The researchers studied how different treatments affected the structure of two types of biomass, yellow poplar and empty fruit bunch. They used hydrothermal and oxalic acid pretreatments and found that the weight loss was slightly higher with oxalic acid. Yellow poplar had a higher weight loss and better enzymatic hydrolysis yield compared to empty fruit bunch. Hemicellulose was mostly removed during pretreatment, and the lignin of empty fruit bunch had more guaiacyl units and a lower S/G ratio. The lignin of empty fruit bunch also had a higher molecular weight and p-hydroxyphenyl unit after pretreatment. These changes in the biomass composition during pretreatment may affect the yield of enzymatic hydrolysis.