Bioconversion of whey to Polyhydroxyalkanoate (PHA): Process Optimization and Yield Enhancement

Polyhydroxyalkanoate (PHA) is a biodegradable biopolymer with significant potential as an eco-friendly substitute for conventional plastics. This study investigates microbial bio-transformation and enhanced biosynthesis of polyhydroxyalkanoate (PHA) using cheese whey (a dairy industry processing waste) as a substrate. The process employs Stutzerimonas stutzeri BPSNITW100893, a novel strain isolated from food waste generated at the Institute Food Court-C of NIT Warangal, which produces higher PHA, compared to six isolated strains from initial screening using mineral salt media (MSM) and characterized using FTIR and NMR. A rotatable Central Composite Design (rCCD) based optimization using four key factors remarkably enhanced production under optimal physiological conditions, i.e., C/P ratio (147.6 w/w), fermentation time (69.6 hours), inoculum to substrate ratio 8.83 (v/v) %, C/N ratio 45.9 (w/w). A high PHA mass fraction yield % of 66.51% was observed as compared to the predicted yield of 56.48% from cheese whey hydrolysate as feed. Scale-up studies were successfully conducted up to 3 L with optimized parameters confirmed by cell proliferation studies. These studies demonstrated high productivity with a maximum PHA mole fraction yield of 73.03 ± 4.92% and a productivity rate of 1.319 ± 0.089 g/L/h, highlighting the potential of dairy processing waste as a substrate for sustainable biopolymer production and waste valorization.