The effect of incorporating different ratios of both non-heated and heated (95 C) buttermilk (BM) to corn starch (CS) films was analysed in terms of its structural, mechanical, barrier, optical and bioactive properties. The properties of the film forming dispersions (particle size distribution, c-potential and rheological behaviour) were also analysed. As the BM increased in the blend, both the average particle size and the apparent viscosity of the film forming dispersions were reduced. The low,degree of compatibility between both materials resulted in heterogeneous structures, where an interpenetrated protein phase in the starch matrix was observed as a result of the protein gelation when BM was heated. This affected the mechanical and barrier properties giving rise to more resistant and extensible, and less permeable films than in non-heated BM. Only films formulated with heated BM exhibited antioxidant activity, probably due to the release of the antioxidant peptides during thermal treatment of proteins. BM did not have any effect on the growth of Listeria innocua. (C) 2014 Published by Elsevier Ltd.