Effect of glycerol and water activity on the processing and properties of egg white-based bioplastics

摘要

Protein-based bioplastics are a new generation of plastics and are suitable to be produced commercially on a large scale using the same manufacturing methods as petroleum-based plastics. However, proteins require thermoplasticization prior to undergoing these thermal processes. In a first study, the effects of plasticizer type (water and glycerol (GLY)) and amount (0.34, 0.48 and 0.64 Aw and 0, 35, 40 and 45% GLY) on the thermoplasticization of the egg white protein (EWP) were investigated using thermal studies, gravimetric analysis, and morphological studies. The results showed that the combination of 35% GLY content and 0.48 Aw yields an EWP network with a moisture content of about 12% and that this is sufficient to lower its second second-order transition temperature below 170°C, the temperature that marks the onset of thermal degradation of the EWP network. Under these conditions the EWP network can be thermoplasticized at 150°C with less than 15% degradation. The degradation can be reduced further by increasing the GLY content. In a second study, the EWP were compressed to develop egg white-based bioplastics and the effects of GLY (35, 40 and 45%) and Aw (0.34 and 0.48) on the physical, mechanical and morphological properties of compressed egg white-based bioplastics are investigated. Lighter, more reddish and less yellowish sheets with a decreased thickness and transition temperature, improved mechanical properties and constant moisture content can be obtained by increasing Aw. Increasing the GLY content results in the same type of changes but to a lesser extent and increased moisture content. Increasing both, water activity and GLY content, leads to a more pronounced effect in some of these properties.