Engineering Two Sustainable Packaging Platforms from Agricultural Waste: Microbial Melanin-Enhanced Single-Cell Protein and Bacterial Cellulose Films

This study proposes a sustainable biorefinery strategy to develop alternative packaging films by integrating three microbial-derived materials produced from agro-industrial residues. Cheese whey and citrus waste were used as renewable substrates for producing single-cell protein (SCP), bacterial cellulose (BC), and microbial melanin (MM). SCP consists of dried microbial biomass rich in protein, while BC is a renewable biopolymer with outstanding physicochemical properties. MM, a natural pigment produced by black yeasts, is a multifunctional biopolymer with considerable technological potential. In this work, SCP and BC were employed as two distinct film-forming matrices, whereas MM was incorporated into both types of films as a functional additive to enhance their performance. To the best of the authors’ knowledge, this is the first study reporting the incorporation of microbial melanin into both SCP- and BC-based films. SCP and BC were produced by Kluyveromyces marxianus EXF-5288 and Komagataeibacter rhaeticus UNIWA AAK2, respectively, while microbial melanin was produced by Exophiala phaeomuriformis EXF-6108 cultivated on citrus waste. Melanin incorporation enhanced UV-shielding performance in SCP-based films containing 20% melanin which exhibited markedly reduced UVC/UVB transmittance and increased opacity, while reducing water vapor permeability in all film formulations. Tensile strength of BC-based films produced from glucose and cheese whey was increased from 4.4 ± 0.9 to 6.0 ± 1.3 MPa and from 3.7 ± 1.7 to 8.5 ± 2.4 MPa, respectively, following melanin incorporation. Overall, the findings demonstrate that waste-derived microbial materials enable sustainable packaging and promote a circular bioeconomy.