Effects of repeated deep frying on refractive index and peroxide value of selected vegetable oils

Abstract

The peroxide values and refractive indices of palm olein, sesame oil and sunflower oil were evaluated before deep frying. The vegetable oils were used to frying white Irish potato chips in three batches, with the peroxide value and the refractive indices of the oils determined after every stage of deep frying. Results of the study show that both refractive index and peroxide value of the vegetable oils largely vary with deep frying. The findings show that refractive index and peroxide value of sesame palm and sunflower do increase on frying, though not in a linear fashion. The refractive index of palm oil increased from 1.4653 to 1.4655 after frying the three consecutive batches; the RI of sunflower oil increased from 1.4722 to 1.4724 respectively. There was no significant change in the refractive index of sesame oil. The peroxide values of palm oil increased from 1.9948mEq/kg to 9.3020mEq/kg after three consecutive deep frying. The value of peroxide of sunflower oil raised from 10.6359 mEq/kg to 19.3101 mEq/kg while that of sesame increased from the initial 3.9914 mEq/kg to 11.9555 mEq/kg on frying the second batch and finally reduced to 11.3095 mEq/kg after frying the third batch of Irish potato chips. Tables 3 and 4 show the relationship between refractive index and peroxide value of the vegetable oil. These findings indicate that repeated deep frying leads to corresponding rancidity and spontaneous deterioration of the vegetable oil.