D fructose

For NADES preparation, chemicals choline chloride, 1,2-propanediol, DL-malic acid, malonic acid, D-sorbitol, urea (all Thermo Fisher Scientific, Waltham, MA, USA), citric acid monohydrate, glycerol, D(−)-fructose (all Carl Roth, Karlsruhe, Germany), D(+)-glucose (Merck, Darmstadt, Germany) and methylurea (Acros Organics, Geel, Belgium) were used. Methylurea had a specified purity of 97%, and all other reagents were at least 98% or higher. In HPLC mobile phases, ultrapure water prepared from deionized water with a Barnstead MicroPure system (Thermo Fisher Scientific, Waltham, MA, USA), HPLC-grade acetonitrile (VWR, Radnor, PA, USA) and formic acid (Honeywell, Charlotte, NC, USA) were used. The solvent for NMR analyses was chloroform-d₁ (VWR). Other solvents used in this study were partly denatured ethanol (96% v/v, AustrAlco, Spillern, Austria) methanol (≥99.9%, Carl Roth) and dichloromethane (≥99.5%, Carl Roth). Reference substance spilanthol was isolated in the course of this work with a purity of 97% as determined by NMR.

Double-deionized water (Nanopure^®, Werner GmbH, Leverkusen, Germany) was used. Ethanol (HPLC grade) and acetic acid (LC-MS grade) were purchased from Fisher Scientific (Loughborough, UK). Acetonitrile (HPLC and LC-MS grade) was obtained from Honeywell Specialty Chemicals (Seelze, Germany). Formic acid (HPLC grade) and lactic acid (90%) were purchased from VWR Int. S.A.S (Darmstadt, Germany). For NADES preparations, betaine (98%) and urea (99.5%) were purchased from Fisher Scientific (Loughborough, UK). D-Fructose (99%) and D-glucose (99%) were obtained from Carl Roth (Karlsruhe, Germany). Amberlite^®XAD-16N, choline chloride (>98%), and 1,2-propanediol (99%) were purchased from Sigma-Aldrich (Deisenhofen, Germany). Trans-resveratrol standard (>98%) was obtained from Carl Roth (Karlsruhe, Germany), and trans-ε-viniferin (>94%, λ 280 nm, in-house method, [35 (link)]) was isolated from the commercial product Vineatrol^®30 (Breko GmbH, Bremen, Germany). Stilbenoid tetramers r-2-viniferin (95%, λ 280 nm) and r-viniferin (91%, λ 280 nm) were isolated from de-colored Vitisin^® Powder (Actichem, Montauban, France) using an in-house method [46 ]. Each sample for UHPLC and LC-MS analysis was filtered through 0.2 µm PTFE syringe filters from Agilent Technologies (Waldbronn, Germany).