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The present study focuses on the kinetics of degradation of phytochemicals and antioxidant capacity during long-term storage of rapeseed oils prepared from microwave (MV) pre-treated seeds (2–10 min, 800 W). A maximum tocochromanols (90.48 mg/100 g) and phenolic compounds (mainly canolol, 1692.15 μg g−1) concentration is achieved after 10 min of seeds MV pre-treatment, while the highest content of carotenoids (1017.51 μg/100 g) is found in the oils pressed from seeds exposed to microwaves for 6 min. During storage, the tocochromanols and carotenoids decrease following zero-order kinetic, the reduction of phenolic compounds display pseudo first-order kinetic. Storage stability of tocochromanols in the oils obtained from MV pre-treated seeds is comparable to that of the control oil. Oils produced from 8 min MV pre-treated seeds show the slowest progress of carotenoids reduction, as the values of degradation rate constant (k) are lower (14.678 μg/100 g/month) than that of the control oil (18.168 μg/100 g/month). The half-life (t1/2) of oils phenolic compounds increases with longer seeds exposition to MV. Practical Applications: Numerous studies have shown favorable effect of oilseeds thermal pre-processing on the concentration of phytochemicals in the resulting oil. However, there is lack of information regarding storage stability of oils prepared from microwave pre-treated seeds. As the prediction of shelf-life is a desirable goal in the food industry, evaluation of phytochemicals degradation based on the kinetic models will provide information on cost-effectiveness of the seeds thermal pre-treatment prior to oil cold-pressing. The present study focuses on the kinetics of degradation of phytochemicals during long-term storage of rapeseed oils prepared from microwave pre-treated seeds. The study includes a comparative study of kinetics of tocochromanols, carotenoids, and phenolic compounds in correlation with changes in the antioxidant capacity. It is shown that the content of phytochemicals in the oil and their storage stability is significantly affected by the time of seeds microwave pre-treatment prior to pressing.

The purpose of the present study was to extend knowledge concerning the effect of rapeseeds pre-processing methods on the changes in oxidative state, alterations within fatty acids contents and colour of oil. Thermal pre-treatment of non-hulled and hulled rapeseeds by microwave radiation (2-10 min, 800 W, 2450 MHz) was studied in comparison with conventional roasting (20-100 min, 165°C). As rapeseeds were thermally pre-treated, with longer time a significant increase (p < 0.05) in the amounts of total carotenoids, chlorophylls and phenolics in the oils pressed from microwaved and roasted seeds was found. Oils pressed from hulled seeds (HRO) were characterised by significantly lighter yellow hue than non-hulled (NHRO) ones; however, the microwaving and roasting time significantly affected colour change of both types of oils. Although induction period increased with longer seeds microwaving and roasting, oils pressed from thermally pre-treated seeds exhibited higher level of primary and secondary oxidation. Additionally, prolonged seeds heating resulted in unsaturated fatty acids degradation as detected by GC-FID. Based on the results obtained by applying principal component analysis (PCA) it can be concluded that within much shorter rapeseed exposition to microwaves similar compositional changes and degree of oxidation of oils was achieved as during conventional roasting. Practical applications: Colour of edible oil is an important commercial parameter, whereas oxidative stability need to be monitored to ensure high quality of the finished product. Thermal pre-treatment is currently being used in oilseeds pre-processing, but very little researches studied its effect on colour change and oxidative state of oil. Although rapeseed thermal pre-treatment can cause a number of positive quality changes, such as an increase of bioactive compounds, the results should be interpreted with caution since application of too harsh heating conditions may result in unsaturated fatty acids degradation, lipid oxidation or undesirable colour change.