The use of exoplysaccharide and dead bacterial cells in bioplastic production

The persistent nature of plastics in the environment causes serious global environmental problems, and especially single-use products pose a major threat to sustainability. Therefore, biodegradable bioplastics derived from renewable resources have emerged as strong alternatives to fossil-based plastics. In this context, the utilization of food industry wastes for bioplastic production contributes to waste management while enabling the development of value-added products. In this thesis, the production of both exopolysaccharides (EPS) and single-cell proteins (THP) was investigated using seven different lactic acid bacteria (LAB) strains (Enterococcus faecium, Lactobacillus sakei, Lactococcus garvieae, Lactococcus lactis subsp. cremoris, Lactococcus lactis, Weissella confusa, and Lactiplantibacillus plantarum) in a cheese whey (CW) medium for the purpose of bioplastic production. For EPS production, the parameters of nitrogen and carbon sources, pH, temperature, and incubation time were optimized in MRS medium. As a result, the L. cremoris strain achieved an EPS yield of 10.031 g/L. EPS was formulated with glycerol, gelatin, and citric acid, and bioplastic films were produced via the solution casting method; however, the resulting EPS films were found to be excessively ductile, sticky, and mechanically weak, indicating that EPS cannot be used as the main carrier in the bioplastic matrix. For THP production in CW medium, nitrogen and carbon sources, pH, temperature, and incubation time were optimized. Among the tested strains, L. garvieae provided the highest biomass yield, producing approximately 2.663 g/L THP. This biomass was formulated with glycerol, gelatin, and citric acid to develop bioplastic films using the solution casting method. Characterization studies showed that the films had a tensile strength of 7.139 MPa and an elongation at break of 18.56%. Thermogravimetric analysis (TGA) results indicated that the first major degradation occurred between 200–400 °C. In soil biodegradation tests, the bioplastics exhibited over 65% biodegradation after 60 days. In addition, Satureja hortensis essential oil (SH-EO) was incorporated into the films at concentrations of 1%, 2%, and 3% to impart antimicrobial properties. Disk diffusion analyses revealed inhibition zones of 13–19 mm against Staphylococcus aureus and 10–23 mm against Salmonella enterica serovar Typhimurium. The most pronounced effects were observed in bioplastics containing 3% essential oil, which exhibited inhibition zones of 15–16 mm against Escherichia coli—a response absent in the control group. The results demonstrated that although EPS exhibited limited performance in bioplastics, CW-based LAB-THP provided a strong and sustainable alternative for producing antimicrobial bioplastics via the solution casting method. This study contributes uniquely to the valorization of dairy industry wastes into value-added biomaterials and to the development of environmentally friendly and food-safe packaging solutions. Overall, this work represents an original approach by establishing a scientific foundation for the sustainable and antimicrobial bioplastic production from LAB-derived THP synthesized using low-cost waste such as CW.