Microbial biopolymers and metabolites for potential applications in food packaging

The global transition toward sustainable materials has placed the packaging sector at the forefront of the circular bioeconomy challenge. In fact, conventional plastics, although effective, pose severe environmental concerns due to their persistence and dependence on fossil resources. In this context, the exploitation of microbial potential offers an innovative route for producing renewable polymers and metabolites that combine structural functionality with intrinsic bioactivity. This doctoral project investigated the production of microbial biopolymers and metabolites as building blocks for sustainable and functional food packaging, integrating safety assessment, microbial production, and waste valorisation. The work represents a first approach to connect biotechnology, materials science, and food preservation. A preliminary study, undertaken in collaboration with the European Food Safety Authority (EFSA) during a six-month Guest Scientist fellowship, proposed a safety-by-design framework for the evaluation of bio-based food contact materials originating from microbes or activated by microbial metabolites. In the project, the production of pullulan by Aureobasidium pullulans using agro-industrial by-products such as beet molasses and brewer’s spent yeast (BSY) was also taken into consideration, demonstrating the feasibility of circular carbon sources for microbial polymer synthesis. The subsequent valorisation of Saccharomyces cerevisiae biomass through high-pressure homogenisation, pulsed electric fields, and autolysis enabled the recovery of β-glucans, mannoproteins, and bioactive fractions with antioxidant and antimicrobial potential. These fractions were successfully incorporated into alginate-based edible films, PBS composites, and PLA/PET coatings, generating functional materials that preserved mechanical performance. When applied as edible coatings on cherry tomatoes, BSY-enriched formulations enhanced quality retention and shelf life. Overall, this thesis demonstrates how microbial biotechnology and agro-industrial by-product valorisation can converge to create safe, renewable, and functional materials for food packaging, advancing both scientific innovation and the goals of a circular and sustainable food system.