The effects of temperature changes on the kinetic parameters of sesame, canola and olive oils in the presence of sesamol

Lipid oxidation is one of the most important factors affecting the loss of quality or the deterioration of edible oils. This reaction is accompanied by the production of harmful compounds that may threaten consumer’s health. Several parameters affect the severity of the oxidation reaction, among them temperature is one of the most important parameter to consider.  Lipid oxidation increase significantly with the increase of temperature, which drastically reduces the length of the shelf life of the oils. Numerous methods have been used to postpone the oxidation of oils that one of the most useful methods is the addition of antioxidants. Nowadays, natural antioxidants have been located in the hotspot of attention from safety and sensory characteristics point of view. Sesamol as a valuable natural antioxidant may help to provide healthy edible oils. The determination of thermal kinetic data and the evaluation of thermodynamic indices have long been used to the better identify the mechanisms and the events caused by temperature elevation. Examining the temperature and time variables together and merging these components could provide valuable information about the environmental effects of foodstuffs. These parameters are particularly important for edible oils. Hence, the kinetic-thermal information of the oils oxidation in the presence of sesamol may provide the valuable assistance in explaining the storage conditions of various edible oils in the presence of this antioxidant.

The sesamol's ability to quench free radicals was determined by DPPH test and at 517 nm. The oil purification process was performed by adsorption column chromatography in order to eliminate minor components that may be interfere with the oxidation reaction. The evaluation of the accelerated oxidation process in presence of sesamol was carried out in a dry oven and through monitoring the accumulation of hydroperoxides (peroxide value) over time at 60, 80 and 100 °C. The peroxide value was measured spectrophotometrically at 500 nm. The induction period of oils oxidation was determined through two lines fitted on initiation and propagation steps of the oxidation curve. The rate constants of the oils oxidation and sesamol consumption, the peroxide value corresponding to the length of induction period (PVIP), the minimum sesamol concentration to demonstrate the antioxidant activity and the oxidative stability time of lipid systems at ambient temperature were also determined by oxidation kinetic data.

The results of inhibitory test showed that the amount of sesamol required to inhibit 50 percent of the DPPH radicals is equal to 1 mM. The induction period of olive oil has reached to over 520 h in presence of 0.01% sesamol at 60 °C, whereas sesame and canola oils were placed in the subsequent positions with nearly 330 and 325 h, respectively. The average extent of PVIP (all sesamol concentrations) for two lipid systems i.e. sesame and canola oils was close to each other and drastically higher from olive oil. This delocalization of the numbers suggests that the PVIP is independent of the antioxidant concentration available and is affected by the fatty acids structure of oils. The effect of temperature elevation on the rate constant of oxidation for different oils did not follow the same pattern, so that the slope of increase of the rate constant for olive oil was very mild than to the other two oils. The results showed that the increase in temperature has markedly increased the rate of sesamol consumption, so that unsaturated lipid systems have undergone significant changes in this regard. Increasing the temperature increased the minimum concentration required for the antioxidant activity of sesamol. This pattern was linear for olive oil and hyperbolic for sesame and canola oils.