Changes in vegetable oil used for commercial frying: A case study from Rawalpindi,Pakistan

The objective of present study was to evaluate the vegetable oils used for commercial frying of chicken and samosa,an indigenous fried product of pakistan. physiochemical analysis of the excessively used vegetable oils showed that refractive index and specific gravity was affected non significantly as a result of frying operation. however,acid value,saponification value,peroxide value,free fatty acids and total polar compounds were significantly lower (p < 0.05) in the oil used before frying as compared to the values recorded after frying operation. the oils,before and after frying of samosa and chicken exhibited the iodine values in the range of 87.9±0.07- 120.5±11 and 86.5±1.03-118.4±10.45,respectively. stearic acid,palmitic acid and oleic acid content were found to be lower in oils before frying than after frying in both the products,however,linoleic acid and linolenic acid indicated higher values in oil before frying than after frying. total polar compounds (tpc) were shown to be significantly lower in oil before frying than after frying of samosa and chicken. tpc increased from 2.3±0.25 to 32.2.9±0.83 and 2.30±0.30 to 29.18±0.96,respectively in oils used for samosa and chicken. the higher values of tpc might be due to excessive number of frying and use of low quality oil. the study concluded that the changes in the chemical profile of excessively used oil were severe enough to cause several health hazards and rendered oils unfit for human consumption.