Influence of freezing and dehydration of olive leaves (var. Serrana) on extract composition and antioxidant potential

In this work, the effect of the methods used for the freezing and drying of olive leaves on the polyphenol content and antioxidant capacity of the extracts was addressed. Thus, different methods were used to dry olive leaves (fresh or frozen by conventional (-28 degrees C) or N-2 freezing): hot air drying at 70 or 120 degrees C and freeze drying. The extracts were characterized by determining the phenolic content, antioxidant capacity and HPLC-DAD/MS-MS profile. Drying had a significant (p<0.05) influence on the antioxidant potential of olive leaf extracts. Both the drying and freezing methods significantly (p<0.05) influenced the concentration of the main polyphenols identified. Hot air drying provided a higher phenolic content, especially in oleuropein, than freeze drying. Thus, drying at 120 degrees C was the best processing condition. Freezing reduced the antioxidant potential as compared to fresh leaves, probably due to oxidase activation, although its influence was not dependent on the freezing method. (c) 2012 Elsevier Ltd. All rights reserved.