Towards an holistic bioprocess to produce multifunctional bioingredients with Propionibacteriaceae

Microbial biomass is considered an alternative protein source that can contribute to ensure food security. Detrimentally, microbial growth processes can lead to the formation of CO2 and liquid effluent, which requires waste management. With the overall goal to contribute microbial solutions to address current societal challenges, the aim of this study was to establish a holistic bioprocess to deliver multipurpose bioingredients using food-grade Propionibacteriaceae. Strains of Propionibacterium freudenreichii, Acidipropionibacterium microaerophilum, Acidipropionibacterium acidipropionici, and Acidipropionibacterium olivae grew with glucose, glycerol, lactate, lactose, or lactose + glycerol in the presence of bicarbonate/CO2. The major fermentation metabolite was propionate with lower levels of acetate and succinate depending on strain and substrate. Based on pathway prediction, strains assimilated up to 10% mol CO2/mol glycerol while releasing up to 60% mol/mol with other substrates. Biomass contained 14%-44% protein and all essential amino acids depending on strain and growth condition. Fermentates conferred antimicrobial activity against bacteria and molds in broth dilution assays. In summary, different Propionibacteriaceae species showed potential for single cell protein and metabolite production for food-related application. We present an approach to design a bioprocess through a choice of culture, substrate, and suggest application possibilities of biomass and fermentates that avoid the generation of additional waste streams.