Preparation of antioxidant konjac glucomannan-based films enriched with Ocimum gratissimum L. essential oil Pickering emulsion and its effect on walnuts preservation

The objective of this study was to prepare and characterize konjac glucomannan-based films (KZGO) enriched with Ocimum gratissimum L. essential oil (OGEO) Pickering emulsion stabilized by zein-gallic acid nanoparticles, and to evaluate its inhibitory effect on the oxidation of walnuts during storage. The formation, structure, interactions, thermal stability, mechanical properties, barrier properties and antioxidant activity of KZGO films were all investigated. KZGO film-forming emulsions were concentrated solution systems of entangled polymer dominated by konjac glucomannan linear molecules and exhibited shear thinning behavior. The OGEO droplets were homogeneously distributed in the continuous matrix of konjac glucomannan, increasing the roughness of KZGO films. The glass transition temperature, tensile strength and elongation at break, moisture resistance and UV shielding of KZGO films were improved due to hydrogen bonding interactions and good compatibility between components. The antioxidant activity of KZGO films was significantly enhanced, with the scavenging rate of DPPH radicals up to 91.87% and that of ABTS radicals up to 67.02%. Compared to polyethylene film packaging, walnuts preserved in KZGO-10 film packaging had lower peroxide value, thiobarbituric acid reactive substances and free fatty acids during 12 days of storage at 40 °C, indicating that KZGO-10 film packaging has better ability to inhibit lipid oxidation of walnuts. The results suggest that KZGO films have high potential for application in walnuts preservation.