Substrate aggregation due to aerial hyphae during discontinuously mixed solid-state fermentation with Aspergillus...

Area of Science:

• Biotechnology
• Biochemical Engineering
• Industrial Microbiology

Background:

• Solid-state fermentation (SSF) is susceptible to process failures like channeling, often caused by evaporative cooling and the formation of interparticle mycelial networks.
• Effective mixing is essential in SSF to disrupt these mycelial networks and prevent process failure, ensuring consistent fermentation outcomes.

Purpose of the Study:

• This research aims to quantify and predict the impact of mycelial bonds on particle mixing dynamics in SSF, and conversely, how mixing affects mycelial growth.
• It represents the first attempt to establish a quantitative relationship between mycelial strength and mixing efficiency in SSF processes.

Main Methods:

• A novel experimental setup was designed to measure the tensile strength of aerial mycelium formed by Aspergillus oryzae cultivated between wheat-dough disks, using a texture analyzer.
• Tensile strength measurements were correlated with oxygen consumption data, enabling translation to a rotating drum fermentor setup for experiments with A. oryzae on wheat grain.
• Discontinuously mixed SSF experiments were conducted in a drum fermentor, measuring the number and size of grain aggregates post-mixing. Data were integrated into a 2D discrete-particle model.

Main Results:

• The discrete-particle model successfully predicted the quantity and size of grain aggregates remaining after the initial mixing event.
• The study demonstrated that the primary role of the first mixing action in SSF with A. oryzae is to break the mycelial network.
• This initial mixing is critical for preventing aggregate formation within the grain bed, rather than for water distribution or temperature gradient equalization.

Conclusions:

• The findings highlight the critical importance of mechanical disruption of mycelial networks in SSF.
• Initial mixing in Aspergillus oryzae SSF primarily serves to break hyphal bonds, thereby preventing aggregate formation and ensuring process stability.
• This understanding allows for improved process design and control in solid-state fermentation to mitigate common failure modes.