Phase Separation in Gelatin/Zein Films: Structure–Property Correlation and Multi-Criteria Decision Making Evaluation for Food Packaging

Protein-based films are attractive candidates for biodegradable packaging, yet their performance is often compromised by phase separation when combining components with contrasting hydrophilicity. In this study, gelatin/zein films were used as a model system to elucidate how phase separation governs multifunctional properties. FTIR, XRD, TGA, and SEM analyses confirmed heterogeneous domains arising from immiscibility, which strongly influenced mechanical, heat-sealing, barrier, and optical behaviors. Zein incorporation improved tensile strength, water resistance, and UV-blocking capacity, while it simultaneously compromised heat-sealing strength, transparency, and gas barrier uniformity. To rationalize these trade-offs, a Multi-Criteria Decision-Making (MCDM) framework integrating the Analytic Hierarchy Process (AHP) and Technique for Order of Preference by Similarity to the Ideal Solution (TOPSIS) was applied, revealing that gelatin/zein blends performed worse overall than pure films. These findings demonstrate that phase separation can improve individual attributes without generating synergistic effects, emphasizing the importance of compatibility control and holistic evaluation in the rational design of biodegradable packaging materials.