Another of the parameters used to determine the physical changes of the frying oils was the refractive index (RI) (Fig. 2d).According to Abe, Oliveira, Simões, Caldas, and Frazão (2010), RI is related to the fat autoxidation reaction, and its value increases after the formation of peroxides. In oils used in the experiment, changes in RI also depended on the frying duration and the temperature. With increasing frying time, RI increased in all frying media. However,
the highest changes in the refractive index were observed at the highest frying temperatures (180 C). The observed changes are in agreement with the findings from other authors (Khodier, 2002).