Isolation and Utilization of Fungal Chitin

Chitin is a biopolymer found in nature. It has attracted much interest due to its many uses in various sectors, including biotechnology, agriculture, food, and medicine. Traditionally sourced from crustacean exoskeletons, chitin extraction poses some challenges due to its contamination with allergenic protein and its reliance on harsh chemical treatment during extraction. Compared to chitin obtained from crustaceans, fungal chitin has recently become a viable substitute, providing several benefits, such as being plant-based and free of allergens. It does not vary with the seasons or regions. However, the purification of chitin from fungal biomass is often challenging, as it is often contaminated with other cellular components such as glucans, proteins, lipids, and nucleic acids. Because glucans and chitin have similar structures, removing glucans is more challenging than removing other components. Consequently, when chitin is extracted from mushrooms, the presence of branched 1,3/1,6-β-D-glucans leads to Chitin Glucan Complex (CGC) isolation rather than isolation of purified chitin polymer. Some studies indeed demonstrated methods for fungal chitin extraction, but the purity and characteristics of the extracted chitin remain unclear due to insufficient characterization. The goal of the reported work is to investigate the chitin extraction from three different mushrooms- (white (Agaricus bisporus), Shiitake (Lentinus edodes), and oyster (Pleurotus ostreatus) using four different methods: 1. traditional pulping (using NaOH), 2. extraction with 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc] ionic liquid (IL), 3. pulping with 1-butyl-3-methylimidazolium hydrogen sulfate IL ([C4mim][HSO4], and 4. pulping using deep eutectic solvent system (DES) made of choline chloride and lactic acid, ([Cho]Cl : Lactic acid = 1:2 mol/mol). A further focus will be on the characterization of this polymer to identify different properties by several characterization techniques including Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (pXRD), thermogravimetric analysis (TGA), degree of acetylation (%DA) measurements, carbon-13 nuclear magnetic resonance (13C NMR) spectroscopy, and purity assessment. Finally, fibers and hydrogels were prepared from the isolated materials to determine whether complete separating the chitin and glucans is required or whether the chitin somewhat contaminated with glucans can be used directly for material preparation. Scanning electron microscopy (SEM) and tensile testing were used to characterize the prepared materials. The yield and characterization following the extraction procedure confirmed purer chitin when treated with NaOH for 24 h. At the same time, DES was deemed unsuitable for the intended use, and the ionic liquids were shown to be moderately effective. The purest isolated chitin was used for materials preparation. The molecular weight (Mw) of the isolated polymer allowed it to be fabricated into hydrogels and fibers.