Poly(3-hydroxybutyrate) production from cassava processing wastes by Paracoccus sp. through high cell density cultivation: Effects of substrates limitation and kinetic analysis

Abstract

Polyhydroxybutyrate (PHB) is bioplastic that has been recognized as a viable alternative to petroleum-based ones, owing to its biodegradability and biocompatibility. However, its use has long been hampered by its high selling price, caused mainly by using costly fermentation feedstock. In the present study, cassava pulp (CP) was investigated as an alternative low-cost carbon source for a high cell density cultivation of Paracoccus sp. KKU01 for PHB production. CP was hydrolyzed enzymatically, and the resulting hydrolysate was used as the base medium to optimize the bacterial growth conditions, i.e., medium compositions and dissolved oxygen setpoints, attaining as high as 40.9 ± 0.0 g/L of biomass. The optimum growth conditions were subsequently used in 4 fed-batch fermentation regimes, and Regime 2, where complete medium (CP hydrolysate supplemented with other nutrients) was fed twice followed by twice feedings of concentrated CP hydrolysate (CPH), was found to give highest biomass and PHB production of 114.5 ± 1.3 and 47.8 ± 3.9 g/L, respectively, with 41.8 ± 2.9% PHB content and yield of 0.12 kg/kg-CP. PHB productivity was 0.80 ± 0.06 g/(L·h). Logistic and Luedeking-Piret models were used successfully to describe the profiles of bacterial growth and PHB production, respectively. Curve fitting using the Luedeking-Piret model revealed that PHB synthesis and PHB turnover occurred simultaneously during the process. Overall, the results demonstrated that cassava processing wastes are feasible feedstock for PHB production by Paracoccus sp. KKU01.