Valorisation of food waste through self-fermentation and photosynthetic bacterial protein production: efficiency, microbial dynamics and safety assessment

Abstract

Global food waste has become an important environmental challenge. In this study, we established a hierarchical valorisation system through ‘acidogenic fermentation–residue saccharification–photosynthetic bacteria (PSB) protein production’. Acidogenic self-fermentation for 72 h yielded liquid chemical oxygen demand (COD) and lactic acid levels of 56443.33 and 11634.64 mg/L, respectively. Solid-phase residues from the fermentation broth underwent enzymatic saccharification at 60 °C, yielding 68.7 % carbohydrate conversion and 16278 mg/L reducing sugar. The liquid phase was treated with PSB, which resulted in 95 %, 89.7 % and 66.6 % removal of lactic acid, COD and ammonium-nitrogen (NH₄⁺-N), respectively, and PSB biomass and protein of 1356.5 and 415.1 mg/g. The relative abundance of Rhodopseudomonas was 59.04 %, with a metabolic shift from carbohydrate utilization to amino acid synthesis. The enhanced expression of the genes Rubisco and GAPDH strengthened energy metabolism and promoted PSB growth. Safety assessments identified potential allergens in the PSB protein; however, in vitro digestibility reached 77.28 %. Heavy metal content was 85 %–97 % below the food safety limits, thus confirming the safety of the resulting protein.