Effects of External Enzymes on the Fermentation of Soybean Hulls to Generate Lipids by Mortierella isabellina

Hydrolytic enzymes were evaluated on the lipid accumulation via an oleaginous fungal species, Mortierella isabellina, cultivated on sugars released from soybean hulls. The weight loss of soybean hull, fungal growth, and lipid production were tested under different loads of hydrolytic enzymes. M. isabellina could not directly utilize cellulose and adding cellulase and β-glucosidase significantly increased the cell growth and oil accumulation of M. isabellina on soybean hulls. The highest weight loss of soybean hulls was 47.80 % and the lipid production reached 0.14 g from 1 g of soybean hull when 12 U cellulase, 27.2 U β-glucosidase, 2,278.56 U pectinase, and 15 U hemicellulase were added. Fatty acids (76.82 %) accumulated in M. isabellina were C16 and C18, which are suitable for biodiesel production. These results provide a new application for soybean hulls to be applied as the raw material for the production of biodiesel fuel, besides its traditional role as animal feed supplements.