The intersection of food and fuel chemistry – #foodchem carnival

CENtral science are hosting a blog carnival from November 11-18 about food chemistry, #foodchem. As a non-US chemist, the Thanksgiving theme of the #foodchem carnival is not all that relevant to me, so I haven’t followed the questions and am instead writing about something which I find interesting – an intersecting area of food and fuel chemistry.

At first glance, it might appear that foods and fuels could be almost as far apart as you can get in the world of applied chemistry, but as this Harris cartoon (third one down, right hand column) suggests, there are actually some interesting parallels.

Several years ago, I worked for a government organisation where I completed a significant project assessing the levels of trans fats in a range of supermarket foods. The fat content of the foods was profiled, down to the amounts and types of fats present (saturated, mono-, poly-unsaturated, and of the unsaturates, cis and trans isomers). This also allowed the checking of whether the labelling was correct, in the cases where fat levels were reported by the manufacturer either voluntarily or as required.

In order to determine the amounts and types of fats present, it must first be extracted, or separated from the rest of the ingredients in the food. Often, especially with porous foodstuffs like cakes, breads and biscuits, the fat can be easily recovered from the food by simply mixing with hexane or heptane, which easily dissolve fats. More difficult matrices such as chocolate, emulsified sauces and tinned meats required more exhaustive and technical extraction procedures.

The fat is isolated from the food still chemically intact, in the form of a triglyceride (see below). As the name suggests, it consists of a trio of fatty acids (in blue), linked together by glycerol (in pink). In this example, all of the fatty acids in the triglyceride are the same, but this doesn’t have to be the case. There can be a mixture of lengths, and varying degrees of saturation. For this reason, it is necessary to break apart the triglyceride into the separate fatty acids for analysis. This is done by performing a very simple chemical reaction called transesterification, and here is the where the link with fuels is revealed. Transesterification of oils and fats is the exact same reaction that is used to produce ‘biodiesel’, which is also known as FAME (fatty acid methyl esters) or ‘first generation alternate fuel’ within the fuel industry.

Image

It is clear that biodiesel can be easily made from fats and oils sourced from virtually anywhere, and for commercial production, ideally these should be non-food sources. Backyard biodiesel production is also not uncommon, and for many people with a connection to a restaurant or café producing waste oil, can be a cheap and sustainable way to run a forgiving, diesel-fuelled vehicle. This of course, should only be done with the correct equipment, PPE and sufficient knowledge to carry out the procedure safely.

In my lab, we have produced some small quantities of biodiesel from high fat foods, as part of an undergraduate student project and also a science outreach opportunity as we use the samples in our lab tours.

% total fat by weight Amount biodiesel produced
1×McDonalds double quarter pounder burger 17 ~50 mL
1×McDonalds large fries 19 ~25 mL
12×Krispy Kreme doughnuts 25 ~100 mL
1 pack (13) Scotch finger biscuits 21 ~20 mL

As you can see, this is far from an economical or efficient way to produce fuel (a dozen doughnuts wouldn’t even get you a kilometre down the road), but it is a great experiment for students to do to develop their wet chemistry techniques, and also think about the structures of common molecules. So next time you indulge in some fatty food, think about how with a quick chemical reaction you could convert your human fuel into fuel for your car or truck. Nifty!

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