Effect of Zein Protein on Rheological and Hydrophobicity of Gellan Gum-based Food Packaging Film

Alternative food packaging materials derived from polysaccharides can potentially reduce the use of plastic material. Gellan gum (GG) is a polysaccharide with good film-forming properties (FFS) but is limited by its hydrophilic nature and poor barrier properties. Therefore, GG film was blended with hydrophobic zein protein to improve overall film hydrophobicity and barrier properties. This study aims to investigate the effect of incorporating hydrophobic zein protein on film hydrophobicity as well as film rheological, molecular and barrier properties. Zein/GG FFS exhibited shear thinning behaviour and increasing zein concentration increases viscosity. Zein/GG FFS also shows ‘true-gel’ behaviour, whereby Ǵ has a minimal dependency on angular frequency. Surface hydrophobicity is significantly (p<0.05) improved, as the water contact angle increased by 18.3° after zein addition. Moreover, the water vapour permeability reduced from 10.71 x 10^-4 gmmm^-2h^-1kPa^-1 to 7.96 X 10^-4 gmmm^-2h^-1kPa^-1 and oxygen permeability reduced from 30.89 mmolkg^-1 to 22.38 mmolkg^-1 following the addition of zein. These observations are likely due to the hydrophobic nature of zein, which repels water and favors the formation of intermolecular bonds (hydrogen bonds and electrostatic interactions). Overall, the incorporation of zein imparts favourable changes to film microstructure and this improves hydrophobicity and barrier properties of GG film.