Large scale extraction of poly(3-hydroxybutyrate) from Ralstonia eutropha H16 using sodium hypochlorite

Abstract

Isolation of polyhydroxyalkanoates (PHAs) from bacterial cell matter is a critical step in order to achieve a profitable production of the polymer. Therefore, an extraction method must lead to a high recovery of a pure product at low costs. This study presents a simplified method for large scale poly(3-hydroxybutyrate), poly(3HB), extraction using sodium hypochlorite. Poly(3HB) was extracted from cells of Ralstonia eutropha H16 at almost 96% purity. At different extraction volumes, a maximum recovery rate of 91.32% was obtained. At the largest extraction volume of 50 L, poly(3HB) with an average purity of 93.32% ± 4.62% was extracted with a maximum recovery of 87.03% of the initial poly(3HB) content. This process is easy to handle and requires less efforts than previously described processes.

Figure 1

Fed-batch cultivation of R. eutropha H16 in a Biostat D-650 stirred tank reactor. The bioreactor contained 400 L of mineral salt medium with sodium gluconate as carbon source. A 20 L preculture was grown in the same medium. Cells were grown for 68 h at 30°C and harvested by continuous centrifugation. Due to technical problems, the concentration of carbon dioxide leaving the bioreactor could only be measured between the 40th and 58th hour.

Figure 2

Schematic diagram displaying the process for poly(3HB) production. (A) Cultivation of R. eutropha H16. (B) Separation of bacterial cells from the culture broth by continuous centrifugation. (C) Freeze drying. (D) Digestion of non-poly(3HB) cell matter by sodium hypochlorite with internal cooling and separation of the polymer through sedimentation. (E) Washing of the polymer with isopropanol with a small scale centrifuge. (F) Drying of the polymer through evaporation of isopropanol.