Optimizing Gluten Extraction Using Eco-friendly Imidazolium-Based Ionic Liquids: Exploring the Impact of Cation Side Chains and Anions

Gluten is a well-known food allergen globally, and it can induce immune responses in celiac- and nonceliac gluten-sensitive patients. The gliadin proteins from gluten have a special amino acid sequence that make it hydrophobic. One way to deal with gluten allergies is to provide a gluten-free diet. The hydrophobic characteristic of gliadin makes gliadin detection more difficult. An analyst needs to use an organic solvent or multiple processes to denature gluten for extraction. Although organic solvents can rapidly extract gluten in a sample, organic solvent also denatures the antibody and induces false biotest results without buffer dilute, and the accuracy will reduce with buffer dilute. An ionic liquid (IL) is a highly modifiable green chemical organic salt. The imidazolium has a cationic structure and is modified with different lengths (C = 0, 1, 3, 5, 7, 9, and 12) of carbon side chains with organic and inorganic anions [methanesulfonate (MSO), Cl-, F-, NO3-, HSO4-, and H2PO4-] to make different kinds of ILs for testing the solubility of gliadin. Different IL/water ratios were used to test the solubility of gluten. We measured the solubility of gliadin in different imidazolium ILs, and the kinetic curve of gliadin dissolved in 1% [C5DMIM][MSO](aq) was conducted. We also used circular dichroism spectroscopy and an enzyme-linked immunosorbent assay to measure the gliadin structure and the effect of binding with an antibody after 1% [C5DMIM][MSO](aq) treatment. An 2,3-bis-(2-methoxy-4- nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay was used to test the toxicity of [C5DMIM][MSO](aq) in N2a cells. In our research, 1% [C5DMIM][MSO](aq) produced a good solubility of gluten, and it could dissolve more than 3000 ppm of gluten in 5 min. [C5DMIM][MSO](aq) did not break down the gluten structure and did not restrict antibody binding to gluten, and more importantly, [C5DMIM][MSO] did not exhibit cell toxicity. In this report, we showed that [C5DMIM][MSO] could be a good extraction solution applied for gluten detection.