Dynamic analysis characterizes whey protein films.

The physical properties of a polymeric material strongly depend on its morphology and structure, as well as the relaxation processes it experiences from time to time. The process of dynamic mechanical analysis (DMA) is useful in determining the relationship between the structure, morphology and applicational properties of polymeric materials.

A plasticizer is an essential component in edible film formulation. However, its effect on the structure-property relationship of whey protein-based edible films is not well known. The main objective of work at the University of Vermont was to employ DMA to characterize whey protein-based edible films plasticized with glycerol.

Investigators wanted to gain a better understanding of the effect of plasticizer content on the structure-property relationship of whey protein-based edible films. Their effort provides a fundamental understanding of the structure-property relationship of edible films, which could help when designing and optimizing such films.

DMA measures the mechanical properties of materials when they respond to stress. DMA instrumentation is highly sensitive. These systems measure the stiffness and energy dissipation of viscoelastic materials as they are subjected to forces and resultant strains--displacements. The new instruments operate in precise temperature control from the cryogenic region to more than 600 C. They can evaluate materials ranging from rigid composites to weak gels. As such, the DMA process can accurately determine the glass transition temperature region and related factors.

Vermont scientists examined edible films based on whey protein isolate (WPI) and whey protein concentrate (WPC) which were plasticized with different amount of glycerol. The moisture content, water vapor permeability (WVP) and mechanical properties of the edible films were determined.

The moisture content, elongation and WVP of WPI and WPC films increased with the increase of glycerol content in the films. The addition of glycerol significantly impacted the films. DMA results revealed that whey protein films exhibited the behavior of a partially amorphous and semi-crystalline polymer system.

The researchers observed a higher compatibility in WPI films than in WPC films. The permeability, mechanical property and the glass transition of whey protein-based edible films were a function of glycerol content in the film system.

Further information. H. Chen, Northeast Dairy Foods Research Center, Department of Nutrition and Food Sciences, Terrill Hall, University of Vermont, Burlington, VT 05405; phone: [phone]; fax: [phone]; email: [e-mail].