Pellet growth and citric acid yield of Aspergillus niger 110

Abstract

Inoculation methods and aeration conditions in the production of pellet cultures of Aspergillus niger 110 with acceptable citric acid yields were studied. Inoculating the fermentor with a preculture of pellets, instead of directly with spores, and carrying out fermentation at 1000 rev min −1 from seeding resulted in fungus growth in the form of compact, smooth pellets of uniform size and excretion of 48.0 g l −1 of citric acid. In contrast, cultivation of this same type of inoculum at 450 rev min −1 for the first 48 h, followed by 1000 rev min −1 for the remainder of the fermentation period, gave rise to different types of pellets of varying size that yielded only 30.3 g l −1 of citric acid. Under these latter aeration conditions, increasing the air flow from 0.9 to 1.3 vvm raised the citric acid yield to 48.7 g l −1 while leaving fungus morphology unaffected.