Optimization of polyhydroxybutyrate production by experimental design of combined ternary mixture (glucose, xylose and arabinose) and process variables (sugar concentration, molar C:N ratio).

Conversion of lignocellulosic feedstocks to polyhydroxybutyrate (PHB) could make lignocellulosic biorefineries more profitable and sustainable. Glucose, xylose and arabinose are the main sugars derived from pretreatment and hydrolysis of herbaceous feedstocks. Burkholderia sacchari DSM 17165 is a bacterium that can convert these sugars into PHB. However, the effects of sugar ratio, sugar concentration, and molar C:N ratio on PHB production have not been studied. In this study, a seven-run mixture design for sugar ratio combined with a 32 full factorial design for process variables was performed to optimize PHB production. A polynomial model was built based on experimental data, and optimum conditions for different sugar streams were derived and validated. The highest PHB production (3.81 g/L) was achieved with arabinose at a concentration of 25.54 g/L and molar C:N ratio of 74.35. Results provide references for manipulation of sugar mixture and process control to maximize PHB production.