Rational feeding strategies of substrate and enzymes to enzymatic hydrolysis bioreactors

Abstract

Bioreactors operating in fed-batch mode improve the enzymatic hydrolysis productivity at high biomass loadings. The present work aimed to apply rational feeding strategies of substrates (pretreated sugarcane straw) and enzymes (CellicCtec2?) to achieve sugar titers at industrial levels. The instantaneous substrate concentration was kept constant at 5 % (w/v) along the fed-batch, and the enzyme dosage inside the bioreactor was adjusted so that the reaction rate was not less than a pre-defined value (a percentage of the initial reaction rate - rmin). When r reached values below rmin, enzyme pulses were applied to return the reaction rate to its initial value (r0). The optimized feeding policy indicated a reaction rate maintained at a minimum of 70 % of r0, based on the trade-off between glucose productivity and enzyme saving. Initially, it was possible to process a total of 21 % (w/v) solid load, achieving 160 g/L of glucose concentration and 80 % of glucose yield. It was verified that non-productive enzyme adsorption was the main reason for some reduction of hydrolysis yield regarding the theoretical cellulose-to-glucose conversion. An increment of 30 g/L in the final glucose concentration was achieved when a lignin-blocking additive (soybean protein) was used in the enzymatic hydrolysis.