Thermal Degradation and Safety of Repeatedly Heated Palm Kernel Oil During Deep Frying

Abstract

There is limited research on the safety of repeatedly heated palm kernel oil for deep frying of various food commodities. This study, therefore, investigated the safety of palm kernel oil at different frying cycles by examining the changes in moisture content, color, free fatty acids, peroxide value, and saponification value using standard methods. The results indicated a significant upsurge (p < 0.05) in free fatty acids (FFA), peroxide value (PV), and saponification value (SV), with a strong positive correlation among the three parameters after repeated frying. However, a negative correlation was observed between moisture and the oxidized metabolites (FFA, PV, and SV) when subjected to multivariate analysis (principal component analysis). Because the quality of the palm kernel oil deteriorates beyond the acceptable safe limit (15 meq/kg for peroxide value) at the third frying cycle, it is recommended that palm kernel oil should not be reused after the second frying cycle.