Effect of volumetric power input by aeration and agitation on pellet morphology and product formation of Aspergillus niger

The effect of the total volumetric power input under different aeration and agitation intensities on pellet morphology and glucoamylase production by Aspergillus niger AB1.13 was investigated in a 28 L stirred tank reactor. The pellet macro-morphology including pellet size and concentration was determined by the laser diffraction technique and digital image analysis. The pellet micro-morphology including pellet internal and surface structure was characterized by microscopic image analysis of pellet slices and sedimentation velocity measurements. The total volumetric power input, which comprises the volumetric power input by aeration and agitation, was kept constant for all cultivations, while the volumetric power input by aeration increased by the same degree as the volumetric power input by agitation decreased. Results revealed a notable variation in morphological data between pellets grown at different ratios of aeration to agitation, by which glucoamylase production yields were correspondingly altered. An increasing ratio of the volumetric power input by aeration resulted in a significant decrease in pellet size, a considerable increase in pellet concentration, a less compact surface structure of the pellets and a favorable production of glucoamylase.