Grease and oxygen barrier properties of whey-protein-isolate coated paperboard.

Application: Heat-denatured whey-protein-isolate and native whey-protein isolate coating formulations showed similar excellent grease barrier properties compares with commercial polyvinyl alcohol and fluorocarbon coatings.

Environmental concerns over the use of certain synthetic packaging and coatings have prompted research in the area of alternative packaging. Considerable research has studied edible and biodegradable films and coatings from corn, wheat, soy, whey protein, and other materials. These natural polymers could potentially be moisture, grease, and oxygen barriers in many food packaging applications. Natural polymers can also serve as barrier coatings on paper and paperboard (PB). Such coatings might replace current synthetic PB coatings such as polyethylene, polyvinyl alcohol (PVOH), rubber latex, and fluorocarbon (FC) in toad packaging applications.

Whey protein films and coatings have excellent grease, barrier, and oxygen properties. Whey from cheese production is largely under-utilized because few opportunities exist for large volume, value-added use of whey components. Whey protein might replace commercial PB coatings such as PVOH and FC as a grease and oxygen barrier. This study determined the grease and oxygen permeabilities of whey-protein-isolate (WPI) coatings on PB.

Results and discussion

The wet film thickness for tests in this work achieved a final dried coating weight of 20-25 g/[m.sup.2] as Table I shows. Although the paper industry normally uses several coating applications to achieve the same coating weight, this study used one coating application for coating thickness and weight consistency.

For grease and permeability, no significant grease penetration occurred among heat-denatured WPI (DWPI), native WPI (NWPI), FC, or PVOH coatings. This indicated that both WPI coatings were comparable to commercial PVOH and FC coatings and highly impermeable to grease penetration after four hours. Area-stained (AS) values for uncoated (UN) PB were significantly higher than all the other treatments after four hours.

The grease test was extended to 16 hours to observe any differences in grease barrier performance among DWPI, NWPI, FC, and PVOH coatings. AS values for DWPI, FC, and PVOH did not increase significantly from four hours. AS did incrase for NWPI after 16 hours. The difference in performance between DWPI and NWPI was probably due to the difference in the physical structure between the two coatings. The denaturation of whey protein promotes intermolecular disulfide bond formation. This crosslinking of protein strands contributes to increased tensile properties of DWPI compared with NWPI. Visual observations of cracking in the NWPI coating at the end of the 16 hours of storage support this hypothesis. The increase in AS of the uncoated sample from four hours to 16 hours confirmed that extending the designated TAPPI test time to 16 hours induced further grease penetration.

Depending on the basis weight and type of pulp of the base sheet used, grease permeability measurements can vary. Grease does not diffuse through fiber walls like water but migrates through pores in the paper or PB by capillary forces.

Conclusions

DWPI and NWPI showed similar excellent grease barrier compared with commercial PVOH and FC after four hours. According to TAPPI testing, the four hour test time is sufficient to determine if a PB coating is adequate for many packaging applications requiring grease resistance. The extended 16-hour test time demonstrated that DWPI has potential for PB packaging applications that require a more resistant grease barrier. Research on the possibility of plasticizer migration phenomenon is necessary before commercial use. DWPI and NWPI coated on PB showed excellent oxygen barrier properties.

Coating         Coating                Coating
material   weight, g/[m.sup.2]   thickness, [micro]m

DWPI       24.5 [+ or -] 2.9      41.7 [+ or -] 7.4
NWPI       21.9 [+ or -] 3.9      10.2 [+ or -] 3.6
PVOH       19.2 [+ or -] 2.8      31.0 [+ or -] 16
FC                 NA                    NA

1. Mean ([+ or -] one standard deviation) coating weight and
coating thickness.

Chan is at the Department of Biological and Agricultural Engineering, University of California, Davis, CA 95616, USA. Krochta is at the Departments of Food Science and Technology and Biological end Agricultural Engineering at the same school. Address correspondence to Krochta at [e-mail].