Oxygen permeation properties of whey-protein-coated plastic films were examined to compare their oxygen-barrier performance as affected by temperature (15-40 degrees C), relative humidity (30-85% RH), base film (PE: polyethylene & PP: polypropylene), and protein type (WPI: whey protein isolate & WPC: whey protein concentrate). The resulting whey-protein-coated films showed increase in oxygen permeability (OP) as temperature increased, with an Arrhenius behavior, and activation energy of 10.9-12.1 kcal/mol, regardless of types of whey proteins and base films. Relative humidity had an exponential effect on OP of the coated films, with excellent oxygen-barrier properties at low to intermediate RH. Overall OP values of the whey-protein-coated PP were significantly lower than those of the coated PE, mainly due to the intrinsic permeation characteristics of the base films. No remarkable differences could be observed in the oxygen-barrier performance between WPI and WPC coatings. Results suggest that whey protein coatings could work successfully as an oxygen barrier under low moisture conditions and have potential as an alternative to existing expensive synthetic oxygen-barrier polymers in composite structures for food packaging applications. (c) 2005 Elsevier Ltd. All rights reserved.