Production of cellooligosaccharides from oil palm bunch in bio-based choline chloride deep eutectic solvents and MALDI-TOF MS analysis of COS mixture

Lignocellulosic biomass pretreatment and cellulose dissolution are principal challenges for its conversion to high-value chemicals, materials and fuels. This work focused on production of soluble cellooligosaccharides (COS) from palm bunch for future use as nutraceutical supplement to enhance human's immune and digestive systems. Deep eutectic solvents (DESs) have been found as eco-friendly, renewable and promising solvents selective for lignin and hemicellulose removal from biomass. Additionally, the investigation of most suitable DES for both cellulose dissolution and subsequently cleavage of cellulose to COS is crucial. In the study, palm empty fruit bunch (EFB) was pretreated in different DES for screening of most favorable cellulose inter- and intra-molecular structural dissolution in a combination with beta,1–4 glycosidic bond cleavage by elevated reaction temperature for COS production. ChCl/urea was found to be the most promising DES for dissolving 76.83% of EFB constituents. The highest COS production yield at 90.1%w/w based on treated EFB fraction (74.7% COS yield based on cellulose in native EFB) was achieved in ChCl/urea DES from cellulose fraction extracted from EFB at 240 °C for 20 min. The study additionally provided insightful characterization and elucidation of COS molecular structure using 2D-HSQC and MALDI-TOF/MS techniques. MALDI-TOF/MS was a promising and rapid technique for simultaneously qualitative and quantitative analysis of COS at different degrees of polymerization in COS product.