Influence of Rheological Behavior on Oxygen Transfer and Energetic Efficiency in Pestalotiopsis microspora Cultures

High-value metabolites, such as antibiotics and enzymes, are primarily produced using filamentous fungi. However, their morphological complexity increases broth viscosity during biomass growth, hindering industrial scale-up by impairing both power input and mass transfer. The interaction between biomass growth, rheology, power input, and oxygen transfer is first addressed here by evaluating mycelial rheology and determining the volumetric mass transfer coefficient (kLa) (dynamic method) and oxygen uptake rate (respirometry) across different operating conditions. These confirmed that the mycelial broth’s pseudoplastic behavior significantly influences volumetric power input and kLa correlations. However, specific power input analysis revealed that operating at higher stirring rates (800 rpm) at higher cell-density cultures is 28.17% more energetically efficient than at low speeds (500 rpm). Furthermore, the oxygen supply-to-demand ratio, calculated via Excel model-fitting, allowed for the estimation of “metabolic power input” which represents the required energy to fit oxygen demand. Results also reveal that at 3.67 ± 0.34 g L−1 of biomass effectively channel up to 51% of total energy toward aerobic metabolism, compared to only 17–30% for 0.73 ± 0.01 g L−1 of biomass. These findings show that volumetric power inputs around 4 kW m−3 improve oxygen transfer efficiency, even at relatively high biomass concentrations.