Preparation and Characterization of Whey Protein Isolate-based Coating Solutions and Coated Papers with Different Plasticizers

Abstract

Whey protein isolates (WPIs) are a byproduct of cheese and milk processing. WPI-based films offer transparency and good gas barrier properties at a low relative humidity, along with numerous different functional groups. However, they are hydrophilic, which restricts their use, and feature poor mechanical properties like brittleness. In this study, we explored the properties of WPI based coating materials depending on the type and contents of plasticizers, to use as a barrier coating materials for paper. Coating materials of WPI/glycerol (GY) and WPI/sorbitol (SO) with different plasticizer contents were prepared by solution blending. These materials were then coated on the surface of paper. The morphological structure, burst strength, tensile index, elongation at break, air permeability, and surface properties of the WPI/GY and WPI/SO-coated papers were investigated and compared based on the type and content of plasticizer. Compared to the WPI/GY-coated papers, the cracking of coating layers on the WPI/SO-coated papers was mitigated with increasing SO content in the WPI matrix. The WPI/SO-coated papers exhibited a higher tensile index, elongation at break, and air barrier than the WPI/GO-coated papers. Surface property analysis revealed that the hydrophilicity of both coated papers increased with increasing plasticizer content. However, further research is needed to reduce the hydrophilicity in WPI-coated papers and improve the compatibility between WPI and the plasticizer to enable their application in packaging.