Recent Trends in the Production and Recovery of Bioplastics Using Polyhydroxyalkanoates Copolymers

Polyhydroxyalkanoates (PHAs) are polyesters synthesized as a carbon and energy reserve material by a wide number of bacteria. These polymers are characterized by their thermoplastic properties similar to those of plastics derived from the petrochemical industry, such as polyethylene and polypropylene. PHAs are widely used in the medical field and have the potential to be used in other applications due to their biocompatibility and biodegradability. Among PHAs, P(3HB-co-3HV) copolymers are thermo-elastomeric polyesters that are typically soft and flexible with low to no crystallinity, which can expand the range of applications of these bioplastics. Several bacterial species, such as Cupriavidus necator, Azotobacter vinelandii, Halomonas sp. and Bacillus megaterium, have been successfully used for P(3HB-co-3HV) production, both in batch and fed-batch cultures using different low-cost substrates, such as vegetable and fruit waste. Nevertheless, in recent years, several fermentation strategies using other microbial models, such as methanotrophic bacterial strains as well as halophilic bacteria, have been developed in order to improve PHA production in cultivation conditions that are easily implemented on a large scale. This review aims to summarize the recent trends in the production and recovery of PHA copolymers by fermentation, including different cultivation modalities, low-cost raw materials, as well as downstream strategies that have recently been developed with the purpose of producing copolymers, such as P(3HB-co-3HV), with suitable mechanical properties for applications in the biomedical field.