## 1 Introduction  
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 now 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. Consumer trends for natural commodities with health-promoting activities has raised awareness and high demand for botanical-based supplements, and ignited a large development of novel products, thus enabling the launch of a variety of functional ingredients [2] and cosmetic additives [3].  
Currently, 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. Such a solvent should be non-toxic, it should have satisfactory extraction efficiency, it should be inexpensive and readily available, and it should originate from recyclable materials, such as waste biomass [6; 7].  
Deep eutectic solvents (DES) are innovative liquids, composed of low-cost, non-toxic and recyclable materials, which can be naturally occurring compounds (e.g., organic acids and salts, polyols, sugars, etc.). DES are usually composed of a substance functioning as hydrogen bond donor (HBD) (e.g., glycerol, organic acids) and another one as hydrogen bond acceptor (HBA) (e.g., choline chloride, amino acids), and their synthesis is straightforward and benign. DES possess features such as absence of flammability water (im)miscibility and low vapor pressure, and these attributes make DES suitable solvents for a spectrum of sustainable applications, such as extraction, synthesis, etc. [8]. To-date, by virtue of their unique properties, the use of DES for natural product extraction has been rapidly expanding, and there has been a bewildering number of substances used for DES synthesis.  
The family of Lamiaceae is widespread and embraces 220 genera and 4000 species occurring around the globe. The chemistry of Lamiaceae species is exceptionally wide and versatile, as it concerns chemical constituents such as terpen (diterpenes and triterpenenes) and polyphenols, two major and multitudinous groups of biologically active compounds. _Salvia_ L. is the largest genus of the Lamiaceae, represented by over than 1000 species [9; 10]. _Salvia fruticosa_ (syn. _S. triloba_), is known as Greek or Cretan sage, and it is a Lamiaceae species occurring in several parts of the East Mediterranean. A number of biological properties have been ascribed to this medicinal plant, which are mainly attributed to its polyphenic load and composition [11; 12; 13]. However, up to now the development of green extraction processes for the production of polyphenol-containing bioactive extracts from _S. fruticosa_ is extremely limited. 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.