Instant controlled pressure drop texturing for intensifying ethanol solvent extraction of olive (Olea europaea) leaf polyphenols

In this work, the process of “Détente Instantanée Contrôlée”: DIC (French for Instant controlled pressure drop) assisted to ethanol solvent extraction of phenolic compounds of olive (Olea europaea) leaves was studied. Response surface methodology (RSM) was used to optimize the conditions of solvent extraction carried out on the raw material, as well as the operating parameters DIC texturing taking place as pretreatment; both for getting the highest extraction yields of total phenolic compounds (TPC). The studied parameters were the ethanol concentration in the aqueous solution (S), the temperature (T) and the liquid/solid ratio (r). The maximum yield was 49.84 mg GAE per g of dry raw material, and the optimal conditions were: 95.6% EtOH, 55 °C and 40 ml g−1 dm. Under these optimal solvent extraction conditions of the polyphenols extraction, RSM was also used for optimizing DIC treatment. The total phenolic compounds yield of dry DIC-textured material was higher than that of untreated material with an optimized value of 248.6 mg GAE g−1 at the following conditions: saturated steam pressure: P = 0.1 MPa, number of cycles C = 1 and thermal treatment time t = 11 s. Ultra Performance Liquid Chromatography analysis (UPLC) of the treated and untreated olive leaf extracts revealed that the principal polyphenols were oleuropein, verbascoside, luteolin-7-glucoside and smaller amounts of hydroxytyrosol, apigenin-7-glucoside, tyrosol, vanillic acid and vanillin. Scanning electron microscopy (SEM) showed that, after DIC treatment, there is a change in the structure of olive leaves cells with a destruction of cell walls in comparison with untreated leaves.