Sustainable PHAs production by Cupriavidus necator DSM 545 from whey permeate

Polyhydroxyalkanoates (PHAs) have emerged as promising biodegradable polymers with the potential to replace fossil plastics. Their widespread adoption is impeded by economic constraints, particularly the high cost of carbon substrates for microbial fermentation. Whey permeate, by-product of cheese production and of whey membrane filtration processes, comprises lactose, minerals, and other soluble components separated from milk during cheese whey processing. Cupriavidus necator, one of the most used strain for PHAs has garnered attention for its biopolymer accumulation proficiencies. However, its non-capability to use lactose as a carbon source, poses a significant challenge to maximizing PHA yields from dairy residues. In this study, the enzymatic hydrolysis of lactose into glucose and galactose has been obtained using Maxilact® LGI 5000, an industrial formulation containing β-galactosidase. Once identified the optimal conditions for the use of Maxilact® LGI 5000, the growth of C. necator DSM 545 was then evaluated in flasks containing MM medium amended with enzymatically treated permeate (containing lactose 20 g/L), glucose (10 g/L) and a mixture of glucose (10 g/L) and galactose (10 g/L) as a carbon source. No differences in terms of biomass and accumulated PHAs were observed when pure sugars or the mixture of glucose and galactose were present in the medium. Furthermore, in hydrolyzed permeate, biomass and accumulated PHAs was 5.63 g/L and 56,24 % of CDW, respectively, higher than in pure sugar (5.07 g/L and 52,43 %). In addition, experiments in SSF (Simultaneous Saccharification and Fermentation) mode were also conducted offering a streamlined approach to bioconversion. The accumulated PHAS and biomass in SSF mode, were similar to those obtained with enzymatically hydrolized permeate in terms of biomass and PHAs accumulation.