Recovery and characterization of biodegradable poly(3-hydroxybutyrate)

Abstract

PHB recovery from Alcaligenes eutrophus and a recombinant Escherichia coli strain harboring the A. eutrophus PHA biosynthesis genes, characterization of cell powders containing PHB and recovered PHB, and a feasibility study for the commercial production of PHB were carried out. To take advantage of both differential digestion and solvent extraction, a new process for PHB recovery from A. eutrophus was developed using dispersions of sodium hypochlorite solution and chloroform. Using the dispersion, the molecular degradation of PHB by hypochlorite could be significantly reduced, minimizing the problems of conventional PHB extraction methods. Optimization of the dispersion treatment was conducted. The PHB recovery(%) from cell powder was maximized using a 30% hypochlorite concentration, a 90 minute treatment time, and a one to one (v/v) chloroform to aqueous phase ratio. Under this optimum condition, the recovery was approximately 91% and the purity of recovered PHB was greater than 98%. The number average molecular weight, $M_n$, of recovered PHB was about 300,000 and the weight average molecular weight, $M_w$, was about 1,020,000, in comparison to the original $M_n$ of 530,000 and $M_w$ of 1,272,000. The crystallinity of recovered PHB was in the range of 60~65%. As found in the subsequent studies, there existed an interesting relationship between the morphological state of PHB granules and the molecular degradation by hypochlorite during the recovery process. When PHB was recovered using a sodium hypochlorite solution, the amount of PHB degraded to a lower-molecular-weight compound was significant in the case of A. eutrophus, whereas the amount degraded in the recombinant E. coli strain was relatively negligible. On the contrary, there was no difference between the two microorganisms in the pattern of molecular weight change when PHB was recovered using the dispersions of sodium hypochlorite solution and chloroform. To understand these vindings, purified PHB an...