2.3.6. Total polar materials In the present study, Fri-Check (Fri-Check bvba, Belgium) (Gertz, 2000) was used to measure the degradation of oils in terms of total polar materials (TPM) before and after heating of oil and oil collected after frying of poori. This method is widely followed in food industries and catering restaurants for measuring total polar materials. In this method, oil was filled up to the mark of the cylindrical sensor tube and inserted into the Fri-Check unit. The measurement starts with a beep sound and ends with display of total polar material. The sensor tube monitors the TPM in terms of viscosity changes of degraded frying oils.