Enhancement of propolis food preservation and functional ingredient characteristics by natural eutectic solvents extraction of phytochemicals

Due to the promising applications of propolis as a natural food preservative, functional ingredient or supplement, on one side, and the inherent toxicity and high volatility of organic solvents used for extraction of phenolics from propolis, a range of natural eutectic solvents (NESs) was evaluated for the extraction of phenolic compounds from poplar type propolis to create "green-labelled" food products. The phenolic profile of novel green propolis extracts was evaluated using high-performance thin-layer chromatography, while 16 phenolic compounds were quantified by ultra-high-performance liquid chromatography hyphenated with mass spectrometry. Pinocembrin and chrysin were the most dominant phenolics with an average concentration of 3111 and 3039 mg/kg in lactic acid-based NES, respectively. Biological activity, such as antioxidative and antimicrobial activities, were determined using spectrophotometric and well diffusion methods. Considering all spectrophotometric assays lactic acid-based presented as the best extraction medium for phenolic extraction, with TPC, TFC and RSA values 150.0 mg GAE/g, 190.0 mg RUE/g, and 132.8 mg TE/g on average, respectively. From 38 studied NESs, cholinechloride:tartaric acid (1:1 n/n), glycerol:lactic acid (1:1 n/n) and glycine: lactic acid (1:3 n/n) were the most promising extraction medium for obtaining the propolis extracts enriched with bioactive compounds. Additionally, proposed green solvents were proved to be the designer solvents and showed potential to be tuned to target specific phenolic compounds. Improved, or at least maintained, biological activity of NES propolis extracts support its application in agriculture industry.