Enhanced oxygen barrier properties of sodium alginate coatings in humid environments: ionic crosslinking of sodium alginate by calcium ions released from calcium hydrogen phosphate and calcium carbonate

Sodium alginate (SA) was crosslinked by calcium hydrogen phosphate and calcium carbonate (CC), of which the rate was controlled by glucono-delta-lactone to decrease the pH and induce a slow release of Ca²⁺ ions. The crosslinked SA was coated on oriented polypropylene (OPP). The coated films exhibited a low oxygen transmission rate (OTR) under 0% relative humidity (RH). The SA coating crosslinked with CC 0.07 g/g SA exhibited a lower OTR under 50% RH than the OPP/pure SA film due to the dense matrix and the exposure of hydrophobic groups. The coated film was laminated with cast polypropylene, decreasing an OTR by 0.11 cm³/m²·day (0% RH). Additionally, the pouches using the resultant multilayer films exhibited stable oxygen barrier properties against the environment which weakly simulates a boiling process. Furthermore, the pouches efficiently delayed the oxidation of grapeseed oil. Overall, the developed coatings show potential as oxygen barrier layers in food packaging.