Fractionation of Broom (Cytisus striatus) Biomass Components via Mild Sulfite Pretreatment and Enzymatic Hydrolysis

The potential of broom biomass to produce oligo- and monosaccharides was investigated using mild sulfite pretreatment conditions followed by enzymatic hydrolysis. Both treatments were analyzed via response surface methodology using an experimental central composite rotatable design 2(4) + star, which explored the following variables: sulfuric acid charge (0% to 3%), sodium sulfite charge (0% to 4%, maximum temperature (150 degrees C to 190 degrees C), and time at maximum temperature (0 min to 30 min). Oligo- and monosaccharides in the pretreatment hydrolysates were determined using high performance liquid chromatography. The amount of total extracted xylose, mannose, and galactose ranged from 3.5% to 15.8% of the initial biomass, while the model estimated optimal reaction conditions enabled the extraction of practically all hemicellulose in the raw material. However, the mildest pretreatment reaction conditions, with low temperature and low sulfuric acid charges, provided a hydrolysate where a major part of the extracted polysaccharides remained in oligomer form, enabling their separation by filtration. The cellulose-rich solid residue was submitted to enzymatic hydrolysis using a Novozymes (R) enzymatic cocktail. The enzymatic hydrolysis was successful, but some polysaccharides remained in the solid residue, mainly composed of lignin. An enzymatic yield of 60% was attained with no added sulfite in the pretreatment at 190 degrees C, despite the confirmed positive role of sulfur content in the solid residues.

Automated summary

This study investigated the potential of broom biomass to produce oligo- and monosaccharides through mild sulfite pretreatment and enzymatic hydrolysis. Response surface methodology was used to optimize the extraction of hemicellulose and achieve a 60% enzymatic yield. The mildest pretreatment conditions allowed for the separation of polysaccharides in oligomer form, while enzymatic hydrolysis successfully extracted sugars from the cellulose-rich residue.