Thermostability and degradation kinetics of tocochromanols and carotenoids in palm oil, canola oil and their blends during deep-fat frying

•The phytonutrients' deterioration reaction orders were greater than one.•The composition of the oil samples affected the phytonutrients' thermo-stability.•The tocopherols and tocotrienols was most stable in the blend oil samples.•The carotenoids were most retained in the virgin palm oil after frying.•The least stable homologs in the oil samples were γ-tocotrienol and γ-tocopherol.

The thermostability of tocochromanols (tocopherols and tocotrienols) and carotenoids in virgin palm oil (VPO), refined canola oil (RCO) and blends of the two oils under deep-fat frying conditions at 170-190 °C was investigated. Normal-phase HPLC was used to monitor the tocochromanols variation over frying time at each temperature. The changes in total carotenoids content was analyzed spectrophotometrically. The deterioration kinetic rate of each homolog detected followed a reaction order greater than 1. The rates were dependent on frying temperatures and were satisfactorily modeled by the Arrhenius relationship. The rate of deterioration and the activation energy showed that the least stable homologs were γ-tocopherol and γ-tocotrienol while δ-tocotrienol and carotenoids were the most stable. In VPO, the carotenoids were more retained while the tocochromanols were less stable. This was further evidenced by the high activation energy (Ea of 71 ± 5 kJ/mol) for carotenoids in VPO. The tocopherol and tocotrienol homologs had greater stability in the blends as shown by their comparatively higher Ea values. The Ea for γ-tocopherol, γ-tocotrienol, α-tocopherol and α-tocotrienol in the blend were 20 ± 2, 47 ± 16, 48 ± 9, and 74 ± 4 kJ/mol, respectively. These behaviors are related to the initial composition of the oils and their calculated oxidizability (Cox) value.