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

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.

Batch Stirred-Tank Green Extraction of Salvia fruticosa Mill. Polyphenols Using Newly Designed Citrate-Based Deep Eutectic Solvents and Ultrasonication Pretreatment

“…The outcome presented in Tables 4 and 5 pointed out the higher efficiency of LA-SCDB15 and it was in line with earlier examinations, which demonstrated that polyphenol extraction with DES was more effective than those performed with common conventional solvents, such as aqueous methanol or ethanol [16,21,23,24]. At this point it should be stressed that the content of S. fruticosa in certain…”

“…The linear regression gave R 2 = 0.67 (p = 0.0003), revealing a trend that should not be overlooked, which evidenced higher extraction efficiency for DES with lower pH. Although previous studies on polyphenol extraction with DES stressed emphatically the importance of R mol D/A on the extraction yield [16,[21][22][23][24], a correlation of yield with pH is heretofore unreported. As also reported for classical solvents, pH is critical for DES extraction efficiency.…”

“…Since LA-SCDB15 provided significantly higher Y TP compared to all other DES tested, this solvent was chosen to further optimize the extraction process. To this end, three process variables that can critically affect polyphenol extraction [16,21,24], namely the S S , the C DES and the t US , were included in the experimental design. The design deployed aimed at assessing the effect of the process variables and identifying any synergistic functions between them.…”

Pulsed Electric Field and Salvia officinalis L. Leaves: A Successful Combination for the Extraction of High Value Added Compounds

“…The method was adapted from Kaltsa et al [ 29 ]. In brief, a Shimadzu liquid Chromatograph (CBM-20A) and a Shimadzu detector (SPD-M20A) were used.…”

Essential Oil Content of Baccharis crispa Spreng. Regulated by Water Stress and Seasonal Variation

“…High water stress levels affect oil yield in many aromatic plants [11,12]. Metabolites and essential oil yields in different medicinal and aromatic plants decrease under water-stress conditions [10,[13][14][15][16] and reduced irrigation frequency [11,12,17]. B. crispa is popularly recognized as carqueja in Brazil, and grows spontaneously in a wide range of soils and ecosystems in different Brazilian bioclimatic zones [18].…”