10-24: The importance of sulfonation in hydrolysis enzymatic of sugar cane bagasses with reduced lignin content

Bagasses, obtained from sugar cane hybrids with reduced lignin content, were submitted to loads of sodium hydroxide (2.5%, 3.75% and 5% m/m) and sodium sulfite (5%, 7.5% and 10% m/m) combined in a 1:2 ratio, exposed to 120°C/2h. Chemical composition and conductometric titrations of the pretreated bagasses were measured to characterize variations of the bagasses in different sulfite pretreated conditions. It was found that the greater the reactants concentration in the pretreatment, the more efficient the lignin and hemicelullose removal was therefore enabling enhancement of glucose yields based on the cellulose in the treated samples. Although lignin removal augments enzyme access to the substrate, this was not the only factor necessary to reach higher conversion rates. In this case, the effect of sulfonation was alsofavorable to cellulose conversions. The highest glucose yield was 92% from hybrid 58, which associated the effect of delignification (53.5%) with high sulfonic groups (0.6 mmol/g of lignin). The hemicellulose removal was only 20.4%. Comparatively, the amount of removed lignin from hybrid 58 after 5.0% sodium hydroxide and 2.5% sodium sulfite decreased to 33.6% and the variation of xylan proportion after sulfite pretreatments was the same as the decrease in lignin proportion. Moreover, little sulfonic group have been introduced during the pretreatment (0.27 mmol/g lignin). The fact that a greater proportion of OH^- ions was not beneficial to cellulose hydrolysis was attributed not only to the dissolubility of lignin, but also to the lower sulfonic groups, when compared to the same treatment utilizing 10% sulfite.