Extraction of chitin from white shrimp (Penaeus vannamei) shells using binary ionic liquid mixtures

Binary ionic liquid mixtures (IL) were used for the first time to extract chitin from shrimp shells. Two ionic liquids, 1-ethyl-3-methylimidazole acetate ([EMIM][Ac]) and 1-butyl-3-methylimidazole bromide salt ([BMIM][Br]), were mixed at ratios of 0:1, 1:1, 3:2, 4:1, and 1:0 and the properties of the IL and the characteristics of extracted chitin were investigated. With an increase in proportion of [EMIM][Ac], the viscosity, dielectric constant, and dielectric loss of IL gradually decreased (p < 0.05), whereas the conductivity, radius of gyration increased (p < 0.05). The best quality of chitin using IL (3:2) was achieved when the viscosity, conductivity, and radius of gyration were 0.16 ± 0.00 Pa‧s, 0.30 ± 0.01 S/m, and 0.10 ± 0.00 nm, respectively. The yield of chitin extraction using IL was 35.72 ± 0.31 %, and this was approximately 2.04 times higher than that using the acid-base method (17.50 ± 0.16 %). The Whiteness index (WI) of chitin extracted using IL (3:2) (94.93 ± 0.09) was better than commercial chitin (93.31 ± 0.11), and the secondary structure, surface morphology and thermal stability were similar to commercial chitin. Therefore, the binary ionic liquid mixture can be used as an effective green solvent to extract chitin from shrimp shells.