Enhanced Sugarcane Bagasse Conversion to Sugars by Ozonolysis and Liquid Hot Water Pretreatments

Cellulose hydrolysis is achieved by a complex multi-enzymatic system that works more effectively when hemicellulose, lignin and their derived compounds are decreased in lignocellulosic substrates. In order to achieve this, we studied a combined approach by combining ozonolysis with liquid hot water (LHW) pretreatment of sugarcane bagasse. Under these conditions there was a 100% increase in available cellulose accompanied by an 80% decrease in hemicellulose, and 40% of lignin was oxidized. The double-pretreated material was further hydrolyzed in 50mM Sodium Citrate buffer pH 5.0 at 10% (w/v) of solids loading using Cellic^® CTEC2 and HTEC2 (9.0 mg protein/ g glucan) at 50°C. HPLC analysis showed that more than 40 g/L of glucose was released after 96 hours of hydrolysis, reaching 59% of conversion of the glucan. Single pretreatments (ozonolysis and LHW) were also performed separately and both resulted gave 21 g/L of glucose, respectively. We showed that LHW pretreatment helps to remove partially the oxidized phenols after ozone attack, and also to solubilize the hemicellulose portion under high temperature, resulting in a more accessible glucan to the enzymes. The resultant liquor contains about 30 g/L of xylose and a large amount of phenolics (2.28 g/L of Gallic Acid Equivalent).  Conversion in the presence of this liquor is only 8% due to the strong inhibitory effect of phenols and carboxylic acids present in significant amounts in this fraction. Combining ozonolysis and LHW pretreatments is effective in separating cellulose from lignin and hemicellulose in bagasse, thereby generating fractions rich in sugars and phenolic compounds.