Potential application of green extracts rich in phenolics for innovative functional foods: Natural deep eutectic solvents as medium for isolation of biocompounds from berries

Abstract

Natural Deep Eutectic Solvents (NADES) are novel and promising solvents for green extraction of phytochemicals from food and agricultural products. NADES are made of natural origin compounds that are connected via hydrogen bond and have unique tuneable properties1. Numerous studies investigated the extraction of bioactive compounds using NADES resulted in better extraction efficiency compared to conventional solvents, suggesting large potential of these solvents2,3. Low-toxicity, natural origin and affordability of NADES-based extracts enables their application as a preservative in the food industry or functional ingredient of food supplements. The aim of this study was to develop an efficient eco-friendly method for the extraction of phenolic compounds from berries, blueberry, chokeberry and black goji berry, using NADES. This goal will be achieved through investigation of extraction efficiency of applied NADES based on three different approaches, a) chromatographic, through high-performance thin layer chromatography (HPTLC) fingerprint analysis, ultra-high-performance liquid chromatography with a diode array detector and a triple-quadrupole mass spectrometer (UHPLC-DAD-MS/MS) target analysis and bioautography, b) spectroscopic, through quality control parameters, total phenolic content (TPC), total flavonoid content (TFC) and radical scavenging activity (RSA), and c) microbiological, through well diffusion method and minimum inhibitory concentration (MIC). In this study, 36 NADES mixtures, prepared from primary plant metabolites, were tested as green alternatives for extraction of phenolics from three berries. Different hydrogen-bond acceptors (HBA), such as choline chloride, L-proline, L-glycine, and L-lysine were mixed with various hydrogen-bond donors (HBD), four organic acids, two sugars, glycerol and urea, at various molar ratios for NADES preparation. Guided by the fact that extraction efficiency depends on polarity, viscosity and dissolving ability of solvents4, the influence of HBA, HBD and water content were investigated. Methanol, as conventional solvent, was used as contrastive solvent. Choline chloride-based NADES in combination with malic acid, glycerol or urea showed as most efficient. All groups of studied NADES showed various extraction capabilities for phenolic compounds based on chromatographic evaluation and spectrophotometric tests. These results indicate great power of NADES solvents towards selective extraction of phenolics and shows that NADES are designer solvents. Appropriate selection of components for NADES preparation can result in selective extraction of specific phenolic compounds, regardless of how similar structures of targeted compounds are or how complex the matrix is, which gives a significant advantage for application of NADES.