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Abstract
Olive leaves (OLL) are an agri-food waste that may be regarded as a bioresource rich in bioactive polyphenolic metabolites. In this examination, simultaneous organosolv treatment/extraction of OLL polyphenols at elevated temperatures (>110 °C) has been optimized using glycerol, but also two glycerol-based deep eutectic solvents (DES). The assessment of the processes was based on the severity factor and the extraction efficiency factor. In any case, the treatment/extraction with a DES composed of glycerol and citric acid (GL-CA) was found to be the less severe and the most effective in recovering polyphenols from OLL, giving a yield of 69.35 mg gallic acid equivalents per g dry mass. On the other hand, liquid chromatography-mass spectrometry investigation revealed that extraction with either DES used provided extracts with differentiated polyphenolic profile than that obtained when water or 60% (v/v) aqueous ethanol was used as solvents. On the ground of these analysis, evidence emerged regarding hydrolysis of flavone glucosides when the treatment was performed with an alkaline DES composed of glycerol and sodium citrate. The extracts produced also exhibited diversified antioxidant activity, a fact putatively attributed to the different polyphenolic profiles. It was concluded that organosolv treatment/extraction of OLL for polyphenol recovery opens new endeavors in the valorization of this particular waste, but metabolite stability is an issue that merits profounder study.
Highlights
Published: 7 March 2022According to recent estimations, about 140 billion tons of biomass are generated globally per annum from the agricultural sector [1]
The antioxidant activity expressed by Olive leaves (OLL) extracts has been mainly atTo the best of the authors’
7-O-glucoside [38,39], and it would appear that the differences found in the chromatoAppraisal the processes tested based extractioncharacteristics
Summary
About 140 billion tons of biomass are generated globally per annum from the agricultural sector [1]. A considerable part of this biomass is characterized as waste, comprised mainly of leaves, seeds, peels, roots, stalks, small branches, straw residues, etc. These agri-food side streams may pose severe environmental concerns, if not properly managed and disposed, yet they are recognized as bioresources to produce bioenergy, feed, fertilizers, platform chemicals and high valueadded commodities. The orientation of the global economy towards sustainable routes has enabled the implementation of alternative strategies, aimed at minimizing the volume of non-renewable materials used today, and valorize waste biomass in a biorefinery concept [2,3]. A plethora of polyphenolic substances has been demonstrated to possess biologically important activities, including mainly antioxidant, anti-inflammatory and antimicrobial effects, and
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