Production of the renewable bioplastic poly-3-hydroxybutyrate from underutilized dairy waste streams through...

Whey waste streams from dairy processing can present major challenges for the industry in terms of their further utilization and the environmental impact of disposal. However, these waste streams generally contain high concentrations of nutrients with the potential to act as substrates in bioprocesses to generate sustainable high-value products. In this work, we evaluated the use of salty whey (SW) and acid casein whey (ACW) as feedstocks for the microbial production of poly-3-hydroxybutyric acid (PHB), a renewable and biodegradable bioplastic. Five PHB-producing strains-Priestia megaterium DSM32, Cupriavidus necator DSM545, Azohydromonas lata DSM1123, Paraburkholderia fungorum DSM1749, and Halomonas halophila DSM4770-were examined for growth and PHB production in ACW and SW. Compared with the control minimal salts medium, both whey types supported higher biomass yield, with SW generally producing more biomass than ACW. In small-scale (50 mL) batch fermentations in SW, H. halophila DSM4770 produced the highest yield of PHB (1.06 g/L), whereas C. necator DSM545 achieved the highest yield in ACW (0.34 g/L). These 2 substrate-strain combinations were selected for scale-up to 500-mL batch fermentations. At this scale, PHB yields reached 0.30 g/L for C. necator DSM545 in ACW but only 0.34 g/L for H. halophila DSM4770 in SW. Although PHB production from SW has been reported previously, this study is the first to demonstrate PHB production using ACW. These findings highlight the potential of SW and ACW as viable feedstocks for the microbial production of PHB, contributing to the valorization of dairy waste streams.