Poly 3-hydroxybutyrate production from corncobs fortified with sugarcane molasses: optimization and recovery strategies.

Poly-3-hydroxybutyrate (PHB) production from agricultural waste offers a sustainable alternative to conventional plastics. This study optimized PHB production using B. licheniformis NA-cys8 on raw and pretreated corncobs supplemented with sugarcane molasses via solid-state fermentation. Optimal fermentation conditions were: pretreated corncobs (5 g) or raw corncobs (7.5 g), molasses (25 mL; 3.75 g total sugar), inoculum (4% v/v), temperature (37 °C), and incubation time (48 h). PHB yields from pretreated corncobs varied with pretreatment: 0.36 ± 0.018 g/L (15 mM aq. ammonia), 0.35 ± 0.018 g/L (0.6 N HCl), and 0.22 ± 0.007 g/L (0.2 N NaOH). Ammonia pretreatment gave the highest yield, while NaOH pretreatment resulted in the lowest despite achieving the highest cellulose enrichment (59.84%), likely due to inhibitory compound formation. Addition of PEG-4000 (2.5 mg/mL) significantly enhanced PHB production, yielding 1.09 ± 0.032 g/L from pretreated substrate (32.4% of dry cell weight) and 0.59 ± 0.030 g/L from raw substrate, representing 3.2-fold and 1.7-fold improvements over controls, respectively. Among extraction methods, chloroform gave the highest recovery: 0.76 ± 0.114 g/L (raw) and 1.15 ± 0.115 g/L (pretreated), followed by NaOCl (3% v/v) and H₂SO₄ (7.5% v/v). Pretreated substrates consistently yielded 1.5-1.7-fold higher PHB recovery across all extraction methods. This integrated study demonstrates successful valorization of corncobs and molasses for PHB production through optimized pretreatment, fermentation, stabilization, and recovery, offering a cost-effective approach within circular bioeconomy models.