The effects of conventional heating on phenolic compounds and antioxidant activities of olive leaves

Phenolic compounds, antioxidant activities and total phenolic contents of leaves from different olive varieties (Gemlik, Kalamata, Yağlık and Sarıulak) were evaluated after conventional drying at different temperatures (50, 60, 70 and 80 °C). The drying process resulted in non-significant effects on olive leaves. The phenolic contents however, varied with drying temperature. The contents of minor total phenolics in Gemlik, Kalamata and Sarıulak leaves were 1457.6, 1899.3 and 2179.8 mg GAE/100 g, respectively when dried at 60 °C. The highest total phenolic reduction (23.2%) was observed in Kalamata leaves after drying at 80 °C. The major phenolic compounds in olive leaves were gallic acid (101.2–439.7 mg/100 g), 3,4-dihydroxybenzoic acid (66.7–460.4 mg/100 g), (+)-catechin (39.2–667.8 mg/100 g), 1,2-dihydroxybenzene (15.8–584.8 mg/100 g) and quercetin (33.1–277.7 mg/100 g). It was observed that olive leaves from different varieties are rich in phenolic compounds which are sensitive to heat and varied with drying temperature.