Optimized Bioconversion of Cheese Whey to Poly(Hydroxybutyrate) (PHB) by Mangrove-Isolated Bacillus Cereus

Poly(hydroxybutyrate) (PHB) is a biodegradable and biocompatible polyesters synthesized by bacteria for carbon and energy storage. Given its mechanical properties comparable to those of polypropylene, PHB represents a viable alternative for reducing conventional plastic pollution. However, the high production costs associated with traditional carbon sources, such as glucose, remain a significant barrier to large-scale PHB. In this study, an alternative carbon source derived from the interaction between whey and demerara sugar was evaluated for the optimization of PHB production by mangrove- isolated bacteria. The Central Composite Design data indicated that whey concentration at its upper axial point (39.99 mL∙L⁻¹), and demerara sugar at its central point (20 g∙L⁻¹) as the most favorable conditions for PHB production. Fermentation experiments utilizing this combination for 48 h with an isolate identified as Bacillus cereus, resulted in the highest cell biomass production of 2.9 g∙L⁻¹, and a polymer recovery rate of 67.39%, corresponding to 2 g∙L⁻¹. The characterization of purified polymer using FTIR, DSC, TGA/DTG, SEM and GC-MS confirmed the biopolymer as poly(hydroxybutyrate) (PHB). These findings provide information on efficient fermentation parameters using whey as strategies of conversion into bioplastics and highlight the potential of B. cereus isolated from mangroves for future industrial-scale production.