15-15: Enzymatic hydrolysis of alkali-sulfite pretreated sugarcane hybrids containing reduced initial lignin contents

Alkaline pretreatment of lignocellulosic materials can increase cell wall porosity through delignification, breaking down some cross-linking, and causing swelling of microfibrils. Only partial hemicellulose removal and lignin re-localization are sufficient factors for increasing the digestibility of pretreated lignocellulose. With the advance of molecular biology and genetic engineering of plant species, lignin depleted plants become a reality. This advent is critical for cellulosic-ethanol production since only a modest pretreatment suffices to promote an efficient enzymatic digestion of the polysaccharides. Alkali-sulfite pretreatment of bagasse was used to compare the efficiency in terms of delignification and saccharification of sugarcane hybrids with different lignin contents. The effect of sulfite and NaOH charge on enzymatic digestibility of the bagasses pretreated at 121 ^oC for 2 h revealed that 5% of NaOH and 10% Na₂SO₃ produced the most feasible substrate for enzymatic conversion, reaching over 50% cellulose hydrolysis through 24 h. On the other hand, when the reagents were partially reduced, the enzymatic hydrolysis was less than 30%, indicating that the sulfite charge is essential to improve the enzymatic digestibility of sugarcane bagasse. Enzymatic hydrolysis of an experimental hybrid with lower initial lignin content (19.1%) reached 64% cellulose conversion after only 24 h of hydrolysis. This value was of the same order of magnitude as that obtained after 50 h of hydrolysis of the mill-processed bagasse. This work shows possible benefits for using samples with reduced initial lignin contents, showing that chemical loading in the pretreatment and hydrolysis time in the enzymatic step can be reduced.