Drying and storage of olive leaf extracts. Influence on polyphenols stability

• Impact of drying and storage on olive leaf polyphenols has been studied.
• Drying of leaves determined the bioactive content of extracts during storage.
• Extracts dehydration only meant a reduction in antioxidant potential of around 10%.
• Extract form (liquid or powder) and storage temperature did not affect phenolic content.

There is an increasing demand for natural antioxidants in the food, cosmetics and pharmaceutical industries which has led to the search not only for natural extracts but also for strategies with which to increase long-term storage stability. The aim of this work was to assess the influence of the drying and storage of olive leaf extracts on the bioactive potential and stability of polyphenols. Olive leaves were hot air dried (120 °C) and freeze dried. Then the extracts were obtained by maceration (ethanol–water, 80:20, v/v). Afterwards, a part of the extracts was hot air dried at 120 °C and vacuum dehydrated at 55 °C. Thus, the extracts, in liquid and powder forms, were stored at 4, 25 and 35 °C for 4 weeks. During this period, the extracts were characterized by determining the antioxidant capacity (AC), the total phenolic content (TPC) and the concentration of the major phenolic compounds.The experimental results highlighted that drying the raw material not only influenced the initial extract composition but also the bioactive potential evolution during storage. Regardless of the method used, extract dehydration reduced both the AC and TPC by around 10%. Finally, storage conditions (temperature and extract form) did not have a significant (p < 0.05) effect on the extracts’ antioxidant potential.