arteries). Saturated fats are also bad for fuels--can you imagine putting butter in your gas tank?
A small portion of my research delves into the issues associated with the degree of saturation, but the interesting things that I wanted to post here are my FUN SCIENCE EXPERIMENTS!!!
EXPERIMENT #1
Since I already do fatty acid analysis in lab, I decided to bring in samples of vegetable oil, olive oil, coconut oil, and walnut oil from home and analyze their compositions. First of all, everything I measured was measured as a free fatty acid, meaning that it is free of a triglyceride structure. So you can see below, a triglyceride is three fatty acids connected to a glycerol molecule. When the fatty acids come off they are "free!" Just like the pictures above of oleic acid, that's what we eat and that's what I analyzed (not this big klunky thing below).
Since these oils contain a mixture of molecules, I use a notation of the number of carbons followed by their unsaturation. So, C18:1 means that it is an 18 carbon tail with 1 double bond. In fact, C18:1 is what oleic acid would fall under! Here is what I found:
| Other | C12:0 | C14:0 | C16:0 | C18:0 | C18:1 | C18:2 | C18:3 | |
| Olive Oil | 2% | 0% | 0% | 13% | 1% | 72% | 11% | 1% |
| Vegetable Oil | 2% | 0% | 0% | 6% | 1% | 64% | 18% | 9% |
| Walnut Oil | 0% | 0% | 0% | 10% | 4% | 28% | 52% | 6% |
| Coconut Oil | 8% | 49% | 23% | 11% | 4% | 4% | 1% | 0% |
To no surprise, olive oil contained a whole lot of C18:1 indicating a large presence of oleic acid. Vegetable oil and walnut oil were more unsaturated (there was more C18:2 and C18:3 present). Coconut oil was the weirdest of the bunch showing a wide range of short saturated 10-16 carbon chains. Because they are shorter, they are more likely to stay liquid but if you have any at home, you know that coconut oil melts at about 75F (so in our house it is rock hard in the winter and liquid in the summer). Coconut oil is also "good for cooking" because it has no double bonds to react. But is olive oil really "bad for cooking?"
EXPERRIMENT #2
I have heard that cooking with olive oil is dangerous because it can isomerize under heat and form trans fats. As I mentioned earlier, oleic acid is good because it is bent, but the same formula can shift to a straight structure (the trans version) which is bad for your health sort of like a saturated fat, as you can see below.
So, I took home 8 sample vials and put a half cup of olive oil in a frying pan. I heated the oil to its smoke point (200C) and took samples for 20min. I estimated that this was a reasonable cooking time even if 200C was rather hot. By the end, our house was pretty much smoked out and the only qualitative change I noticed was that over time, the oil had become less viscous (duh) but also lighter in color.
To my surprise, when I analyzed these samples, there was no change in the composition! In fact, I measured to an uncertainty of < 0.5% and was unable to detect any trans fatty acids! I checked some literature here at work, and as it turns out, there are a number of other scientific studies that did the same tests as me (well they were a little more scientific) but they found the same thing--no change in composition.
I guess the moral of the story is that oleic acid really is the nectar of the gods. You can cook with it, eat it plain, put a little bit in your hair when youve had a rough week--what do you think holds it up, slick? I could be biased but I go through about a liter a month of the stuff. Still I am losing to the greeks who consume on average 23.7 kg per person per year!
Rudy
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