An improved food package comprises a cook-in film encasing an in situ aqueous medium cooked meat product. The film has a polymeric olefin containing inner surface in adhering relation to the cooked meat product. The film inner surface is treated by a cold plasma in a confined region which has been evacuated to a pressure less than atmospheric pressure and to which a selected process gas other than air and containing less than 30% nitrogen has been added which results in a gas plasma that reacts with a film surface during cold plasma treatment to increase the surface energy of the film to more than 44 dynes/cm and provide a film that is both heat sealable to the package with an acceptable bond strength for sealing the package, and capable of adhering in a uniform and well controlled manner to the cooked meat product during cook-in without purge. The polymeric olefin containing inner surface can be formed of linear low density polyethylene, for example, to provide a relatively low cost food package from material whose meat adhering and heat sealing properties have an excellent shelf life. The plasma treating gas is preferably pure oxygen or a mixture of oxygen and nitrogen containing less than 30% nitrogen.