Addition of Soybean Protein Improves Saccharification and Ethanol Production from Hydrothermally Pretreated Sugarcane Bagasse

The bioconversion yield of ethanol from lignocellulosic feedstocks is negatively affected by the unproductive adsorption of cellulolytic enzymes onto lignin. In this work, soybean protein was used as a lignin-blocking additive, with the aim of improving the production of ethanol from enzymatic hydrolysates of pretreated sugarcane bagasse. Investigation was made of the effects of the type of hydrothermal pretreatment process-steam explosion (SE) or liquid hot water (LHW), loadings of solids and enzymes, and bioreactor type. The addition of soybean protein led to a exceptional 76% increase of glucose released using the LHW pretreated bagasse, after 24 h of reaction, employing a high-solids loading (15%, w/v) and a low enzyme dosage (5 FPU/g dry biomass). A significant improvement was also achieved for industrial-like mixing conditions in a bench-scale stirred tank reactor, increasing the glucose released by 61 and 42% for the LHW and SE processes, respectively. Ethanol production was also positively affected by the presence of soybean protein, with increases of up to 86 and 65% for the LHW and SE hydrolysates, compared to the control experiment. Characterization of the sugarcane bagasse after the adsorption of soybean protein, using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), corroborated the higher affinity of the additive for the LHW bagasse. These findings suggest that soybean protein supplementation during enzymatic hydrolysis by commercially available enzymes is an effective strategy for achieving higher saccharification yields from hydrothermally pretreated biomass, hence improving ethanol production.