Polyhydroxyalkanoates (PHA) are biological polyesters produced naturally by numerous species of microorganisms, considered among the most promising alternatives to conventional plastics. These biopolymers offer mechanical properties comparable to those of materials such as polypropylene, polyethylene and polystyrene, but with a significantly lower environmental impact .

Thanks to their biocompatibility and versatility, PHAs find application in strategic sectors such as food packaging (responsible for a significant share of global plastic waste) and biomedical (sutures, valves, tissue engineering).

 

Despite their potential, their industrial production is still limited due to high costs (between 2 and 5 euros per kg), linked to the use of pure cultures, which require sterile conditions (and therefore expensive infrastructure and processes) and high-quality synthetic substrates, which represent up to 40% of the total process costs.

 

In the last decades, scientific literature has explored the possibility of producing PHAs using mixed microbial cultures (MMC) and organic waste substrates (e.g. agri-food waste, wastewater). This approach opens a new frontier that is cheaper and more sustainable, in line with the principles of the circular economy.

The process is based on a multistage configuration, which includes the fermentation of waste substrates for the production of volatile fatty acids (PHA precursors), the microbial selection to enrich the biomass in PHA-storing strains, and the accumulation phase, in which microorganisms, under nutritional stress conditions, synthesize and accumulate PHA inside the cell.

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The PHA represents an authentic bioplastic: it is produced by microorganisms, it is biodegradable in different environments and, moreover other than being potentially produced from organic waste. These characteristics differentiate it from other bioplastics on the market today, which although biodegradable, derive from food raw materials (such as corn or sugar cane), which entails high costs related to cultivation not to mention the impact on land use and the competition with the food production systems.