engleski

Involvement of α-, γ-, and δ-Tocopherol isomers from pumpkin (Cucurbita pepo L.) seed oil or oil mixtures in the biphasic DPPH˙ disappearance kinetics

The antioxidant activity of three types of pumpkin seed oil or oil mixtures (cold- -pressed, produced from roasted seed paste and salad) produced in the northern part of Croatia and the kinetics of their behaviour as free radical scavengers were investigated using DPPH. In addition, the involvement of oil tocopherol isomers (α-, γ- and δ-) in different steps of DPPH ̇disappearance and their impact on the rate of reaction were analysed. The kinetics of DPPH ̇ disappearance is a two-step process. In the first step, rapid disappearance of DPPH ̇ occurs during the first 11 min of the reaction, depending on the oil type, followed by a slower decline in the second step. To describe DPPH ̇ disappearance kinetics, six mathematical models (mono- and biphasic) were tested. Our findings showed that γ- and δ-tocopherols affected DPPH ̇ disappearance during the first step, and α-tocopherol in the second step of the reaction. Moreover, α-tocopherol demonstrated 30 times higher antioxidant activity than γ- and δ-tocopherols. The results indicated the bi- phasic double-exponential behaviour of DPPH ̇ disappearance in oil samples, due to the complexity of reactions that involve different tocopherol isomers and proceed through different chemical pathways.

DPPH ̇ disappearance kinetics ; mathematical modelling ; pumpkin seed oil ; tocopherols

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