Production and characterization of sodium caseinate edible films made by blown-film extrusion

Abstract

Caseinates are considered as an interesting raw material for making biodegradable and water-soluble packaging. However, the development of plasticized caseinates, especially sodium caseinate, has mainly focused on the formation of films obtained by solution casting. This process, consisting in drying aqueous caseinate–plasticizer solutions spread on a hydrophobic plate, is not adapted to an industrial scale production. In the present study, a co-rotating twin-screw extruder was used to produce glycerol plasticized caseinate pellets. These transparent, homogenous, smooth pellets were transformed into thin films using a classical film blowing machine. Mechanical properties of the thermoplastic material have been measured as a function of glycerol content and environmental relative humidity and found to be greatly affected by glycerol and moisture levels. Water vapor permeability (WVP) of blown films was also investigated as a function of glycerol concentration, and it showed that the higher the glycerol content is, the lower the resistance to water transfer is. The obtained extruded sodium caseinate films are transparent, handleable and can even be edible. Several applications of these materials in food or non-food packaging could be developed.