Transformations and antioxidative activities of lignans and stilbenes at high temperatures

• Phythochemical phenols of the lignan and stilbene families showed good stability at elevated temperatures. • Lignans and stilbenes retained their antioxidative properties even at temperatures up to 200 ˚C. • The studied phenols showed to protect the PUFA linoleic acid against high temperature degradation and significantly decreased the degradation rate. Thermal transformations of polyphenols from the lignan and stilbene families were investigated at temperatures ranging from 200 ˚C to 250 ˚C, in polyethylene glycol (PEG-400), dimethylformamide (DMF) and in sunflower oil (SO). The polyphenols showed varying degrees of thermal stabilities and in some cases intramolecular transformations were observed. The formed products were isolated and characterized. Oligomerization of the polyphenols at thermo-oxidative conditions was also investigated. Finally, the antioxidative activity of the polyphenols against thermo-oxidative degradation α -linoleic acid was investigated at 200 ℃. The results suggested that the studied substrates retained their antioxidative properties at elevated temperatures, with stilbenes showing most efficient protection against thermo-oxidative degradation of polyunsaturated fatty acids.