PHA biosynthesis from palm oil and its by-products
Among the key features of tomorrow’s plastics are eco-friendly characteristics and sustainability. Microbial polyhydroxyalkanoates (PHAs) have attracted research and commercial interest because they can be used as biodegradable thermoplastics that can be produced from renewable resources. In addition, the biocompatibility of PHAs has also made it an important compound for a wide range of medical applications.
Oil palm currently accounts for more than a half of the total cultivated land in Malaysia, and its oil production is one of the highest among the producing countries. Palm oil products such as crude palm oil, crude palm kernel oil, palm olein and palm strearin, which are abundance throughout the country, are potential substrates for PHA synthesis. Besides that, by-products from the palm oil refinery processes, e. g. palm fatty acid distillate, palm acid oil and palm kernel acid oil, are also feasible carbon sources for bacterial growth and PHA production.
Recombinant Cupriavidus necator containing large amount
of P(3HB-co-3HHx) copolymer observed by TEM after negative staining.
Almost the entire cytoplasmic space is filled with PHA
Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] is currently the most promising bioplastic because of its properties that resemble polypropylene (PP) and low-density polyethylene (LDPE). The overall cost of P(3HB-co-3HHx) production was significantly reduced with the utilization of inexpensive and renewable resources from palm oil industry as the carbon feedstock. Results from shake flasks culture show that various palm oil products can be used to produce P(3HB-co-3HHx) at high yield and constant quality.
Poly(3-hydroxybutyrate-co-3-hydroxyvalerate [P(3HB-co-3HV)] is another interesting polymer due to its hardness and excellent processability. Currently, we are able to produce high amount of this copolymer (up to 90 wt% of dry cell weight) by using Cupriavidus necator H16 from a mixture of palm oil and suitable 3HV-generating carbon sources. P(3HB-co-3HV) with different 3HV fraction could be produced by manipulating critical cultural parameters. A high 3HV molar fraction significantly improves the impact strength, flexibility and processability of the synthesized copolymer.
In addition, P(3HB-co-4HB) is another commercially important copolymer possessing superior properties that are useful for applications in the medical and pharmaceutical fields as absorbable materials and as controlled drug delivery agents, respectively. Similarly, this copolymer could be produced from various palm oil products with the supplementation of precursors carbon sources that are structurally related to 4HB.
At the same time, glycerol and glycerol pitch are also feasible for the efficient synthesis of P(3HB) homopolymer by a locally isolated bacterium, which was identified as Burkholderia sp. Glycerol pitch is one of the wastes generated by the Malaysian oleochemicals industry whereas glycerol is the major by-product from the bioprocessing of biodiesel fuel. Efficient bioconversion of these surplus materials to P(3HB) would overcome waste management problems, and at the same time generate useful products such as bioplastics.
We are currently scaling up the production of commercially useful PHAs using 10-L and 100-L fermenters.