Effect of phenolic compounds derived from pretreated sugarcane bagasse on cellulolytic activities

Lignocellulosic residues, such as sugarcane bagasse (SCB), are a complex matrix composed by cellulose, hemicellulose and lignin that can be used for different biotechnological applications. These materials need to be pretreated to be accessible for enzymatic hydrolysis. Liquid hot water (LHW) pretreatment is an effective and cost-saving approach, since no catalyst is required, and an expensive reactor is avoided due to the low corrosive nature of this pretreatment. However, during the pretreatment phenolics derived from lignin are released, which are inhibitory of enzymes. Here, we evaluated the effect of phenolics compounds formed during the pretreatment of the SCB on cellulolytic activity. Two conditions for LHW pretreatment were used: 180 and 200º C for 30 min and two fractions were obtained: solid and liquid fractions enriched by cellulose/lignin and hemicellulose, respectively. The phenolics contained in the liquid and solid fractions were used for the experiments of enzymatic inhibition (cellulase and beta-glucosidase activities). The higher amount of phenolics (2.4 g/L) was observed in the liquid fraction of SCB pretreated at 200ºC/ 30 min. This condition also resulted in the highest inhibition of the enzymatic activity. Phenolics extracted from solid fraction (0.86 g/L) were shown to be more inhibitory than liquid for the beta-glucosidase activity. This work shows the importance of the optimization of the pretreatment process in relation to maximize the production of sugars and minimize the formation of inhibitory compounds to achieve the maximal efficiency of an enzyme hydrolysis-based process.