Abstract
BackgroundBiomass growth of Pencillium chrysogenum is characterised by a distinct pellet morphology consisting of compact hyphal agglomerates. Fungal pellets are advantageous in industrial process control due to rheological advantages but lead to biomass degradation due to diffusional limitations of oxygen and substrate in the pellet’s core. Several fermentation parameters are known to affect key pellet characteristics regarding morphology, viability and productivity. Pellet morphology and size are affected by agitation. Biomass viability and productivity are tightly interlinked with substrate uptake and dissolved oxygen concentration.ResultsThe goal of this study was to study the impact of the fermentation parameters power input, dissolved oxygen content and specific substrate uptake rate on morphology, biomass viability and productivity. A design of experiments (DoE) approach was conducted and corresponding responses were analysed using novel morphological descriptors analysed by a previously established flow cytometry method. Results clearly display inverse correlations between power input and pellet size, specific morphological parameters related to pellet density can be increased in direct proportion to power input. Biomass viability and productivity are negatively affected by high specific substrate uptake rates.ConclusionsBased upon multiple linear regression, it was possible to obtain an optimal design space for enhanced viability and productivity at beneficial morphological conditions. We could maintain a high number of pellets with favourable morphology at a power input of 1500 W/m3. A sound compromise between viability and high productivity is possible at a specific glucose uptake rate of 0.043 g/g/h at dissolved oxygen levels of 40% minimum.
Highlights
Cultivation strategies of filamentous fungi are characterized by specific fungal morphologies encompassing several forms ranging from homogeneously dispersed hyphae to dense agglomerates [22, 23]
In the following, results from multiple linear regression will be presented as a preliminary overview
A detailed discussion on the effects of factors power input (P/V), specific substrate uptake rate (qs) and dissolved oxygen content (dO2) on morphology, viability and productivity is available in the subsequent sections “Impact of power input on morphology”, “Impact of factors on viability” and “Interlink between productivity and specific substrate uptake”
Summary
Cultivation strategies of filamentous fungi are characterized by specific fungal morphologies encompassing several forms ranging from homogeneously dispersed hyphae to dense agglomerates [22, 23]. Industrial bioprocesses using Penicillium chrysogenum favour the sphere-like pellet form where tightly packed mycelium forms a dense core surrounded by a looser ‘hairy’ region [9]. These spherical pellets lead to advantages for process control such as lower viscosity of the cultivation broth as it contains less tangled mycelia [23]. Fungal pellets are advantageous in industrial process control due to rheological advantages but lead to biomass degradation due to diffusional limitations of oxygen and substrate in the pellet’s core. Biomass viability and productivity are tightly interlinked with substrate uptake and dissolved oxygen concentration
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