13-27: Soybean hulls as biomass for producing high-value products

Being a lignocellulosic material, soybean hulls contains cellulose (38-51%), that can be converted to ethanol. This biomass also contains from 9 to 14% of protein. Enzymatic hydrolysis of soybean with endoproteases may release oligopeptides with nutritional applications. Acid hydrolysis would decrease the hemicellulose contents of the material, turning the remaining insoluble cellulose more accessible to the hydrolytic enzymes. In this work, it was studied two approaches to produce ethanol and oligopeptides from soybean hulls. In the first one, the biomass was first submitted to hydrolysis using Novo-ProD, at 60°C, pH 9, for 8.3h, followed by acid hydrolysis with 3% H₂SO₄, solid/liquid ratio 1:4. The solid material was hydrolyzed with Acellerase 1500, at 50ºC, pH 4.8, and enzyme/substrate ratio of 20 FPIU/g of pretreated material. In the second approach, the biomass was only submitted to acid hydrolysis, followed by hydrolysis with cellullases and fermentation. After each pre-treatment, the liquid and solid fractions were chemically characterized. The proteolysis step allowed removal of 58.7% of protein. In the two routes, it was removed 46.7 % of hemicelluloses by the acid hydrolysis, which also remove almost all the protein of the hulls in the two routes. This result indicates the need of a previous proteolysis step if oligopeptides production is desired. The enzymatic conversion of cellulose in glucose was around the same, 39%, in the two cases. Nevertheless, the conversion of glucose in ethanol was higher when the biomass was only submitted to hydrolysis acid than when both enzymatic and acid hydrolysis occurred.