Effects of pellet morphology on broth rheology in fermentations of Aspergillus terreus

• Published in: Biochemical engineering journal 2005-11, Vol.26 (2), p.139-144
• Main Authors: Rodríguez Porcel, E.M., Casas López, J.L., Sánchez Pérez, J.A., Fernández Sevilla, J.M., Chisti, Y.
• Format: Article
• Language: English
• Subjects: Agitation; Aspergillus terreus; Biological and medical sciences; Biotechnology; Filamentous fungi; Fluidized bed bioreactors; Fundamental and applied biological sciences. Psychology; Pellet morphology; Rheology
• ISSN: 1369-703X; 1873-295X
• DOI: 10.1016/j.bej.2005.04.011

Effects of pellet morphology on broth rheology are reported for pelleted submerged cultures of the lovastatin producing filamentous fungus Aspergillus terreus, growing in fluidized bed and stirred tank bioreactors. The pellet diameter and compactness were affected by the agitation intensity of the broth; however, the total biomass productivity was not affected. In fluidized beds and stirred tanks with agitation intensity of up to 300 rpm (impeller tip speed of 1.02 m s −1), the fungal pellets were stable at diameters of up to about 2300 μm. In more intensely agitated stirred tanks (≥600 rpm; impeller tip speed of ≥2.03 m s −1), the stable pellet size was only about ≤900 μm. The biomass concentration and the pellet diameter were the main factors that influenced the flow index and the consistency index of the power-law broths. Because the biomass productivity was the same in all experiments in a given type of reactor and the oxygen concentration was kept at ∼400% of air saturation, the pellet size and morphology were not influenced by oxygen mass transfer effects. Pellets were always dense in the core region and no necrosis of the biomass occurred.