Development of green high performance solid-liquid extraction processes for the recovery of antioxidant polyphenols from the medicinal plant Salvia fruticosa Mill. (Cretan sage)

Abstract

In the present work, the efficient extraction of polyphenols from the medicinal plant S. fruticosa Mill., was studied. For this purpose, environmentally benign solvents, additives and techniques were employed while optimization of extraction parameters secured the quantitative recovery of the biomolecules. The extractions performed were evaluated through antioxidant and kinetic assays. In the first part, 3 cyclodextrins, namely β-cyclodextrin (β-CD), methyl-β- cyclodextrin (m-β-CD), and hydroxypropyl-β-cyclodextrin (HP-β-CD) were used as extraction booster of polyphenols from the S. fruticosa plant. The concentration of cyclodextrins (CCD), the pH, and the liquid-to-solid ratio (Rl/s) were optimized by a Box-Behnken experimental design and kinetic study implemented to assess the effect of temperature on the extraction yield. According to the results, the m-β-CD was proved the most effective and the least energy demanding extraction booster. The phenolic profile analysis revealed that the major compounds of the phenolic fraction of the S. fruticosa species were Rosmarinic acid and Luteolin-7-O-glucuronide. In the second part, the extraction capacity of a hydroglycerolic solution was tested and the effect of ultrasound pretreatment was also assessed, for the extraction of polyphenols from the S. fruticosa plant. The results showed that sonication pretreatment contributes to the overall extraction procedure and the time of the sonication affects, also, the phenolic yield. The combined extraction method (sonication + solvent extraction) exhibited comparable results to the previous cyclodextrin boosted extraction utilizing lower temperatures. In the third part, novel deep eutectic solvents (DESs) were synthesized, the hydrogen bond donors (HBD) employed were glycerol (GL) and lactic acid (LA), while the hydrogen bond acceptors (HBAs) were citrate salts. After an initial screening, the most effective DES in terms of extraction capacity of S. fruticosa polyphenol, was the Lactic acid - Sodium citrate dibasic mixture, at molar ratio 15-1 (LA-SCDB15). The optimization of the extraction procedure with a Box-Behnken experimental design and the kinetic assay implemented, revealed that the DES presented higher extraction efficiency for the major salvia polyphenols and more energy efficient in comparison to the previously studied methods. In the fourth and last part, the long-term and accelerated stability of the LA-SCDB15 extract were evaluated. As stability indexes, the antiradical activity (AAR) and ferric reducing power (PR), were used. The results of both assays showed that the DES extracts were stable under the tested conditions. Τhe LC-DAD-MS analyses showed that the major compounds of the salvia species were unaffected by the stability study conditions employed.