Probe detects cooking oil gone bad

Most people who eat in restaurants probably don’t think about how often the staff changes the oil in which the food is cooked. But what patrons don’t know can still make them sick. Fortunately, researchers have developed a fluorescent probe that could help keep consumers safe by identifying even small amounts oil gone bad.

Lipid oxidation occurs when cooking oils are reused too many times, causing chemical processes that lead to changes in flavor, aroma, and nutritional quality. The large amount of isolated trans-fatty acids found in bad cooking oil has been linked to arteriosclerosis and heart disease.

Researchers developed a fluorescence sensor that identifies when used cooking oil should be discarded and replaced. Courtesy of iStock.com/Everyday better to do everything you love.

“If it is cooked oil, over time, [the] reactive oxygen species (ROS) generated would be the main source of health problems,” said Young-Tae Chang, a chemistry professor at the Pohang University of Science and Technology (POSTECH). “The radicals [unstable metabolites of oxygen], especially, are hydrophobic as part of oily material, and their residence and persistence in the body make an even higher impact than soluble ROS.”

Researchers from POSTECH, the Institute for Basic Science, the National University of Singapore, and Daegu Gyeongbuk Institute of Science and Technology developed the sensitive molecular probe that fluoresces in the presence of the harmful chemicals generated by bad cooking oil. Conventional methods for detecting this health hazard measure only the acidity of cooking oils, and the technologies are not easily accessible to the public.

So, the research team cooked up their own solution using a dual turn-on method to detect both viscosity and acidity in oil using a portable platform called the Bad Oil Sensing System (BOSS). The system is designed to be used by consumers as well as professionals in the food industry.

Chang said BOSS was used to test the fluorescence present in oil after 12 hours of heating, but a signal could be found after even one hour.

Other technologies that are employed to identify changes in the properties of cooking oils and other products include chromatography, mass cytometry, nuclear magnetic resonance, Fourier transform infrared spectroscopy, Raman spectroscopy, and atomic absorption spectroscopy. However, these methods require the use of expensive equipment and skilled professionals, the researchers said.

The researchers’ approach uses the inherent fluorescence of the compounds, as well as the elevated pH levels found in heated oil, and isolates them using BOSS, which contains a light source and separate filter, detection, and signal display modules. Each sensor has an optimal excitation in the green wavelength at around 535 nm. Different varieties of cooking oils were used to provide a more robust experiment. The system would need to be upgraded before large-scale production of the platform and broad commercialization of the method would be possible, Chang said.

“Domestic users, regulators, or a franchise company may need a handy oil checker, and the Bad Oil Sensing System could be a good option for them,” he said. The test requires just a drop of oil for a sample, and the researchers used a well plate for each test.

They found that the probe detected even a small amount of bad oil mixed in with fresh oil. Chang said the signal increase created by the bad oil is about tenfold, meaning that if the percentage of bad oil is 10%, it would still be very visible in measurements.

So both eateries and patrons could be assured that not only have fresh ingredients been used in the meals on the table but also that the oil in which the ingredients were prepared was fresh.