Production of semi-alkaline protease by Aspergillus niger

Aspergillus niger LCF no. 9 from a laboratory collection synthesized proteolytic enzymes active at semi-alkaline pH in high yield (90 PU casein/ml extract in 24 h). As these enzymes are inducible, the strain was grown on various protein-containing substrates, namely defatted soy, rapeseed, and sunflower cake, and ground lupin seeds. Soy cake proved best. Optimal fermentation conditions were defined and the process was extended to pilot scale. Since the proteases are highly unstable in the fermenting medium, rapid means of identifying the production optimum and of stopping breakdown of the enzymes were required: Detection of hydrolysis of benzoyl arginine paranitroanilide and injection of nitrogen provided a solution.