Extracellular β-glucosidase production by the yeast Debaryomyces pseudopolymorphus UCLM-NS7A: optimization using response surface methodology

β-Glucosidase production by Debaryomyces pseudopolymorphus UCLM-NS7A using a simple nutrient medium containing cellobiose was evaluated under several biochemical and physiological parameters in submerged fermentation. Enzyme induction was also examined using different carbon and nitrogen sources. Cellobiose and ammonium nitrate were the best C and N sources to enhance β-glucosidase production. The addition of NaCl, MgSO 4, yeast extract, ethanol and Tween 80 to the nutrient medium before inoculation was also compared. A factorial design to optimize enzyme production was developed using four variables that most influenced β-glucosidase production and data analyzed by the response surface method. Optimal conditions to produce β-glucosidase in shake-flasks were 1.25% cellobiose, 0.05% Tween 80, 0.4% NH 4NO 3 over 72 hours. In another factorial design to further increase enzyme production, a lab fermenter using prior-determined shake-flask optimized conditions resulted in higher β-glucosidase titres at 72 hours, pH controlled at 6.25 and agitation of 200 rpm.