The case of cheese puffs vs polyester bags

What do you think is the best part of eating cheese puffs, the crunchy snack or licking your fingers afterward? There’s just something so tantalizing about that neon orange, cheesy powder that keeps you coming back, puff after puff. At least, that’s how it is most of the time, as long as the snack doesn’t stink. That’s right, stinky cheese puffs. What could be worse? This was exactly the problem reported to a client of Polymer Solutions a short while ago, and the materials testing firm was enlisted to investigate the culprit.

I love cheesy poofs, you love cheesy poofs (except when they smell)
In this case, a snack manufacturer was receiving feedback from customers claiming that its cheese puff snacks smelled bad. Naturally, the manufacturer’s first response was to look for a scapegoat, so they tried to pin it on the company that made the bags. The plastics company in question made the bags from polyester, which is a commonly used material in the production of food containers. That’s because polyester, or polyethylene terephthalate makes for an excellent barrier to gases like oxygen and carbon dioxide as well as moisture, according to the Institute of Food Technologies. Polyester is a condensation polymer that is made when carboxylic acid and alcohol react with one another, and it is resistant to heat, mineral oils, solvents and acids, making it perfect for plastic bags.

Polyester on trial
From first glance, it seems like polyester is an unlikely suspect in the mystery of the stinky cheese puffs, but due to the fact that some polyester is the product of recycling, it was worth a look to determine if there was some kind of unknown reaction between the chemicals in the snack and the material that the bag was made of. As far as testing goes, the scientists from Polymer Solutions took a pretty straightforward approach. They first collected two samples of cheese puffs: one from the offending stock of smelly snacks, the other from a normal batch that smelled the way cheese puffs are supposed to smell.

The science behind GC-MS
The team then employed headspace gas chromatography and mass spectrometry to identify the substances that were causing the snack to stink. GC-MS is a procedure that can be employed to identify various gases. They started with gas chromatography to vaporize a sample and analyze the resultant gases. The trick to GC is that different gases take more or less time to move through the separation column to the detector based on their chemical composition. Scientists gain insight regarding the makeup of a gas based on its behavior as it moves through the column to the detector.

Next, they used mass spectrometry, which can identify substances by electrically charging the molecules, accelerating them through a magnetic field, breaking them into charged fragments and detecting the different charges. A spectral plot is then used to display the mass of each fragment. Then, like a puzzle, the technician puts the fragments back together to discover what the original molecule or parent mass was. This is possible because everything has a unique mass spectrum, which means that if you can figure out the mass spectrum of a substance, you can determine what it is.

Off the hook
After applying GC-MS to both samples, the team came to some interesting conclusions. Turns out the polyester bags were falsely accused. Polymer Solutions discovered significantly higher concentrations of volatiles in the odorous sample of cheese puffs, and further analysis determined that they were predominantly hexenal and pentane, both markers of rancidity. That’s right, the cheese puffs were rancid, reaffirming the old adage that “he who smelt it, dealt it.” With polyester’s good reputation upheld, the snack manufacturer was left to figure out what went wrong on their end.