Olive leaves infuse and decoct production: Influence of leaves drying conditions and particle size

Taggiasca, a cultivar grown typically in western Liguria (Italy) and in the southern regions of France, is a tasty and sweet olive for table consumption and for the oil production. Olive oil production generates a huge amount a wastes. Besides the traditional olive mill wastewater and olive pomace, leaves of the trees are considered by-products and nowadays they are burned or used as animal feeds despite they have high content of bioactive compounds. Oleuropein, apigenin and vanillic acid are examples of polyphenols contained in olive leaves and their content changes depending on the cultivar, the region of growth and the harvesting time. The aim of this work is to valorise one of the by-products of the olive oil industry. The study aims to investigate the effect of the pre-treatment processes on the production of olive leaves infusion. Different drying techniques and particles size have been evaluated in order to produce an extract rich in phenolic compounds. Olive leaves (Taggiasca cultivar) were kindly provided by the Azienda Agricola Castellari company, Savona, Italy. Leaves were collected and immediately washed and dried at different temperatures (50, 60 and 70 \ub0C) in a ventilated oven. Moreover, an additional drying at 70 \ub0C was performed under nitrogen atmosphere. In order to evaluate the effect of the drying temperatures on total polyphenol (TP) and flavonoid (TF) yields and on antiradical power (ARP) of the extracts, samples were grinded (0.8-0.59 mm) using a laboratory mixer. Powders were then extracted using ethanol and analysed. Based on those results, the best drying condition was used to evaluate the influence of the matrix particle size on the extraction yield after ethanol extraction and teas production. Sieves (4, 9, 16, 20 and 30 Mesh) were used to obtain powder with particles distributed uniformly in the range 2.19 < A < 4.76, 1.19 < B < 2.19, 0.84 < C < 1.19 and 0.59 < D < 0.84 mm. Olive leaves teas were prepared as follow: 1) infusion, 200 ml of deionised boiling water were added to 2 g olive leaves powder and let them soak for 3 min without additional heating; 2) decoction, 200 ml cold water were added to 2 g of olive leaves powder and boiled for 15 min, waiting for 10 min after boiling before carrying on the analysis. After extracting with ethanol the dried matrix obtained at different temperatures, we found out that there was not statistical difference (p<0.05) in the TP (25.06\ub11.00 mgGAE/gDL) and TF (22.23\ub13.00 mgCE/gDL) content between samples obtained at 60, 70 \ub0C and 70 \ub0C under nitrogen flow. During the tea production, within each range of particles size (e.g. B), we found out that decoction is the process that allows to extract the highest quantity of total polyphenols (41.14\ub12.56 mgGAE/gDL) and total flavonoids (45.27\ub13.10 mgCE/gDL)