An Effective Gluten Extraction Method Exploiting Pure Choline Chloride-Based Deep Eutectic Solvents (ChCl-DESs)

Gluten analysis is still affected by the lack of an efficient and universal extraction solvent for gliadin, i.e., the prolamine fraction of gluten which is the analytical target used to quantify gluten in food. In this investigation, the possibility of adopting pure choline chloride deep eutectic solvents (ChCl-DESs) as gliadin extraction media was tested. As prototypes of ChCl-DESs, ethaline and reline were chosen in view of their good dipolar and hydrogen bond donor (HBD) properties, as well as of their moderate enough viscosity. Their ability to act as effective solvents for gliadin and their inability to affect the subsequent gliadin detection by a frequently adopted and commercially available ELISA kit were first assessed. Ethaline and reline extraction performance was then tested by evaluating gliadin recoveries achieved on gluten-free food real samples before and after their spiking with controlled gliadin amounts. Higher recoveries were found by using these DESs in comparison with those gained by the usually adopted 60% (v/v) ethanol-water solvent. In fact, gluten recoveries ranging from 78 to 113%, with a RSD better than 13%, were achieved by using ethaline. Less good recoveries (from 67 to 132% with a RSD of 20%) were achieved with reline, even though they were however better than those found with 60% v/v ethanol-water solvent. These results make the proposed media profitable solvents for gliadin extraction and its subsequent detection by a commonly used immunoassay kit, without any change of the usual detection procedure.