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

Abstract

A series of citrate salts were tested as hydrogen bond acceptors to synthesize deep eutectic solvents (DES) based on lactic acid and glycerol, used as hydrogen bond donors. The DES produced were then screened to identify the highest performing system for the effective extraction of polyphenolic phytochemicals from the medicinal plant Salvia fruticosa Mill. (Greek sage). The most efficacious DES was the one composed of lactic acid and sodium citrate dibasic, at a molar ratio of 15:1 (LA-SCDB15). Furthermore, for the first time there has been evidence concerning DES pH and extraction efficiency. Using this solvent, a batch, stirred-tank extraction process was developed, by employing ultrasonication pretreatment and response surface methodology. The optimal settings determined were stirring speed 900 rpm, proportion of DES/water 77% (w/v), and ultrasonication pretreatment time 15 min. By adjusting these optimal settings, the predicted maximum total polyphenol yield was calculated to be 79.93 ± 1.92 mg gallic acid equivalents g−1 dry mass. The examination of temperature effects demonstrated that the batch, stirred-tank extraction stage was very energy-efficient, with a barrier of 7.64 kJ mol−1. Comparison of the extraction of Salvia fruticosa polyphenols with other green processes previously developed, illustrated the high extraction capacity of LA-SCDB15. The major polyphenols identified in the extracts produced under optimized settings were chlorogenic acid, luteolin 7-O-glucuronide and rosmarinic acid.

Glycerol and Glycerol-Based Deep Eutectic Mixtures as Emerging Green Solvents for Polyphenol Extraction: The Evidence So Far

“…leaves was shown to occur with glycerol/sodium acetate at a molar ratio of 6 [ 82 ], whereas lower or higher molar ratios were not favorable in this regard. Such a behavior was confirmed by several following studies employing DES composed of glycerol/L-alanine [ 74 ], glycerol/nicotinamide [ 76 ], glycerol/sodium propionate [ 75 ] and glycerol/citrates [ 83 ]. Finally, another study on glycerol-based DES with sodium acetate, sodium propionate and sodium butyrate, illustrated that the longer the carbon chain length of the HBA, the higher the amount of water required in the DES/water mixture to attain maximization of polyphenol extraction from Origanum dictamnus [ 73 ].…”

“…Yet, glycerol/sodium acetate (5/1) outperformed L-lactic acid/sodium acetate (5/1) in total flavonoid extraction [ 84 ]. In another study, a series of DES based on glycerol and L-lactic acid as HBDs, and sodium citrate salts as HBAs, were synthesized and screened for their efficiency in extracting polyphenols from Salvia fruticosa Mill [ 83 ].…”

Stability of Salvia fruticosa Mill. polyphenols and antioxidant activity in a citrate-based natural deep eutectic solvent

“…2,4,6-Tripyridyl-s-triazine (TPTZ) (98 %), acetic acid, methanol and iron chloride hexahydrate were from Honeywell/Fluka (Steinheim, Germany). The deep eutectic solvent (DES), composed of lactic acid (LA) and sodium citrate dibasic (SCDB) at a molar ratio of 15 : 1, was synthesized as described earlier (Grigorakis et al 2020b). The DES was used as aqueous mixture (77/23 w/w).…”

“…Extraction of S. fruticosa was performed using the optimized process, as reported elsewhere (Grigorakis et al 2020b). In short, 0.375 g of dried plant material was mixed with 15 mL 77 % (w/w) DES/water and ultrasonicated for 15 min in an ultrasonication bath (Sonorex Bandeline, Berlin, Germany), at room temperature (23 ± 2 C).…”

“…Polyphenols are inherently molecules prone to oxidation and/or other structural modifications, and thus the study of polyphenol stability under a given set of conditions is of paramount importance. Recently, our group reported the use of a novel DES, coded LA-SCDB15, which displayed very high performance in the extraction of polyphenols from S. fruticosa (Grigorakis et al 2020b). To further appraise the applicability of this solvent in the generation of polyphenolenriched extracts, this study was undertaken to examine the stability of S. fruticosa polyphenols in extracts produced using LA-SCDB15.…”