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- Recovery of bioactive compounds from industrial exhausted olive pomace through ultrasound-assisted extractionPublication . Gómez Cruz, Irene; Contreras, Maria del Mar; Carvalheiro, Florbela; Duarte, Luís C.; Roseiro, Luisa B.; Romero, Inmaculada; Castro, EulogioABSTRACT: Simple Summary Exhausted olive pomace (EOP) is the main residue of the pomace oil extraction industry, which is generated in large quantities and has limited applications. Thus, this study aimed to obtain bioactive compounds from EOP using ultrasound-assisted extraction as a potential first valorization step. Two types of devices were tested: bath- and probe-type UAE. The operational parameters were studied and optimized to maximize the antioxidant compounds. In particular, hydroxytyrosol was the main phenolic compound identified and its content was 5.16 mg/g EOP (bath-type UAE) and 4.96 mg/g EOP (probe-type UAE). Mannitol was also detected in the extract, 59.53 mg/g EOP (bath-type UAE) and 69.73 mg/g EOP (probe-type UAE). The results highlight the great potential EOP has as a source of bioactive compounds, with applicability in several sectors. Moreover, the probe-type UAE shows potential to be applied for obtaining these bioactive compounds in a continuous and faster manner. Exhausted olive pomace (EOP) is the main agro-industrial waste of the olive pomace extracting industries. It contains phenolic compounds and mannitol, so the extraction of these bioactive compounds should be considered as a first valorization step, especially if EOP is used as biofuel. Therefore, EOP was subjected to bath-type ultrasound-assisted extraction (UAE), and the effects of the acetone concentration (20-80%, v/v), solid load (2-15%, w/v), and extraction time (10-60 min) on the extraction of antioxidant compounds were evaluated according to a Box-Behnken experimental design. By means of the response surface methodology, the optimum conditions were obtained: 40% acetone, 8.6% solids, and 43 min. For all the extracts, the total phenolic content (TPC), flavonoid content (TFC), and antioxidant activity (DPPH, ABTS, and FRAP) were determined. With the aim of shortening the extraction time, a two-level factorial experiment design was also carried out using a probe-type UAE, keeping the solid load at 8.6% (w/v) and the acetone concentration at 40% (v/v), while the amplitude (30-70%) and the extraction time (2-12 min) were varied to maximize the aforementioned parameters. Finally, a maximum of phenolic compounds was reached (45.41 mg GAE/g EOP) at 12 min and 70% amplitude. It was comparable to that value obtained in the ultrasonic bath (42.05 mg GAE/g EOP), but, remarkably, the extraction time was shortened, which translates into lower costs at industrial scale. Moreover, the bioactive compound hydroxytyrosol was found to be the major phenolic compound in the extract, i.e., 5.16 mg/g EOP (bath-type UAE) and 4.96 mg/g EOP (probe-type UAE). Other minor phenolic compounds could be detected by capillary zone electrophoresis and liquid-chromatography-mass spectrometry. The sugar alcohol mannitol, another bioactive compound, was also found in the extract, and its content was determined. Thus, the use of this technology can support the valorization of this waste to obtain bioactive compounds, including mannitol, hydroxytyrosol, and other derivatives, before being applied for other uses.
- Strategies for the purification of hydroxytyrosol-rich extracts obtained from exhausted olive pomacePublication . Gómez Cruz, Irene; Contreras, Maria del Mar; Romero, Inmaculada; Ribeiro, Belina; Roseiro, Luisa B.; Duarte, Luís C.; Carvalheiro, Florbela; Castro, EulogioABSTRACT: Exhausted olive pomace (EOP) is a residual biomass from which hydroxytyrosol can be recovered. This compound has applications in the food/pharma sectors, but its extraction yields complex extracts that require further purification for some applications. This work explores purification strategies based on membrane technology, liquid–liquid extraction (LLE), and solid-phase extraction with adsorbents and resins. The hydroxytyrosol content, phenolic profile, antioxidant activity, and inhibition of α-glucosidase and α-amylase were monitored. Hydroxytyrosol stood out in all purified extracts. The best hydroxytyrosol recovery (88.8%) was achieved using LLE with ethyl acetate as the extractant, while the purest extracts in phenolic compounds, including hydroxytyrosol, were obtained using the latter solvent and C18 (529 mg/g), DSC-8 (873 mg/g), and Purosorb PAD910 (523 mg/g). Conversely, mannitol and glucose, at high concentrations in the extract, were selectively retained in the aqueous phases. The developed strategies are discussed regarding their suitability to provide hydroxytyrosol-concentrated extracts, up to 291 mg/g, with antioxidant and antidiabetic functionalities.