Abstract
Olive-derived biomasses contain bioactive compounds with health promoting effects as well as antioxidant and sweet-tasting properties. However, their sequential extraction has not been attained. In the present study, firstly antioxidants and mannitol were extracted from exhausted olive pomace (EOP) by an eco-friendly method, ultrasound-assisted water extraction (UAWE). The amplitude (20–80%), extraction time (2–18 min) and solid loading (2–15%, w/v) were evaluated according to a Box–Behnken experimental design. Using the response surface methodology, the optimal conditions for extraction were obtained: 80% amplitude, 11.5% solid loading and 16 min. It enabled the multi-response optimization of the total phenolic content (TPC) (40.04 mg/g EOP), hydroxytyrosol content (6.42 mg/g EOP), mannitol content (50.92 mg/g EOP) and antioxidant activity (ferric reducing power or FRAP, 50.95 mg/g EOP; ABTS, 100.64 mg/g EOP). Moreover, the phenolic profile of the extracts was determined by liquid chromatography-UV and mass spectrometry, identifying hydroxytyrosol as the main phenolic compound and other minor derivatives could be characterized. Scanning electron microscopy was used to analyze the morphological changes produced in the cellular structure of EOP after UAWE. In addition, the chemical composition of the extracted EOP solid was characterized for further valorization. Then, a second extraction step was performed in order to extract bioactive triterpenes from the latter solid. The triterpenes content in the extract was determined and the effect of the previous UAWE step on the triterpenes extraction was evaluated. In this case, the use of ultrasound enhanced the extraction of maslinic acid and oleanolic acid from pelletized EOP with no milling requirement. Overall, UAWE can be applied to obtain antioxidant compounds and mannitol as first extraction step from pelletized EOP while supporting the subsequent recovery of triterpenic acids.
Highlights
Hydroxytyrosol is one of the natural antioxidants present in olive-derived biomasses and olive oil [1]. It is found in different by-products/wastes obtained during olive oil and pomace olive oil production such as olive leaves, olive pomace, exhausted olive pomace (EOP) and olive mill wastewater [2]
Ultrasound is an efficient technique for the extraction of phenolic compounds from olive-derived biomasses in a short time [11,34,35], in these works, alcoholic solutions were applied as extractive agents
In a previous work on EOP, it was evidenced that water can be applied to extract hydroxytyrosol from EOP but a relatively high temperature
Summary
Hydroxytyrosol is one of the natural antioxidants present in olive-derived biomasses and olive oil [1]. It is found in different by-products/wastes obtained during olive oil and pomace olive oil production such as olive leaves, olive pomace, exhausted olive pomace (or extracted olive pomace, defatted olive pomace) (EOP) and olive mill wastewater [2]. The healthy benefits of hydroxytyrosol have been shown in clinical trials [6]. It protects against lipid oxidation and prevents cardiovascular disease [6] and in combination with vitamin E improves steatosis and hypertriglyceridemia in children [7]. A health claim has been published by the European Food Safety Authority (EFSA) on the bene-
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