Obtaining sugars and natural antioxidants from olive leaves by steam-explosion

In this work, steam-explosion treatment was evaluated as a procedure to recover sugars and natural antioxidants from olive tree leaves. The treatment was carried out following a Box-Behnken experimental design, with three factors, temperature (180-220 °C), process time (2-10 min) and milling time (0-15 s). Response surface methodology showed that temperature was the most influential factor, followed by process time, while the best results were achieved with whole leaves. The operational conditions for simultaneously maximizing the sugars and natural antioxidants recoveries resulted to be 180 °C, 8.3 min and whole leaf; under these conditions 18.39 g and 1950 mg were obtained from 100 g dry olive leaves, respectively. This is equivalent to 70% recovery of the initial sugars present in olive leaves, with a very low formation of inhibitory compounds and an important amount of natural products with antioxidant capacity such as oleuropein, hydroxytyrosol and flavonoids.