Physicochemical and Antimicrobial Properties of Lactic Acid-Based Natural Deep Eutectic Solvents as a Function of Water Content  
[PERSON]  
1 Murmansk Marine Biological Institute of the Russian Academy of Sciences (MMIRI RAS), Vladimirskaya Str., 17, 18308 Murmansk, Russia; [EMAIL_ADDRESS] (O.N.P.); [EMAIL_ADDRESS] (E.D.O.) Department of Microbiology and Biochemistry, Murmansk Arctic University, Institute of Natural Sciences and Technology, Kapienza Serova Str., 15, 18308 Murmansk, Russia; [EMAIL_ADDRESS]  
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[PERSON]  
1 Murmansk Marine Biological Institute of the Russian Academy of Sciences (MMIRI RAS), Vladimirskaya Str., 17, 18308 Murmansk, Russia; [EMAIL_ADDRESS] (O.N.P.); [EMAIL_ADDRESS] (E.D.O.) Department of Microbiology and Biochemistry, Murmansk Arctic University, Institute of Natural Sciences and Technology, Kapienza Serova Str., 15, 18308 Murmansk, Russia; [EMAIL_ADDRESS]  
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[PERSON]  
3 Department of Technology of Pharmaceutical Formac  
use requires special care due to their high volatility, explosiveness, fire hazard, and toxicity to humans, flora, and fauna. Traditionally used organic solvents are not biodegradable and cause toxicity and carcinogenicity for live organisms and environmental toxicity [1]. The reduction of the use and production of hazardous substances in industry, decrease in energy consumption, and switching to renewable sources are the main challenges of green chemistry. To protect human health and the environment from the risks related to toxic reagents, many efforts are focused on the quest for alternative green solvents [2].  
Recently, a new class of deep eutectic solvents (DESs) has attracted the vigorous attention of the scientific community as a promising alternative to organic solvents [3; 4]. DESs were first proposed at the beginning of the XXI century by [PERSON] et al. (2004) as a biodegradable green alternative to organic liquids [5]. DESs are systems obtained by the interaction of a hydrogen bond donor (HBD) with a hydrogen bond acceptor (HBA) through hydrogen bonds to form a eutectic mixture [6]. The special term, natural deep eutectic solvent (NADESs), was proposed for DESs prepared from components that represent normal metabolites of live cells [7; 8; 9].  
Although NADESs are a relatively young group of solvents, different classes of plant metabolites, such as alkaloids [10], anthocyanins [11], carotenoids [12], coumarins [13], isoflav [14], polyphenols [15], steroidal [16] and triterpene saponins [17], and polysaccharides [18], were successfully extracted from plants. High viscosity is one of the limitations of NADES. The high viscosity of NADES slows solvent penetration into the plant matrix, mass transfer when dissolving metabolites within plant cells, and transfer of extract within the solvent [19]. This problem could be overcome by increase of temperature, stirring [12], in-process grinding of plant material in vibrocavitation equipment [17], application of ultrasound waves [11], or microwaves [10]. Another efficient way to decrease their viscosity is dilution by water [11; 13; 14; 19; 20]. Even though many commonly used NADESs are prepared from components that could be consumed by microorganisms, several publications report some antimicrobial activities of NADES. However, this aspect has not been sufficiently studied. Water is used for the tuning of NADES properties. The systematic study of the effect of water content on the properties of NADES and their antimicrobial activity is required.  
In this paper, we characterized the physicochemical and antimicrobial properties of NADES, composed of lactic acid in combination with sorbitol, glucose, and choline chloride, depending on the water content in NADES.