Enhanced-performance extraction of olive (Olea europaea) leaf polyphenols using L-lactic acid/ammonium acetate deep eutectic solvent combined with β-cyclodextrin: screening, optimisation, temperature effects and stability

This investigation had as objective to study the effective recovery of olive leaf (OLL) polyphenols using a blend of an L-lactic acid/ammonium acetate deep eutectic solvent (DES) with beta-cyclodextrin (beta-CD). Following an initial DES screening, the extraction process was optimised with response surface methodology by implementing Box-Behnken design. The optimised extraction conditions thus determined were stirring speed 300 rpm, DES concentration 56.4% (w/w), liquid-to-solid ratio 100 mL g(-1)and beta-CD concentration 0.7% (w/v). Maximum extraction yield (113.66 mg caffeic acid equivalents g(-1)dry mass) was achieved at 80 degrees C, without compromising antioxidant activity. Comparative assessment of the extraction medium DES/beta-CD with other green solvents showed that it was a high-performing system providing polyphenol-enriched extract with improved antioxidant characteristics. Stability test of the extract obtained under optimal conditions performed over a period of 30 days at ambient conditions revealed that, while ferric-reducing power fluctuated within narrow limits, the antiradical activity was enormously enhanced by 100%. These changes in the antioxidant activity were not associated with the decline of major polyphenols in the OLL extract. However, the overall polyphenolic profile remained largely unchanged. It is suggested that the DES/beta-CD is an efficient green solvent that may confer the OLL polyphenol extract satisfactory stability.

Automated summary

This study aimed to optimize the extraction of olive leaf polyphenols using a blended solvent system of L-lactic acid/ammonium acetate DES with beta-cyclodextrin. The optimized conditions resulted in high extraction yield and improved antioxidant activity, with the stability of the extract maintained over a 30-day period. The DES/beta-CD system proved to be an efficient green solvent for the satisfactory recovery of OLL polyphenols.