RT info:eu-repo/semantics/conferenceObject
T1 Subcritical water extraction of quercetin and derivatives from onion skin wastes (Allium cepa cv. Horcal): effect of temperature and solvent properties
A1 Benito Román, Oscar
A1 Blanco Alcalde, Beatriz
A1 Sanz Díez, Mª Teresa
A1 Beltrán Calvo, Sagrario
K1 Ingeniería química
K1 Chemical engineering
AB Nowadays, the society is immersed in the transition from a linear to a circular economy,in which the value of products, materials and resources is maintained in the economy foras long as possible and the generation of waste is minimized. This means that thebyproduct of a process becomes the input of a new one where it acquires new value.Among other agricultural by-products, onion (Allium cepa L.) skin wastes offer greatpotential for valorization. Onion is the second most important horticultural cropworldwide. More specifically, Spain, in the year 2018 produced 1.27 Mt [1]. The onionindustry generates every year more than 0.5 Mt of Onion Skin Wastes (OSW) worldwide[2], including skins (the outermost layers), roots and bulbs unfit for consumption. Thenon-edible brown skin and external layers of onions are rich in phenolic compounds,mainly flavonoids such as quercetin (QC) [3] and its derivatives: quercetin 4’-O-β-glycoside (QC4’), quercetin 3,4’-O-β-diglycoside (QC3,4’) and quercetin 3-O-β-glycoside (QC3). All of them are high-added value natural antioxidants [2]. The maindrawback of quercetin and quercetin derivatives is the limited solubility in water, whichlimits their oral bioavailability [4] and extractability, and forces the use of an organicsolvent to successfully extract them. Alternatively, Subcritical Water (SubW) can be used to extract flavonoids from onion skins. SubW refers to water at temperatures ranging from100 °C (boiling point) to 374 °C (critical point) which remains in a liquid state due to theapplication of pressure. Changes in the working conditions change the properties of theSubW (among them, viscosity, surface tension and dielectric constant, which can besimilar to those of some organic solvents), enhancing mass transfer and the extractabilityof barely water-soluble bioactive compounds, as summarized by Benito-Roman et al. [5],as SubW favors the hydrolysis of the bonds between phenolic compounds and thevegetable matrix.In this work the extraction, identification and quantification of phenolic compounds fromOSW has been studied using SubW in a semicontinuous extractor (flow rate constant andequal to 2.5 mL/min; temperatures up to 180 °C with working pressure of 5 MPa, to keepwater in liquid state). The extraction of flavonoids resulted to be fast (<30 min) andtemperature sensitive (maximum at 145 °C; total flavonoids, 27.4±0.9 mg/g OSW).Further increases of temperature decreased the number of flavonoids recovered. Theexperimental results were fitted to the Weibull model. The influence of the solventproperties on the flavonoids quantification was found to be critical. A precipitate wasformed once the extracts cooled down. If removed, a significant fraction of the hightemperature extracted flavonoids (as much as 71%, at 180 °C) was lost. This fact affectedespecially to those compounds that show extremely low solubility in water at roomtemperature, whereas quercetin glycosylated derivatives were less affected by the polaritychange of the medium induced by the temperature change. It has been demonstrated thatit is necessary to re-dissolve the subcritical water extracts by the addition of ethanol,which led to a medium with a polarity equivalent to that obtained with water at hightemperature. At 145 °C, quercetin (15.4±0.4 mg/g OSW) and quercetin-4’-glucoside(8.4±0.1 mg/g OSW) accounted for the 90% of the total flavonoids identified by HPLC,according to the method described by Benito-Román et al. [6]. All in all, the obtainedextracts resulted to be rich in flavonoids, which makes them suitable to be used as foodadditives in order to replace other synthetic antioxidant compounds.
YR 2022
FD 2022
LK http://hdl.handle.net/10259/6659
UL http://hdl.handle.net/10259/6659
LA eng
NO Trabajo presentado en: EIFS2022, the 2nd Iberian Meeting on Supercritical Fluids (2º Encontro Ibérico de Fluidos Supercríticos / 2º Encuentro Ibérico de Fluidos Supercríticos), to be held on 28.February - 2.March 2022 in Coimbra, Portugal.
NO This work was supported by AEI [PID2019-104950RB-I00 and PID2020-116716RJ-I00] and JCyL and ERDF [BU050P20] [BU301P18]
DS Repositorio Institucional de la Universidad de Burgos
RD 23-nov-2024