Raman spectroscopy measurements of glucose and xylose in hydrolysate: Role of corn stover pretreatment and enzyme composition

The effect of corn stover pretreatment on glucose quantitation in hydrolysate using Raman spectroscopy is evaluated. Dilute sulfuric-acid pretreatment results in a 20 mg mL−1 glucose limit of detection in hydrolysate. Soaking in aqueous ammonia pretreatment produces a 4 mg mL−1 limit of detection. Water, ethanol or hexane extraction of corn stover reduces the spectral background that limits glucose detection in dilute acid hydrolysate. Additionally, a Raman spectroscopy multi-peak fitting method is presented to simultaneously measure glucose and xylose concentration in hydrolysate. This method yields a 6.1% average relative standard error at total saccharide concentrations above 45 mg mL−1. When only cellulase is present, glucose and xylose yield were measured by Raman spectroscopy to be 32 ± 4 and 7.0 ± 0.8 mg mL−1, respectively. When both cellulase and hemicellulase were present, xylose yield increased to 18.0 ± 0.5 mg mL−1. Enzymatic or colorimetric assays confirmed the validity of the Raman spectroscopy results.