Abstract
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.
Highlights
Food production inevitably leads to waste generation at every processing stage
The process design was implemente using response surface methodology and extraction appraisal was based on total polyphenol yield, in vitro antioxidant properties of the extracts, as well as the profiling of major polyphenolic metabolites
The proportion of deep eutectic solvents (DES) and water is another key parameter related with the extraction of Olive leaves (OLL) polyphenols and this has been unequivocally demonstrated by recent studies [24,25,26]
Summary
Food production inevitably leads to waste generation at every processing stage. This residual biomass is mostly composed of organic substances and it is characterized by a significant polluting load, high moisture content, variable composition, and creates disposal management problems of paramount importance [1]. Selection is principally associated with the green profile of the process as a whole, and critical parameters, such as the physical–chemical characteristics of the compounds of interest, selectivity, high recovery yields, and stability of the target compounds, are the key criteria considered. On such a basis, deep eutectic solvents (DES) are promising materials, which are characterized by several advantages over conventional, volatile solvents of petrochemical origin. The process design was implemente using response surface methodology and extraction appraisal was based on total polyphenol yield, in vitro antioxidant properties of the extracts, as well as the profiling of major polyphenolic metabolites
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