How much saturated fat is in these chips??

Daniel Iversen
R&D Chemist
Lucidity

While eating lunch the other day I was thinking of ways to cut down on my calorie intake and I looked at the potato chips I had packed for the day.  Reading the nutrition label, I saw that total fat and saturated fat was on the label and thought to myself, could the label be that accurate?  I decided to investigate further. 

I wanted to see if I could see a difference between a saturated fat and an unsaturated fat on the Lucidity GC-FID.  From experience I already knew how to make a fat into a Fatty Acid Methyl Ester or FAME, so that is where I started.

I first poured the chips into my 1000 mL beaker and crushed them with a stir-rod until they were fine bits. 

Next, I poured enough PET ether in the beaker to cover the crushed chips and placed the beaker on the hot plate with a stir bar.  The hot plate was set to 60 °C, and I allowed the mixture to heat for about 5 minutes.

After that, I poured the mixture through filter paper and collected the PET ether in a second beaker and set it in the fume hood to evaporate.  After some time had passed, I honestly don’t know the exact time, I got distracted by other things in the lab, probably a meeting or something. I ensured that all moisture and PET ether was removed by gently heating the fat.  

Once I had the fat by itself, I was able to take the mass of the evaporating dish, 79.91 g, and subtract it from the mass of the dish plus fat, 89.95 g.  To my surprise I got 10 grams of fat, the labeled amount on the bag!

Now, I’m not one to want to waste food so I thought, is this procedure accurate enough to get half a gram of fat for the next step without using an entire bag of fat?  I proceeded to do some math, not in my head of course, I had to get out my trusty TI-85 graphing calculator that I used back in my high school days.  The math told me how many grams of potato chips I would need to get exactly 0.5 grams of fat and to my further surprise, not because I don’t believe the method, but because I can’t believe I got the math right on the first try, I got exactly half a gram of fat!

I then proceeded to convert the fats into FAMEs by adding 0.5 grams to an Erlenmeyer flask, followed by 10 mL of Boron trifluoride, then 5 mL of hexane.  This solution was again stirred and heated at 120 °C for 5 minutes.

After the reflux was finished, I removed the flask from the heat and added 10 mL of HPLC grade water.  This solution was then added to a centrifuge tube, and I spun the solution for about 5 minutes in the centrifuge at 5000 rpms.  Once finished I had two distinct layers, the top layer, or for you proper chemists, the supernatant, was removed and diluted with some Isopropyl alcohol.  How much alcohol? Again, I don’t really know, I wasn’t going for an exact amount, just a sort of, will I get a signal from the GC-FID. I figured that was a problem for me in the future.

At the same time, I purchased a FAMEs standard from Restek (p/n35022) to help me identify the peaks.  The standard was run on the Lucidity GC-FID using the following method:

Carrier: Hydrogen

Flow: 2.0 mL/min

Split: 50:1 

Column: MXT-5 (30m x 0.25mm x 0.25um)

Injector Temp: 240C

FID Temp: 250C

Oven Stages:

60C for 2.0 min

10C/min to 200C

Hold for 0.0 min

5C/min to 240C

Hold for 7.0 min 

and all peaks are resolved and match the reference chromatogram provided with the standard.  For further confirmation the standard was run in a GC-MS to confirm the identity of each peak.

The sample was then run in the Lucidity GC-FID using the same method as for the standard, and the resulting peaks were confirmed by GC-MS, which shows the presence of C16:0, C18:2 , and C18:1 methyl ester fatty acids in the sample.

Exporting the result along with the desired parameter of % Area, we are able to see the % Area of each peak, as shown in the table below. 

Peak 1 is C16:0, which is a saturated fat, Peak 2 is C18:2, which is an unsaturated fat, and Peak 3 is C18:1, also an unsaturated fat.  If we approximate the total saturated fat in the sample by using percent area, we can estimate the amount of saturated fat in the fat sample to be around 15.2%, or around 1.5g of saturated fat in 10g of fat, which matches the label!

Not a bad result for a quick and dirty initial investigation of fat in potato chips.  Stay tuned as we delve further into the study.  We’ll be analyzing different types of chips, refining our sample preparation and GC method, and more!