Fabrication and Characterization of Squid Protein–Whey Protein Concentrate Composite Films with Improved Stability

Protein-based films are promising biodegradable materials, but their performance is often limited by structural instability during storage. In this study, blend films were developed from myofibrillar proteins of giant squid (Dosidicus gigas) and whey protein concentrate (WPC) to improve functional properties and evaluate stability during three months of storage. The effects of plasticizer type (glycerol or sorbitol) and WPC concentration (5–15%) on film structure and performance were analyzed using Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetric Analysis (TGA), optical measurements, solubility, and water vapor transmission rate (WVTR). FT-IR revealed a transition from α-helix to β-sheet structures, indicating stronger protein–protein interactions, particularly in sorbitol-plasticized films. This structural organization improved barrier properties, reducing WVTR from 44.2 g·m−2·d−1 in squid protein films to 18.9 g·m−2·d−1 in films containing WPC. Light transmittance analysis showed that all films acted as effective UV barriers, with transmission starting near 350 nm. At this wavelength, transmittance ranged from 5–17% in sorbitol-plasticized films to 33–46% in glycerol-plasticized films. Increasing WPC concentration also reduced film solubility, indicating the formation of a more compact protein matrix. During three months of storage, FT-IR spectra revealed changes in the Amide A and Amide III bands associated with plasticizer migration and increased protein–protein interactions. Transparency increased during storage, indicating progressive structural reorganization, while the UV barrier properties remained stable. These results demonstrate that blending squid and whey proteins, particularly with sorbitol as plasticizer, produces biodegradable films with improved barrier properties and good structural stability during storage, highlighting their potential for sustainable food packaging applications.