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.
Highlights
Medicinal and aromatic plants (MAPs) are routinely used as food and folk remedies for centuries worldwide, and to-date substantial scientific evidence has accumulated to support their reputed nutritional and pharmacological properties
The knowledge derived by long-term traditional uses of MAPs has been acknowledged as a sound basis to support health claims for numerous botanicals [1], and there has been a climbing interest for products originating from MAPs with a spectrum of bio-functionalities
Precise mass of hydrogen bond donor (HBD) and hydrogen bond acceptor (HBA) were mixed at various molar proportions, and the mixtures were heated at 70 ◦ C, under continuous stirring at 500 rpm, until the formation of perfectly transparent liquids
Summary
Medicinal and aromatic plants (MAPs) are routinely used as food and folk remedies for centuries worldwide, and to-date substantial scientific evidence has accumulated to support their reputed nutritional and pharmacological properties. There is a great interest for the development and implementation of cutting-edge sustainable extraction methods for polyphenols from medicinal plants. In this direction, numerous green and low-cost approaches have gained acceptance as being more efficient and precise than traditional ones [4,5]. In compliance with green chemistry principles, a crucial concern towards establishing eco-friendly extraction processes is the replacement of conventional petroleum-based volatile solvents with bio-based alternatives. In this line, the utilization of a benign, eco-friendly solvent is of prime importance to the sustainable profile of an extraction process. Given the current expanding interest by several cosmetics and food supplement industries in Greece for this particular botanical, the current study had as objective the establishment of a batch stirred-tank green extraction methodology, by blending ultrasonication pretreatment and a highly efficacious DES, selected out of a thorough screening
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