Biowaste upcycling into second-generation microbial protein through mixed-culture fermentation.

Securing a sustainable protein supply at the global level is among the greatest challenges currently faced by humanity. Alternative protein sources, such as second-generation microbial protein (MP), could give rise to innovative circular bioeconomy practices, synthesizing high-value bioproducts through the recovery and upcycling of resources from overabundant biowastes and residues. Within such a multi-feedstock biorefinery scenario, the wide range of microbial pathways and networks that characterize mixed microbial cultures, offers interesting and not yet fully explored advantages over conventional monoculture-based processes. In this review, we combine a comprehensive analysis of waste recovery platforms for second-generation MP production with a critical evaluation of the research gaps and potentials offered by mixed culture-based MP fermentation processes. A critical overview of second-generation microbial protein (MP) biorefineries as a means to upcycle overabundant organic waste and residues through relevant mixed-culture fermentation platforms is provided. Naturally enriched mixed cultures and synthetically engineered co-cultures can contribute to improve the process performances of microbial fermentation as well as the final product specifications. The multiproduct application potential of MP is expanding rapidly, moving beyond nutritional applications to include new added-value bioproducts, such as slow-release fertilizers and protein-based bioplastics. The techno-economic feasibility of the conversion platforms, the stability/quality of the mixed-cultures, and the regulatory acceptance of products obtained from waste/residues call for further investigation. [ABSTRACT FROM AUTHOR]