Valorization of oilseed residues: Extraction of polyphenols from flaxseed hulls by pulsed electric fields

• Pulsed electric fields are applied on flaxseed hulls for polyphenols extraction.
• The effects of the energy input, electric field strength, solvent composition and rehydration time are studied.
• There exist optimal operating parameters for polyphenols extraction.
• The alkaline hydrolysis allowed improving the release of polyphenols.

This work aims at obtaining extracts with high level of polyphenols from flaxseed hulls treated by pulsed electric fields (PEF). The effect of the different operating parameters was studied on the extraction of polyphenols such as the PEF treatment duration, the PEF electric field strength, the solvent composition (ethanol, acid or base content) and the rehydration duration of the product. Results have shown that a PEF treatment allowed the extraction of up to 80% of polyphenols when applied at 20 kV/cm for 10 ms. For lower PEF electric field strength, the extraction efficiency was smaller. The rehydration of the product before PEF application improved the treatment efficiency. The highest polyphenols increase (≈37%) was observed when the product was rehydrated for 40 min before PEF application. The addition of ethanol, citric acid and sodium hydroxide has increased the extraction of polyphenols. The highest polyphenols yield was reached with a solvent containing 20% of ethanol and 0.3 mol/L hydroxide sodium. The alkaline hydrolysis was more effective than the acidic hydrolysis.