The extreme conditions during deep frying result in a number of chemical reactions that deeply affect the quality of the frying products, including oxidation and polymerization of unsaturated fatty acids. Resistance to oxidation during frying depends on the fatty-acid composition and on the presence of antioxidants. Thus, the antioxidants present in the oil, either naturally or added from different sources, have a hugh impact on the quality of the oil during the frying process.

Bertrand Matthäus, Max Rubner Institute, Detmold, Germany, and colleagues investigated the impact of lipophilic components from three different herbs: sage, thyme, and rosemary. These lipophilic components were extracted by stirring the herbs for 24 h at 30 °C in rapeseed oil. This flavored oil is more stable in the Rancimat test at 120 °C, but less stable during deep frying compared to the control. However, despite the significantly higher level of thermooxidative degradation, in the flavored oil prepared French fries remained acceptable, whereas those fries prepared in the control oil were judged as unacceptable.

Further research is still required to understand the contributions of extracted components to the thermooxidative stability of the oil.

• Stabilization of refined rapeseed oil during deep-fat frying by selected herbs,
  Eman Taha, Salah Abouelhawa, Mohamed El-Geddawy, Mohamed Sorour, Felix Aladedunye, Bertrand Matthäus,
  Eur. J. Lipid Sci. Technol. 2014.
  DOI: 10.1002/ejlt.201300279