Ultrasound-Assisted Extraction as a First Step in a Biorefinery Strategy for Valorisation of Extracted Olive Pomace

Abstract

Currently, interest in finding new feedstock as sources of natural food antioxidants is growing. The extracted olive pomace (EOP), which is an agro-industrial residue from the olive pomace extracting industries, is generated yearly in big amounts, mainly in the Mediterranean countries. EOP was subjected to an ultrasound assisted extraction with ethanol-water mixtures. The effect of main parameters, such as ethanol concentration (30–70% v/v), ultrasound amplitude (20–80%), and extraction time (5–15 min), on the extraction of antioxidant compounds was evaluated according to a Box–Behnken experimental design. The antioxidant capacity of the resulting extracts was determined by measuring their content in total phenolic compounds (TPC) and flavonoids (TFC), as well as their antioxidant activity by DPPH, ferric reducing antioxidant power (FRAP), and ABTS assays. Considering the simultaneous maximization of these five responses, the optimal conditions were found to be 43.2% ethanol concentration, 70% amplitude, and 15 min. The ultrasound assisted extraction of EOP under these optimized conditions yielded an extract with a phenolic and flavonoid content (per gram of EOP) of 57.5 mg gallic acid equivalent (GAE) and 126.9 mg rutin equivalent (RE), respectively. Likewise, the values for DPPH, ABTS, and FRAP assay (per gram of EOP) of 56.7, 139.1, and 64.9 mg Trolox equivalent, respectively were determined in the optimized extract.

Valorisation of Exhausted Olive Pomace by an Eco-Friendly Solvent Extraction Process of Natural Antioxidants

“…The total phenolic content (TPC) was determined by Folin–Ciocalteu assay [ 32 ] with some modifications as described in Martínez-Patiño et al [ 8 ]. Gallic acid was used as standard and the results expressed as milligrams of gallic acid equivalent (GAE) per gram of EOP.…”

“…Gallic acid was used as standard and the results expressed as milligrams of gallic acid equivalent (GAE) per gram of EOP. Total flavonoid content (TFC) was measured according to Blasa et al [ 33 ], following the methodology described in Martínez-Patiño et al [ 8 ]. The standard reference used was rutin and the results expressed as milligrams of rutin equivalent (RE) per gram of EOP.…”

“…Some of the most worrying emissions related to this biomass are aromatics compounds (benzene, toluene, or phenol), sulphur, chlorine compounds, dioxins and furans, which are considered dangerous to both the environment and human health [ 7 ]. Therefore, the search for alternative uses for this agro-industrial waste is of great interest [ 8 ].…”

“…An interesting method of valorisation of EOP is to obtain high-value bioactive compounds. In this sense, several phenolic compounds with antioxidant potential have been identified in waste generated by the olive pomace oil industry; these include hydroxytyrosol, tyrosol, oleuropein, apigenin, luteolin, and rutin, among others [ 8 ]. These compounds have been proved to have numerous benefits for human health, including anticarcinogenic, antimicrobial, antihypertensive, anti-inflammatory, hypoglycaemic, and hypocholesterolaemic properties [ 9 , 10 ].…”

“…New extraction technologies for olive pomace, such as microwave-assisted extraction, ultrasound-assisted extraction with different solvents [ 16 , 17 , 18 , 19 ], and extraction with natural deep eutectic solvents [ 16 ] have also been reported. Martínez-Patiño et al [ 8 ] reported the recovery of bioactive compounds from EOP using ultrasound-assisted extraction with ethanol–water mixtures. According to these authors, EOP can be considered a promising feedstock for the extraction of bioactive compounds, mainly phenols.…”