Strain selection and medium optimization for glucoamylase production from industrial potato waste by Aspergillus niger

BACKGROUND: Glucoamylase is one of the most common enzymes used in the food industry to break down starch into its monomers. Glucoamylase production and its activity are highly dependent on medium composition. Starch is well known as a glucoamylase inducer, and utilization of industrial starchy potato waste is an inexpensive way of improving glucoamylase production. Since glucoamylase production is highly dependent on medium composition, in this study medium optimization for glucoamylase production was considered to enhance glucoamylase activity. RESULTS: Among the evaluated microbial species, Aspergillus niger van Tieghem was found to be the best glucoamylase-producing fungus. The Plackett-Burman design was used to screen various medium ingredients, and malt extract, FeSO₄.7H₂O and CaCl₂·2H₂O were found to have significant effects on glucoamylase production. Finally, malt extract, FeSO₄.7H₂O and CaCl₂.2H₂O were optimized by using a central composite design of response surface methodology. The results showed that the optimal medium composition for A. niger van Tieghem was 50 g L^-1 industrial waste potato mash supplemented with 51.82 g L^-1 malt extract, 9.27 g L^-1 CaCl₂·2H₂O and 0.50 g L^-1 FeSO₄.7H₂O. CONCLUSION: At the end of optimization, glucoamylase activity and glucose production were improved 126% and 98% compared to only industrial waste potato mash basal medium; 274.4 U mL^-1 glucoamylase activity and 41.7 g L^-1 glucose levels were achieved, respectively.