Influence of the preparation method on the bioactive compounds of olive tree leaf tea

Abstract The general objective of the research was to investigate whether the preparation methods interfere with the polyphenols availability and the antioxidant capacity of olive leaf teas prepared from dry leaves. Leaves of the cultivar Arbequina were dried in an oven with air circulation and renewal at 40 °C/48 hours. The teas were prepared with 7% dry leaves through infusion and boiling for 10 minutes of process. Part of the liquid teas were freeze-dried. The samples of liquid tea and freeze-dried teas were evaluated for: total phenolic compounds (TPC) (using the Folin-Ciocalteu reagent), polyphenol profile (High Performance Liquid Chromatography - HPLC), and antioxidant capacity by the ABTS assay. It was observed that the boiling method released more polyphenols than the infusion and a greater antioxidant capacity in liquid tea and freeze-dried tea. Oleuropein concentration was favored by the boiling method regardless of whether the tea was freeze-dried or not. Although boiled tea presented a higher total polyphenol content, there was a reduction in the flavonoid levels. Additionally, freeze-dried tea prepared by infusion also showed the highest levels of flavonoids and phenolic acids. In conclusion, the consumption of dehydrated olive leaf tea prepared by boiling offers higher levels of polyphenols and antioxidant capacity than tea prepared by infusion.