Isolation of Pure Lignin and Highly Digestible Cellulose from Defatted and Steam-Exploded Cynara cardunculus

In this work, a three-step approach to isolate the main components of lignocellulosic cardoon, lignin and cellulose, was investigated. The raw defatted biomass, Cynara cardunculus, after steam explosion was subjected to a mild organosolv treatment to extract soluble lignin (L1). Then, enzymatic hydrolysis was performed to achieve decomposition of the saccharidic portion into monosaccharides and isolate residual lignin (L2). The fractionation conditions were optimized to obtain a lignin as less degraded as possible and to maximize the yield of enzymatic hydrolysis. Furthermore, the effect of the use of aqueous ammonia as an extraction catalyst on both fractions was studied. Each fraction was characterized by advanced techniques, such as elemental analysis and 31P nuclear magnetic resonance (NMR), 13C–1H two-dimensional (2D)-NMR, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), and UV–vis spectroscopies for lignin and X-ray diffraction (XRD), Klason compositional analysis, elemental analysis, and ATR-FTIR spectroscopy for cellulose-rich fractions. The impact of the cellulose-rich fraction composition and crystallinity was also correlated to the efficiency of the hydrolysis step, performed using the enzymatic complex Cellic CTec3.