Supercritical carbon dioxide-based approach for the recovery and purification of polyhydroxyalkanoates from mixed microbial cultures: A green approach for bioplastics production

The widespread use of petroleum-based plastics has significant environmental consequences, including greenhouse gas emissions and long-term contamination of marine and terrestrial habitats. In contrast, bioplastics are a class of biopolymers, widely considered as the main alternative to conventional non-degradable plastics. Polyhydroxyalkanoates (PHAs) are a class of biodegradable polymers that have the potential to replace conventional polymers thanks to their similar properties. PHAs are currently produced using fermentation technologies, which require post-extraction purification procedures as well as the use of organic solvents for the removal of residual fermentation media to obtain high-quality products (e.g., medical devices). In the present study, supercritical CO2-extraction (scCO2) was employed as a green technology to selectively recover and purify PHAs from mixed microbial cultures using different multi-step protocols, including: the use of co-solvents (methanol, water and phosphate buffer solution) inside the scCO2 cell, pre- and post-treatment of the biomass (with enzymes and H2O2), employing different times (2 h to 4 h), temperatures (35 °C to 40 °C) and pressures (20 MPa to 35 MPa) for the scCO2-treatment. Among the tested protocols, the post-treatment of biomass with H2O2 and trypsin (scCO2-H2O2-trypsin) resulted in the highest PHA purity and recovery with 97.2 % and 97.3 %, respectively. The results demonstrate the importance of scCO2-based techniques as a valid alternative to conventional methods that use chlorinated organic solvents. This highlights the importance of green technologies as a turning point in the industrial production of biopolymers starting from a complex biomass feedstock.