Fat Extraction
What is the Soxhlet Method?
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The Soxhlet method is a semi-continuous method to extract fats from a sample. A semi continuous process is one that allows a solvent to build up and surround a sample. The Soxhlet method allows a solvent to run through a sample to extract and collect lipids in a flask. A diagram of the Soxhlet method is shown to the left.
Glassware is set up so that a flask of petroleum ether, sitting on a heating pad, is directly below the thimble with the food sample. As the petroleum ether flask is heated, the liquid will boil and rise up to a condenser tube. Here, the cooling water surrounding the tube will turn the vaporized ether back into liquid. The liquid will drop on top of the thimble with our sample, and soak through towards the bottom, taking along nonpolar lipids with it. As the ether elutes out of the thimble, the liquid ether and accompanying lipids are dropped back into the flask or petroleum ether. This process is allowed to run for 2 hours. At the end of the extraction, the petroleum ether flask will theoretically have all the lipid obtained in a 2 hour time frame. We then dry off the ether with nitrogen and what’s left behind is the measurable lipid. |
Purpose of Experiment:
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To determine the total lipid content of a lasagna sample using the semi-continuous Soxhlet extraction process. Knowing the lipid content in foods is important...click here to find out some of the health effects of dietary lipids.
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Procedure:
With our ground sample of lasagna, we weighed out 1 gram. This sample was packed into a thimble that would be inserted in the soxhlet glassware set-up. After the thimble was placed into the glassware, the ether was allowed to run over the sample. After 2 hours, the flask was exposed to nitrogen, allowing excess ether to evaporate. The lipid that was leftover was observed and measured.
Results:
We observed a color change when we allowed the soxhlet method to run for 2 hours. The lipid leftover was a dark red orange color. The color change is indicative of the lipid soluble dyes that were in our sample. The orange color leads us to confirm the presence of potential carotenes (that normally produce a yellow-red color).
We also measured the mass of the lipid extract. We took known amounts of ground-up sample and for each sample, we found the percent of lipid content. Below is a table of our results:
We also measured the mass of the lipid extract. We took known amounts of ground-up sample and for each sample, we found the percent of lipid content. Below is a table of our results:
We have the percent lipid of about 1 gram of dry sample. We need to now calculate how much lipid is in one serving size of our food sample. We will calculate the fat content as a percentage of the dry weight of one serving size of our sample because the dried sample was used in the experiment. The dry weight of our sample was 58.38g. Below are our calculations:
Discussion/ Improvements:
The fat content given on the food label of the lasagna is 9 grams. We were close, but our value of 7.75 g is less than the value on the label. We would attribute this to the time constraints of the lab. The longer you run the soxhlet process, the more lipid you can extract from your sample. We were able to run the lipid extraction for 2 hours, but if we were able to run it longer, we may have been able to get the ether to extract more lipid and thus give us a more accurate percentage of lipid.