Preparation and characterization of homogeneous and enhanced casein protein-based composite films via incorporating cellulose microgel

Gelatin-coupled cellulose (GCC) microgel with whisker-like structure is prepared and used to incorporate into casein (CA) matrix to construct reinforced CA-based composite films by solution casting. The GCC microgel has excellent dispersibility and stability in water, which contributes to the hydrophobicity and significantly reduces the moisture absorption of the composite films, as well as a decrease in the water vapor permeability with an increase of GCC content at different relative humidity is also observed. Compared with pure casein material, the resultant CA-based composite films show more homogeneous and dense cross-sectional structure, and the cleavage temperature of the hydrogen bonds increases by 16 °C. In particular, their tensile strength and Young's modulus increase by 6 and 3.5 times, respectively. These indicators are superior to that of the nanoparticle enhanced CA-based composite film. Moreover, the light transmittance of the CA-based films at 550 nm is about 88% when GCC content is higher than 9%. The above results could be attributed to the strong hydrogen bonds formed between GCC components and CA matrix, as further confirmed by fourier transform infrared spectra and X-ray diffraction analysis.