Rancidity of Tortilla Chips Leads to Outbreak of Gastrointestinal Distress

Approximately 77 people became ill in a correctional facility in Wyoming after eating rancid tortilla chips.  Rancidity is the breakdown of oils and fats that occurs when fats and oils were extensively heated.  Debris and moisture in the oil facilitates that breakdown.  This oil breakdown impacts flavor and quality, and as seen here, can lead to gastrointestinal distress.   In this case, the tortilla chips were probably fried in oil that had been used too long.

Generally indicators of rancidity are measured to detect the level of rancidity, in this case, hexanal and peroxide.  By measuring these indicators, firms know when oil is beginning to go bad and then replace the oil.  For smaller firms without the capability of conducting measurements, they replace oil after a certain time or amount of usage.  Others replace oil when the oil in the fryer begins to darken, smoke or smell 'off'.  Continuing to use oil after it goes rancid leads to off-flavors in the food, and more importantly, illness.

As noted in the MMRW article, this is one of the first documented cases of illnesses related to rancid oil.  But a good guess would be that this happens more frequently than reported.  How many times have you gone to a fair or a greasy spoon burger joint and ate fried food that had an off-flavor?  Then a hour or two later your stomach starts to roll.  Too often, purveyors try to use oil longer than it should be used.  In some cases, the consumer notices the flavor and throws the food out, but in other cases, when really hungry, they choke it back.

Morbidity and Mortality Weekly Report (MMWR)
https://www.cdc.gov/mmwr/volumes/65/wr/mm6542a4.htm?s_cid=mm6542a4_w
Gastrointestinal Illness Associated with Rancid Tortilla Chips at a Correctional Facility — Wyoming, 2015
Weekly / October 28, 2016 / 65(42);1170–1173
Tiffany Lupcho, MPH1; Alexia Harrist, MD, PhD1,2; Clay Van Houten, MS1

 Summary

What is already known about this topic?
Although consumption of rancid food can cause gastrointestinal illness, few outbreaks have been documented.