Poly(3-hydroxybutyrate) production from thermally pretreated cheese whey by Stutzerimonas stutzeri BPSNITW100893:...

Poly(3-hydroxybutyrate) (P(3-HB)) is a biodegradable, biocompatible polyester widely recognized as a credible, environmentally friendly alternative to conventional plastics. However, its wider use is limited by high production costs, to which the carbon source contributes substantially. This study investigated P(3-HB) production from thermally pretreated cheese whey, a low-cost, high-strength dairy by-product, by Stutzerimonas stutzeri BPSNITW100893, a strain isolated from food waste collected at the National Institute of Technology Warangal. FTIR, ¹H NMR and GC-MS confirmed the characteristic chemical structure of P(3-HB), while XRD and HR-SEM indicated its semicrystalline nature and characteristic surface morphology; EDX confirmed the predominant carbon and oxygen composition of the recovered polymer; DLS analysis further indicated a hydrodynamic diameter of 148.66 nm for the dispersed polymer. Optimization of four factors using a rotatable central composite design (rCCD) located the optimum at a C/P ratio of 104.5 (w/w), a fermentation time of 51.8 h, an inoculum-to-substrate ratio of 7.02% (v/v) and a C/N ratio of 35.8 (w/w). Shake-flask validation experiments under these conditions yielded a P(3-HB) titre of 11.47 ± 0.64 g/L, a P(3-HB) content of 85.20 ± 2.06% (w/w) of dry cell weight (DCW), and biomass and P(3-HB) productivities of 0.2638 ± 0.009 and 0.2248 ± 0.010 g/L/h, respectively, with 83.8% lactose consumption and a P(3-HB) yield of 0.281 g/g lactose consumed. Compared with reported non-recombinant whey-utilizing microorganisms, the strain showed competitive volumetric productivity and polymer content, highlighting its potential for cheese whey valorization within a circular bioeconomy.