Cooperative metabolism in mixed culture solid-state fermentation

Okara and brewer's spent grain (BSG) are manufacturing side streams that contribute significantly to food waste. In this study, solid-state fermentation (SSF) was performed using okara and BSG as substrates to investigate the effects of fermentation using pure and mixed cultures of Aspergillus oryzae and Bacillus subtilis. The total phenolic content (TPC), crude protein content, and total dietary fibre (TDF) of the fermented substrates were determined to evaluate their nutritional profiles. Okara fermented with a mixed culture under specific conditions produced the highest TPC values, and its TDF profile was the most ideal. These results reflected the presence of cooperative metabolism between Aspergillus oryzae and Bacillus subtilis which afforded greater enhancement in the nutritional profile of substrates compared to that of pure cultures. However, crude protein content could not be accurately determined, and more specific methods of protein quantification and optimisation of sample preparation for BSG in future work is recommended.