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Rate of oil oxidation depends on oxygen barrier properties of edible films.

Recent research has the potential to enhance the utilization of fish skins, a valuable food processing byproduct. The research involves using both fish skins and edible films containing natural antioxidants that together can extend the shelf life of foods.

Scientists at the University of Idaho examined the film's physical properties and its oxygen and water barrier properties. First, they analyzed trout skin (Oncorhynchus mykiss) gelatin-based films containing the antioxidant epigallocatechin gallate (EGCG) and green tea powder. These materials were tested for their tensile strength, elastic modulus, elongation, and oxygen and water vapor transmission rates. In addition, the researchers determined the materials' in-vitro antioxidant activity using the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay. They also observed any effects the materials might have on cod liver oil held under mild thermal abuse conditions.

Cod liver oil overlaid with the gelatin-based films was stored at 40 C for 20 days. The samples were analyzed for their peroxide value and measured for thiobarbituric acid reactive substances (TBARS). Antioxidant activity remained in the films containing green tea powder, but declined in EGCG films after 20 days at 23 C. The water vapor transmission rate of the films that were incorporated with antioxidants did not change significantly. However, the oxygen transmission rate for films containing 50 ppm of EGCG and 20% green tea powder was high.

Other physical properties varied, depending on the amount of antioxidant that had been added by the investigators. The TBARS content and peroxide value of the control oil increased from approximately 0.05 to 4.71 per gram of organic compound malondialdehyde per kg of oil, and from about 3.6 to about 178.3 milliequivalents of peroxide per kg of oil, respectively, after 20 days.

For cod liver oil covered with the control or antioxidant-containing films, TBARS levels remained below 0.37 per gram of malondialdehyde per kg of oil. The peroxide value remained below 7 milliequivalents of peroxide per kg of oil.

Incorporating antioxidants into the films did not reduce oil oxidation at the levels tested. The rate of oil oxidation was more dependent upon the inherent oxygen barrier property of the films than the presence of antioxidants.

Further information. Caleb Nindo, School of Food Science, University of Idaho, Agricultural Science Building, Room 119, 606 Rayburn St., Moscow, ID 83844; phone: 208-885-9683; fax: 208-885-2567; email:
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Publication:Emerging Food R&D Report
Date:Sep 1, 2013
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