The effect of drying on phenolic compound, antioxidant activity, and mineral contents of leaves of different olive varieties

The highest total phenol contents were found in olive leaves heated in microwave 540 W and athmospheric air. While the antioxidant activity of olive leaves heated in microwave 180 W change between 76.99% (Akdeniz Yerli) and 82.26% (Sarı Ulak), antioxidant activity values of leave samples heated in microwave 360 W varied between 81.20% (Yağlık) and 82.24% (Gemlik). The highest p-coumaric acid (161.92 mgGAE/100g) and trans-ferulic acid (3,276.09 mg GAE/100g) were determined in Akdeniz yerli olive leaves dried in microwave 360 W. In addition, the highest oleuropein content (1,104.66 mg GAE/100g) was found in Akdeniz yerli olive leaves in control group. The Ca contents of olive leaves dried in microwave 540 W vary between 12,300.34 mg/kg (Akdeniz Yerli) and 16,437.52 mg/kg (Sarı ulak), Ca contents of olive leaves dried in oven (70 °C) were changed between 10,188.19 mg/kg (Akdeniz yerli) and 16,801.42 mg/kg (Sarı ulak) (p <.05). Practical application: Olive oil is important for economic value. But, recently olive leaves were used as a medicinal plant in an infusion or decoction forms. Because, oleuropein is a phenolic compound of olive leave and its useful for human health. The best known oleuropein source is olive leaf. Drying process was affected on change of chemical and bioactive properties of plant materials. The drying process is important not only for the preservation of vegetable materials but also for the preservation of the nutritional value and the functional properties without deterioration.