Whey protein isolate coating on LDPE film as a novel oxygen barrier in the composite structure

To examine the feasibility of whey protein isolate (WPI) coating as an alternative oxygen barrier for food packaging, heat-denatured aqueous solutions of WPI with various levels of glycerol as a plasticizer were applied on corona-discharge-treated low-density polyethylene (LDPE) films. The resulting WPI-coated LDPE films showed good appearance, flexibility and adhesion between the coating and the base film, when an appropriate amount of plasticizer was added to the coating formulations. WPI-coated LDPE films showed significant decrease in oxygen permeability (OP) at low to intermediate relative humidity, with an Arrhenius behaviour and an activation energy of 50.26 kJ/mol. The OP of the coated films increased significantly with increasing relative humidity, showing an exponential function. Although the coated films showed a tendency to have less oxygen barrier and more glossy surfaces with increasing plasticizer content, differences in the OP and gloss values were not significant. Haze index and colour of the coated films were also little influenced by WPI coating and plasticizer content. The results suggest that whey protein isolate coating could work successfully as an oxygen barrier and have potential for replacing synthetic plastic oxygen-barrier layers in many laminated food packaging structures. Copyright (C) 2004 John Wiley Sons, Ltd.