Sucrose optimizes oxygen barrier property of whey-protein-coated films.

The oxidation of fats, oils and other food components produces off-flavors and off-colors, and causes a loss of nutrients. Protecting a product from oxygen is one of the most important requirements of a food packaging system. Whey proteins form transparent, flexible films when cast and dried from aqueous solution. These whey protein films have excellent oxygen-, aroma- and oil-barrier properties. Their properties may be better than those of protein or polysaccharide edible films and could be comparable to the best synthetic polymer films.

Common synthetic polyolefin films, such as polyethylene (PE) and polypropylene (PP), are excellent moisture barriers. But they must be coated or laminated with synthetic polymers, including ethylene vinyl alcohol (EVOH) copolymers and polyvinylidene chloride (PVDC), in order to create an oxygen barrier. The resulting structures are expensive and non-recyclable.

Replacing these synthetic oxygen-barrier layers with whey protein coatings could create a new use for whey proteins and perhaps improve the recyclability of the substrate film. Scientists examined the oxygen permeation properties of whey-protein-coated plastic films to compare their oxygen barrier performance as affected by temperature, relative humidity, substrate film and different proteins and plasticizers.

The researchers performed a corona discharge treatment on plastic--PE or PP--film surfaces using a laboratory corona treater. Whey protein isolate (WPI) or concentrate (WPC) coating solutions (10% w/w, db) were applied and spread evenly on the corona-discharge-treated substrate films. The investigators then dried the coatings at room temperature for 18 hours. Oxygen transmission rates were determined according to ASTM D3985 over a range of temperatures from 15 C to 40 C and relative humidities from 30% to 85%.

The researchers found that it was possible to form whey protein-based smooth and transparent oxygen-barrier coatings on PE and PP plastic films after the materials were treated with a corona discharge to modify their surfaces and improve their adhesion properties. Depending on the type of plasticizer, the resulting WPI- and WPC-coated films had excellent oxygen barrier properties at low to intermediate relative humidity levels. They were comparable to synthetic oxygen barriers. Among the plasticizers used, sucrose conferred the best oxygen barrier property to the whey-protein-coated films.

Further information. Seok-In Hong, Korea Food Research Institute, San 46-1, Baekhyun-dong, Bundang-gu, Seongnam-si, Kyonggi-do 463-746, South Korea; phone: [phone]; fax: [phone]; email: [e-mail].