Pilot-plant production of protease by Alternaria tenuissima.

Agar slants of a selected Alternaria tenuissima strain were illuminated to give conidia suitable for further propagation. For production of protease with an optimal caseolytic activity in the region of pH 8 to 10, the fungus was cultivated in steel fermentors with 6- and 60-liter working capacity. Maximal activity, 1.5 enzyme units per liter, was attained in a medium based on liver after about 60 hr of cultivation. The protease was secreted parallel with, or slightly after, the main growth phase. The process could be run favorably with a relatively low aeration rate. The pH of the culture decreased during the process from 7.0 to about 6.3. This was the optimal region also when pH was kept constant by automatic pH control. Optimal temperature was about 28 C, which resulted in a maximal productivity of 0.057 enzyme units per liter per hr during the protease secretion phase. Replacement of the liver in the medium with skim milk, meat scrap, or rapeseed oil meal resulted in a decrease of the protease yield.