The study, published in the Journal of Agricultural and Food Chemistry investigated the quality, stability and fatty acid composition of a range of frying oils – including refined olive, corn, soybean, and sunflower oils - in successive deep-frying sessions.
Led by Mohamed Bouaziz from the Université de Sfax in Tunisia, the international research team noted that different oils have a range of physical, chemical and nutritional properties that can degrade oil quality when heated or repeatedly used. Some of these changes can lead to the formation of new compounds that are potentially toxic, noted the team, while by-products of heating oil can also lower the nutritional value of the food being fried.
After assessing which cooking oil can maintain its quality under high heat and repeated use, Bouaziz and his colleagues reported that
“Changes in the characteristics and compositions of the studied oils have shown that refined olive oil is the most stable oil during deep-frying at 160 °C, whereas refined sunflower oil is the least stable during pan-frying at 180 °C,” wrote the researchers.
“Therefore, refined olive oil appears to be a good substitute for the refined seed oils.”
Bouaziz and his colleagues deep- and pan-fried raw potato pieces in four different refined oils — olive, corn, soybean and sunflower — and reused the oil ten times.
Several chemical parameters - including free acidity, peroxide value, total phenols and total polar compounds (TPC) - were assayed during frying operations to evaluate the status of the frying oils.
“Today, it is well-known that when its TPC percentage is more than 25%, a fat or an oil for frying purposes must be discarded,” said the team.
The tests revealed that refined olive oil, as frying oil, was more stable than the refined seed oils.
“In fact, this oil has proven the greatest resistance to oxidative deterioration, and its trans-fatty acid contents and percentages of total polar compounds were found to be lower at 160 °C during deep-frying,” reported Bouaziz and his team.
In addition, they noted that chemometric analysis showed that the lowest deterioration of the quality of all refined oils occurred in the refined olive oil during deep-frying at 160 °C and that the highest deterioration occurred in the refined sunflower oil during pan-frying at 180 °C.
Source: Journal of Agricultural and Food Chemistry
Volume 62, Issue 42, Pages 10357–10367, doi: 10.1021/jf503146f
“Monitoring of Quality and Stability Characteristics and Fatty Acid Compositions of Refined Olive and Seed Oils during Repeated Pan- and Deep-Frying Using GC, FT-NIRS, and Chemometrics”
Authors: Akram Zribi, Hazem Jabeur, et al