Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer synthesis by using 1-pentanol and oleic acid: Process optimization and polymer characterization

Effective high-level production of copolymer poly(3-hydroxybutyrate- co -3-hydroxyvalerate) P(3HB- co -3HV) is a necessary prerequisite for the application of this copolymer in large scale industries. In this study, batch culture of Cupriavidus malaysiensis sp. USMAA2-4 was investigated for the optimization of intracellular copolymer P(3HB- co -3HV). A central composite design (CCD) was used to optimize the growth [residual cell dry weight (RCDW)], PHA content, and 3HV monomer composition of the culture medium. The copolymer was optimized with respect to variation in time of incubation, varying concentration of 1-pentanol, aeration rate, and agitation speed. A maximum of 9.8 g/L RCDW with 250% increment and 8.7 g/L PHA concentration with 223% increment were obtained using the optimized conditions compared to 2.8 g/L RCDW and 2.7 g/L PHA concentration before optimization. Statistical optimization revealed that agitation speed and aeration rate established relatively major importance for the accumulation of this copolymer in a 3.6-L bioreactor. The productivity of the copolymer increased significantly by four-fold from 0.037 g/L/h to 0.160 g/L/h when the strain was cultivated under optimized conditions. However, the concentration of oleic acid and 1-pentanol remained the same before and after optimization proving the efficiency of statistical optimization in reducing the cost of polymer production. Optimization of copolymer not only decreased the production cost of P(3HB- co -3HV) but also helped in increasing productivity. The mechanical analysis revealed that tensile strength, elongation at break, and average molecular weight of the copolymer produced were 6–29 MPa, 1–3%, and 100–233 kDa, respectively.