Comparison between different liquid-liquid and solid phase methods of extraction prior to the identification of the phenolic fraction present in olive oil washing wastewater from the two-phase olive oil extraction system

Abstract

SUMMARY:Phenolic compounds from olive mill wastewater (OMW), are characterized by a strong antioxidant activity. At the same time, they represent an environmental problem because they are difficult to degrade. The purpose of this work was to identify these biologically active compounds in the OMW from two-phase olive oil production in order to convert a polluting residue into a source of natural antioxidants. After optimizing the extraction process of phenolic compounds using liquid-liquid extraction (LLE) and solid phase extraction (SPE) methods, it was determined that the most appropriate sequence comprised a previous centrifugation to remove the lipid fraction, followed by liquid extraction with ethyl acetate or SPE. The most important compounds identified in olive oil washing wastewater (OOWW) were tyrosol, hydroxytyrosol and succinic acid; whereas the ones in the wastewater derived from the washing of the olives (OWW) were cresol, catechol, 4-methylcatechol, hydrocinnamic acid and p-hydroxy-hydrocinnamic acid. KEYWORDS: Antioxidants; Ethyl acetate; Extraction; Hydroxytyrosol; Olive oil wastewater; PolyphenolsRESUMEN: Comparación entre métodos de extracción líquido-líquido y en fase sólida previos a la identificación de la fracción fenólica presente en las aguas residuales procedentes del lavado del aceite de oliva obtenido mediante el sistema de extracción de aceite de oliva en dos fases. Los compuestos fenólicos presentes en las aguas residuales de la industria oleícola (OMW) se caracterizan por una gran actividad antioxidante. Por otra parte, suponen un problema medioambiental debido a que son difíciles de degradar. El objetivo de este trabajo fue la identificación de estos compuestos biológicamente activos que se encuentran en las OMW generadas del proceso de obtención del aceite de oliva por el sistema de dos fases, para así convertir un residuo contaminante en una fuente de antioxidantes naturales. Tras optimizar el proceso de extracción de los compuestos fenólicos utilizando extracción líquido-líquido (LLE) y extracción en fase sólida (SPE), se obtuvo que la secuencia más apropiada comprendió una centrifugación previa para eliminar la fracción lipídica, seguida de una extracción líquida con acetato de etilo o una SPE. Los compuestos más importantes identificados en las aguas residuales del lavado del aceite de oliva (OOWW) fueron tirosol, hidroxitirosol y el ácido succínico, mientras que los de las aguas residuales derivadas del lavado de las aceitunas (OWW) fueron cresol, catecol, 4-metilcatecol, ácido hidrocinámico y ácido p-hidroxi-hidrocinámico.

Antioxidant quantification in different portions obtained during olive oil extraction process in an olive oil press mill

“…Ciciarello samples showed instead a different trend of this compound, that was more abundant in P of both harvesting periods, denoting a different varietal response linked to the different initial oleuropein concentration in drupes, varying in parallel with the hydrolysis of that compound of higher molecular weight. Tyrosol is another important antioxidant, derived by oleuropein metabolism with essential health properties for humans: 15 among the considered olive by‐products that can be valorized for biophenols recovery, the highest quantities were quantified in OWW of Tonda di Filogaso and Ottobratica collected at November (36.31 mg L −1 and 34.97 mg L −1 , respectively). Around 10 mg L −1 of tyrosol were instead quantified in OWW of Ottobratica Calipa and in P of Ciciarello, as more abundant contents.…”

“…Oleuropein is the major phenolic compound in olive pulp, with relatively high levels in immature olive fruit that decline during the physiological development of the fruit in correspondence to the green and black maturation phases 13 . Olive mill wastewaters contain several phenolic compounds among which tyrosol, hydroxytyrosol, and oleuropein are the main components: their extraction has been investigated in the literature 14,15 . The recovery of bioactive compounds from wastes could be very important to convert them into a resource of natural antioxidants: they can be reused in different applications such as in food (as preservatives) and in pharmaceutical industries (for human disease prevention), helping the sustainability of the olive oil production management.…”