Sustainable Polyhydroxyalkanoates production by Cupriavidus necator DSM 545 from whey permeate

Polyhydroxyalkanoates (PHAs) are biodegradable biopolymers with the potential to replace fossil-based plastics. However, their widespread adoption is currently limited by the high cost of carbon substrates. Whey permeate is rich in lactose and minerals and thus represents a potential sustainable carbon source. Cupriavidus necator is commonly used for PHAs production; however, its inability to utilize lactose significantly limits PHAs yields from dairy residues. In this study, lactose from permeate was enzymatically hydrolyzed into glucose and galactose using Maxilact® LGI 5000, an industrial β-galactosidase formulation. After determining the optimal conditions for the use of Maxilact® LGI 5000, the growth of C. necator DSM 545 was evaluated in minimal medium supplemented with enzymatically treated whey permeate. In the hydrolyzed permeate, the biomass and accumulated PHAs reached values above 5 g/L and around 60 % of cell dry weight (CDW), respectively, comparable or even higher than the yields obtained in the benchmark experiment with pure sugars. A Simultaneous Saccharification and Fermentation (SSF) setup was also adopted and provided a more streamlined approach to bioconversion. In conclusion, although further optimization of the process conditions is necessary, these results indicate that the use of whey permeate combined with β-galactosidase can greatly enhance PHAs production.