Rutin extraction from Tartary buckwheat and extraction mechanisms using surface-active ionic liquids with different cations and anions

Abstract

Surface-active ionic liquids (SAILs) are a new class of ILs that can enable green extraction processes. This study examined the extraction effect of nine SAILs in ultrasonic extraction of rutin from Tartary buckwheat flour. They were composed of different amino acid or fatty acid anions and 1-octyl-3-methylimidazolium ([C₈mim]), 1-ethyl-3-methylimidazolium ([C₂mim]), or cholinium cations ([Cho]), exhibiting diverse hydrophobicity (log P), pH, and critical micelle concentration (CMC) values. The main extraction conditions used were: SAIL concentration 100 mM, solid-liquid ratio 1:30 (g/mL), temperature 50 °C, and extraction duration 45 min. Among them, cholinium myristate ([Cho][Myr]) exhibited the highest extraction efficiency about 14 mg/g, comparable to that using 80% aqueous methanol. Partial least squares regression (PLSR) analysis showed strong correlations between extraction efficiency and log P, CMC and pH of the SAILs, and their medium values yielding the best extraction performance of [Cho][Myr]. TEM and SEM measurements confirmed micellar extraction was enabled by the SAILs. HPLC analysis demonstrated enhanced rutin solubility in SAIL micellar solutions. UV–Vis and ¹H NMR analyses indicated that rutin was solubilized in outer cores of SAIL micelles, due to electrostatic and hydrogen bonding interactions between rutin phenolic –OH groups and SAIL imidazolium or cholinium cations as well as amino or carboxyl groups of anions. Chemical calculations showed that [Myr]-rutin had a lower binding energy (− 52.54 kJ/mol) than [C₈mim]-rutin (− 39.33 kJ/mol), which may be a reason for the better extractability of the fatty acid-based SAILs than amino acid-based SAILs. This work can provide guidance for efficient and green extraction of rutin from natural products and how to select and optimize SAIL structures for such applications.