Production of a fungal aspartic protease via solid-state fermentation using a rotating drum bioreactor

BACKGROUND

Solid-state fermentation (SSF) has gained attention recently as a promising approach for producing a range of high-value industrial products. SSF has several benefits, including a high product yield, a lesser chance of contamination, a resemblance to some fungi and bacteria's native environment, a lower energy need, and cost-effectiveness. Additionally, the enzyme extraction from concentrated solutions facilitates the recovery procedure. Mucor racemosus, a filamentous fungus, has the potential to produce a milk-clotting enzyme (aspartic protease) cultivated on various combinations of the solid media to investigate the effect of media on the production and activity of the milk-clotting enzyme.

RESULTS

The fermentation was scaled up by utilizing Terrafors-IS Infors HT in-situ sterilizable rotating solid-state bioreactor to cultivate the fungus. The effect of agitation (rotation on the day of inoculation and day 1), aeration (air flow rates of 1 L and 2 L/min), and moisture content (60% and 90%), during SSF were investigated. The profiles of various operational parameters (that is, temperature, pressure, flow rate, exit O₂, and exit CO₂) were monitored using the provided software, and data were collected at 10-min intervals during the whole course of fermentation. The results suggest that aeration has a remarkable effect on the quantity of biomass produced, but it doesn't assure high enzyme production. The highest milk clotting activity of ~570 U/mL was recorded with a moisture content of 60% and a flow rate of 1 L/min.

CONCLUSION

A high yield of ~570 U/mL of the enzyme with desired characteristics was obtained with minimum moisture availability at low temperatures. The results narrated in this study validate the SSF process for producing aspartic protease from wheat bran using a rotating solid-state bioreactor to be used as a potential milk coagulant in the cheese industry. © 2024 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).