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Green Valorization of Olive Leaves to Produce Polyphenol-Enriched Extracts Using an Environmentally Benign Deep Eutectic Solvent

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School of Agricultural Sciences, University of Thessaly, N. Temponera Street, 43100 Karditsa, Greece
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Food Quality & Chemistry of Natural Products, Mediterranean Agronomic Institute of Chania (M. A. I. Ch.), International Centre for Advanced Mediterranean Agronomic Studies (CIHEAM), P.O. Box 85, 73100 Chania, Greece
*
Author to whom correspondence should be addressed.
AgriEngineering 2020, 2(2), 226-239; https://doi.org/10.3390/agriengineering2020014
Received: 17 March 2020 / Revised: 28 March 2020 / Accepted: 30 March 2020 / Published: 1 April 2020
Olive leaves (OLL) are considered to be a highly appreciated bioresource of bioactive polyphenolic phytochemicals, embracing several different structures. However, extraction processes based on deep eutectic solvents (DES) are very limited despite the wide range of techniques developed for the efficient recovery of polyphenols. This study had as objective the development of a simple, green, high-performance extraction methodology for OLL polyphenols, using a recently reported effective DES, composed of L-lactic acid and glycine. Initially, a screening was performed to select the most appropriate L-lactic/glycine molar ratio and process optimization was then carried out with response surface methodology. The optimized process variable values were DES/water (78% w/v), liquid-to-solid ratio of 36 mL g−1, and stirring speed of 500 rounds per minute, and the total polyphenol yield amounted to 97.53 ± 3.54 mg gallic acid equivalents per g dry matter. Extraction with DES at 80 °C did not significantly increase the total polyphenol yield, but it did enhance the total flavonoid yield and antioxidant activity. High-performance liquid chromatography analyses revealed that extraction with the DES resulted in extended oleuropein hydrolysis, to the favor of hydroxytyrosol formation. This finding might have a prospect in using properly tuned DES for polyphenol modification with improved bioactivities. View Full-Text
Keywords: deep eutectic solvents; extraction; olive leaves; polyphenols; waste valorization deep eutectic solvents; extraction; olive leaves; polyphenols; waste valorization
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Kaltsa, O.; Grigorakis, S.; Lakka, A.; Bozinou, E.; Lalas, S.; Makris, D.P. Green Valorization of Olive Leaves to Produce Polyphenol-Enriched Extracts Using an Environmentally Benign Deep Eutectic Solvent. AgriEngineering 2020, 2, 226-239.

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