Effect of convective solar drying on colour, total phenols and radical scavenging activity of olive leaves (<i>Olea europaea</i> L.)

Abstract

Summary In this study, olive leaves, which are known for their therapeutic and antioxidant properties, were used to assess the effect of solar drying conditions (temperature and flow rate) on the drying time and quality parameters of olive leaves. Samples were dried at three drying temperatures (40, 50 and 60 °C) and at two drying air flow rates (1.62 and 3.3 m 3 min −1 ) in a convective laboratory solar dryer. From the experimental results, it was noted that the drying time required to reduce the moisture content to 0.10 kg kg −1 d.b. depends mainly on the drying temperature. The quality attributes of the dehydrated olive leaf samples were investigated in term of colour, total phenols and radical scavenging activity. The effect of solar drying on L*, a* b* parameters was significant ( P &lt; 0.05) for all the studied olive leaves. Besides, the total phenols of olive leaves were significantly ( P &lt; 0.05) influenced by drying air conditions and tended to decrease with increased drying time. The DPPH radical scavenging activity was higher in fresh [EC 50 39.40 (ZR)‐39.95 (CH)] than in dried leaves. However, the radical scavenging activity was also high in leaves dried at 60 °C, 3.3 m 3 min −1 [EC 50 54.21 (ZR)–68.79 (CL)].