Investigate properties, permeability of whey-protein-coated paper.

Paper is the most widely used material for packaging foods and other products. It gives a product a good appearance, and prints and recycles easily. But since paper and paperboard have a porous cellulose structure, they don't function well as water-vapor, oil or oxygen barriers for packaged products. In addition, the hydrophilic nature of cellulose limits the water vapor-barrier properties of paper. Paper and paper board easily wet with liquid water and lose their physical and mechanical strengths.

Paper's surface is usually treated to improve its properties. Surface-sizing agents prevent excess water or ink penetration into the paper and improve its strength. Coating the paper improves its barrier to water vapor, oxygen and aromas. Packaging materials should have good water resistance to maintain their physical strength after their exposure to water.

Compared with some sizing agents and pigment adhesives, whey protein may offer some advantages in improving packaging material performance. Whey protein forms an intact water-insoluble film out of aqueous solution, due to the formation of intermolecular disulfide bonds after heat denaturation. Thus, such a whey protein film has a crosslinked structure.

Researchers at the University of Manitoba (Department of Food Science, Winnipeg, MB R3T 2N2, Canada) measured the wetting properties of whey-protein-coated paper, including water absorption rate and maximum water absorptiveness, with the goal of improving its performance as a surface sizing agent or pigment adhesive for food packaging material.

Investigators found that the whey protein isolate coating increased the surface energy of coated pulp paper, thus increasing water affinity. Increasing the hydrophilic property may be caused by filling the hydrophobic porous structure of the paper with whey protein coating. Whey protein coating also accelerated the water absorption rate and increased maximum water absorptiveness. Since the whey protein coating increased the hydrophilicity of the coated paper and smoothed the surface, the technique may increase printability of the coated paper when using water-based ink. The whey protein coating also increased the water vapor barrier property of pulp paper. The water vapor permeability decreased by 29.5%, compared to paper without the coating.

The results indicate that the printability of water-based ink on whey protein-coated paper would increase with faster and greater ink absorption. Although the coating accelerated water absorption, it also increased the water vapor barrier property.

Further information. Jung H. Han; phone: [phone]; fax: [phone]; email: [e-mail].