Historically, the white mulberry (Morus alba) has been widely used as part of Chinese traditional medicine, in addition to sericulture. It is a rich source of bioactive compounds that exhibit many physiological and pharmacological effects. Conventional organic solvents used in their extraction are a problem, as they are not desirable due to their relative toxicity. Deep eutectic solvents (DES) are a potential green alternative.
The aim of my research work was to verify the efficiency of selected DES in comparison to traditional organic solvents in the extraction of bioactive compounds from white mulberry. To this end, I developed an HPLC-DAD method for the determination of selected polyphenols, limiting myself to gallic acid, caffeic acid, p-coumaric acid, rutin and resveratrol. As part of the partial validation, linearity, repeatability, limit of detection, limit of quantification, accuracy and selectivity were checked. The bioactive compounds were extracted from a sample of white mulberry branches by ultrasound-assisted extraction (UAE), optimised using choline chloride/glycerol DES. Based on the results, the determined optimal conditions were: 1:2 molar ratio, 20% added water, 80 °C and 30 min. For subsequent extractions 6 different DES based on choline chloride (ChCl) as hydrogen bond acceptor were prepared. The hydrogen bond acceptors used included glycerol, ethylene glycol, propane-1,3-diol, butane-1,4-diol, urea and glucose. Methanol was used as the conventional organic solvent. Extracts were prepared from the branches, leaves and fruits of white mulberry and the extraction efficiencies were evaluated in three different ways. In addition to the analysis by the developed HPLC-DAD method, total phenolic content (TPC) and total flavonoid content (TFC) were also determined. The results obtained showed that DES based on polyalcohols as hydrogen bond donors were the most efficient. In the case of branches and leaves, it was the ChCl/glycerol DES, while for fruits it was the ChCl/ethylene glycol DES. In most of the tested polyphenol extractions, at least one DES achieved comparable or higher extraction efficiencies than the organic solvent, except in the case of flavonoids, where DES yields were often lower. This indicates the potential of using DES as an alternative procedure for the green and efficient extraction of polyphenolic bioactive compounds from plant materials such as white mulberry.
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