Mechanical and barrier properties of extruded film made from sodium and calcium caseinates

Abstract

Over the past few years, much interest has been placed into the investigation of increased barrier and mechanical properties of protein films via a multitude of approaches. Generally, these techniques involve modifications of interactions among protein molecules, such as ionic crosslinking using divalent ions. To evaluate the crosslinking effect of Ca2+ cations, films were made from calcium caseinate (CaCAS) and/or sodium caseinate (NaCAS). The production of caseinate thin films was carried out in two steps: first thermoplastic pellets were made using a co-rotating twin-screw extruder, then they were transformed into thin films (60 μm) using a classical film blowing machine. Tensile measurements were carried out at 60% relative humidity (RH) and 30 °C using a homemade testing machine which allows the change in environmental conditions during the test. The films mechanical resistance was found to be affected by the presence of Ca2+ ions; films made from CaCAS were rigid and less flexible than those based on NaCAS only. Water vapour permeability (WVP) and water diffusion were also measured. The reported data showed that films with only CaCAS or in mixture with NaCAS are less permeable to water vapour than those totally made from NaCAS. Likewise, the calcium ions were found to slow down the water diffusion. Films based on CaCAS only or in mixture with NaCAS appear to be more attractive for food packaging, and their applications could be extended to other packaging area.