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Extraction of polyphenols from flaxseed cake with green solvents assisted with microwaves and ultrasound

Nutritional value of flaxseed could be singled out in three major compounds: oil with dominant alpha linolenic fatty acid, fibers and polyphenols in form of glucosides, mostly lignans. Quantity of lignans in flaxseed is far greater than any other natural source but during oil extraction process polyphenols are left in press cake which is rarely used for human consumption. Lignans show significant biological activity through their derivates formed in our gut by intestinal bacteria. Apart from lignans, other detected phenols in flaxseed include ferulic and p-coumaric acid glucosides. Current methods of polyphenol extraction from flaxseed are time consuming (6h or more) and use organic solvents which mixed with NaOH which have negative impact on an environment. Deep eutectic solvents (DES) present inexpensive and ecological alternative to organic solvents while their role will be attractive not only for academic and medicinal research but also for industrial research. Combination of microwave and ultrasound extraction with deep eutectic solvents replacing organic solvents opens new possibilities in significantly improving this process. In this research, we tried to replace organic solvents with different DES and compare the results with some standard methods. Four different DES mixtures with alkaline properties were used for extraction: choline chloride:urea:glycerol, choline chloride:ethylene glycol, choline chloride:urea:ethylene glycol and choline chloride:urea with different 0.1 M NaOH ratios. Combination of microwave and ultrasound extraction showed better results compared just with microwaves while higher NaOH ratios (from 30 up to 50 %) had significant influence on quantity of extracted polyphenols. Much better results were obtained with ferulic and p- coumaric acid glucosides then with lignans. Up to 50 % of them were extracted compared with standard methods while lignan recovery was closer to 20 %. While this method needs further improvement and optimization the most promising solvents are choline chloride:urea:glycerol and choline chloride:ethylene glycol with 40 % of 0.1 M NaOH, extraction time of 6 minutes and microwave power 200W for choline chloride:urea:glycerol and extraction time of 9 minutes and microwave power 300W for choline chloride:ethylene glycol.

flaxseed ; microwave ; natural deep eutectic solvents ; polyphenols ; ultrasound

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