Abstract
Levulinic acid (LA) can be cost-effectively produced from a vast array of renewable carbohydrate-containing biomaterials. LA could facilitate the commercialization of the polymer poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) and PHBV-based products as carbon substrates. Therefore, this paper focused on the production of PHBV by Ralstonia eutropha with LA for hydroxyvalerate (HV) production, which plays an important role in enhancing the thermal properties of PHBV. Accordingly, the HV content of PHBV varied from 0–40.9% at different concentrations of LA. Stimulation of cell growth and PHBV accumulation were observed when 2–6 g L−1 LA was supplied to the culture. The optimal nitrogen sources were determined to be 0.5 g L−1 ammonium chloride and 2 g L−1 casein peptone. It was determined that the optimal pH for cell growth and PHBV accumulation was 7.0. When the cultivation was performed in large scale (2 L fermenter) with a low DO concentration of 30% and a pH of 7.0, a high maximum dry cell weight of 15.53 g L−1 with a PHBV concentration of 12.61 g L−1 (53.9% HV), up to 81.2% of the dry cell weight, was obtained. The melting point of PHBV found to be decreased as the fraction of HV present in the polymer increased, which resulted in an improvement in the ductility and flexibility of the polymer. The results of this study will improve the understanding of the PHBV accumulation and production by R. eutropha and will be valuable for the industrial production of biosynthesized polymers.
Highlights
Biosynthesized polyhydroxyalkanoate (PHA) polymers are currently attracting much interest from researchers because of their physical properties, which are similar to those of conventional thermoplastics, such as polyethylene (PE) and polypropylene (PP) [1,2,3]
R. eutropha could grow when Levulinic acid (LA) was used as the sole carbon source, the production of dry cell weight (DCW) and PHBV were lower (1.29 and 0.03 g L21, respectively) than that in the presence of additional carbon source (4.39 and 3.18 g L21, respectively) (Table 1)
50 mL of media was in 250 mL flask with 5% (v/v) inoculum under shaking conditions at 200 rpm for 72 h at 30uC. a5 g L21 LA was added as sole carbon source. b20 g L21 glucose was added as sole carbon source
Summary
Biosynthesized polyhydroxyalkanoate (PHA) polymers are currently attracting much interest from researchers because of their physical properties, which are similar to those of conventional thermoplastics, such as polyethylene (PE) and polypropylene (PP) [1,2,3]. The incorporation of other monomeric units into HB polymer chains can lead to copolymers with improved properties [13,14]. Work focused on improving the properties of PHB has led to the copolymer of HB and 3-hydroxyvalerate (HV), namely poly(3-hydroxybutyrate/3-hydroxyvalerate) (PHBV) [15]. When compared to PHB homopolymer, the PHBV copolymer has better physical properties such as impact resistance, toughness, flexibility and other properties involved in the manufacturing process. The performance of PHBV can vary greatly when this polymer contains different proportions of the HV monomer. Increasing the HV content in PHBV from 0 to 50% can significantly lower the melting point of the resulting polymer
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