Solvent-free hot-pressed zein films: Synergistic plasticization with glycerol, decanoic acid, and potassium hydroxide

Zein, a hydrophobic amino acid-rich storage protein from maize endosperm, holds considerable promise for food-packaging applications. However, conventional zein films are predominantly fabricated by solvent-casting methods, which are less amenable to large-scale production. This research focused on evaluating how the integration of glycerol, decanoic acid, and potassium hydroxide influences the structural and physical features of zein films fabricated through thermal pressing. Thermal processing promoted the rearrangement of disulfide bonds and induced limited non-disulfide polymerization, accompanied by varying degrees of deamidation, without significant protein degradation. Potassium hydroxide promoted depolymerization and reduced porosity, whereas glycerol improved the dispersion of decanoic acid during melt processing. Potassium hydroxide, decanoic acid, and glycerol collectively enhanced the zein melt fluidity, thereby exerting a synergistic plasticizing effect that resulted in films with favorable extensibility. When the contents of glycerol, decanoic acid, and potassium hydroxide were 25%, 10%, and 4.5%, respectively, the hot-pressed film demonstrated well-balanced overall performance. This work provides both theoretical insight and practical evidence to support the solvent-free processing of thermoplastic zein-based films.