Bioconversion of bread waste into high-quality proteins and biopolymers by fermentation of archaea Haloferax mediterranei

The valorization of bread waste into high-quality protein and biopolymers using the halophilic microorganism <i>Haloferax mediterranei</i> presents a sustainable approach to food waste management and resource optimization. This study successfully coproduced protein and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) biopolymer with a biomass content of 8.0 ± 0.1 g L^-1 and a productivity of 11.1 mg L^-1 h^-1. The fermentation process employed 3.0% w/v of enzymatically hydrolyzed bread waste. The amino acid profile of the cell biomass revealed a total content of 358 g kg^-1 of biomass dry weight (DW), including 147 g kg^-1 DW of essential amino acids. The protein quality, assessed through <i>in-vitro</i> enzyme digestion, indicated a high-quality protein with a digestibility value of 0.91 and a protein digestibility-corrected amino acid score (PDCAAS) of 0.78. The PHBV biopolymer component (36.0 ± 6.3% w/w) consisted of a copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate in a 91:9 mol% ratio. This bioconversion process not only mitigates food waste but also generates valuable biomaterials.