Sustainable biopolymer films derived from banana peel waste: structure–property relationships and probiotic stability

The valorization of agro-industrial by-products as renewable polymer resources offers a sustainable approach for developing bio-based packaging materials. In this study, edible synbiotic films were produced from banana peel powder (BPP), and the effects of corn starch (S) and two probiotic strains, Lactiplantibacillus plantarum (Lp) and Bacillus coagulans (Bc), on film properties were comparatively investigated. FT-IR, XRD, AFM, and DSC analyses indicated that starch incorporation promoted a more organized polymer network through intermolecular interactions, resulting in modifications in surface morphology, wettability, and moisture-related properties. Although probiotic incorporation did not substantially alter the primary chemical structure of the films, it affected their functional characteristics in a strain-dependent manner. Antioxidant activity varied according to the probiotic strain, with DPPH radical scavenging activity reaching 80.59% in Lp-containing films compared with 63.26% in Bc-containing films. Antimicrobial activity was also microorganism-dependent, with the strongest inhibitory effect observed against Staphylococcus aureus. Both probiotic strains survived the film-forming process and remained viable throughout 35 days of storage. However, Bc exhibited greater stability, showing a viability loss of 1.3–1.4 log cfu/g compared with 2.0–2.3 log cfu/g for Lp. Despite these differences, all probiotic-containing films maintained viable populations of approximately 10⁷ cfu/g at the end of storage. Overall, the results demonstrate that formulation composition influences the structural organization and functional performance of banana peel-based edible films. The findings also highlight the potential of banana peel waste as a renewable resource for developing edible synbiotic packaging materials with tailored functional properties.