Characterization of lignocellulose of Opuntia (Cactaceae) species using FTIR spectroscopy: possible candidates for renewable raw material

Opuntia is mainly cultivated for its fruit and cladodes, but the chemical composition of lignocellulose in this genus is unknown. The aims of this study were to quantify the extracts in different organic solvents and water, to quantify the lignocellulosic compounds, to compare the syringyl/guaiacyl ratio of lignin, and to calculate the crystallinity index of cellulose. The mature cladodes of three Opuntia species were dehydrated and milled; with the powder, sequential solvent extractions were performed based on TAPPI T-222 om-02 standard. Lignin Klason, cellulose, and hemicellulose were quantified. Fourier transform infrared spectra were obtained from cellulose and lignin samples to calculate the syringyl/guaiacyl ratio and the crystalline cellulose index. The percentages of water ranged from 89 to 92%; the Kruskal-Wallis analysis showed significant differences (p  < 0.05) in the extracts with ethanol/benzene, cellulose, and hemicelluloses. Opuntia ficus-indica had the highest amount of cellulose (32.6%) and hemicelluloses (9.8%). The syringyl/guaiacyl ratio was 1.59 to 2.12, due to the presence of 60% of syringyl. The crystallinity index revealed percentages higher than 60% of crystalline cellulose. The lignocellulosic percentages and the chemical composition of lignin and cellulose allow Opuntia species to be used in the production of cellulose nanofibers and biofuels.