15C-23 |
Oxygen barrier properties of films made from CO2-precipitated casein |
P. M. TOMASULA, W. C. Yee, and N. Parris. USDA-ARS-Eastern Regional Research Center, 600 E. Mermaid Ln., Wyndmoor, PA 19038-8598 Films prepared from dairy proteins are hydrophilic in nature and their barrier properties deteriorate with increasing relative humidity (RH). Under conditions of low RH, however, theses films have been shown as effective barriers against water and oxygen. Unlike most protein films, films prepared from CO2 casein have been shown to have hydrophobic character; most likely due to the greater concentration of calcium (Ca) and phosphorus relative to that found in calcium caseinate. Our objective was to cast films using CO2 casein and compare their oxygen barrier properties to those of Ca caseinate and acylated casein films. Glycerol (GLY), with hydrophilic character, or a 3:1 ratio of GLY:poly(propylene glycol)(PPG), with PPG added to introduce hydrophobic character, were used as plasticizers. Oxygen transmission rates through the films were measured as a function of %RH in the range from 30% to 70% RH at 23C and in the temperature range from 10 to 40C at 40% RH, using an Ox-Tran 2/20 system. Films were double-sided masked with aluminum foil, placed in the test cell and exposed to oxygen. The GLY plasticized CO2 casein films were almost twice as permeable as the other films at the lowest RH studied and 23C and also at 40C and 40% RH. Their permeability approached that of the other films at 70% RH. The PPG plasticized CO2 casein films were as permeable as the other casein films over the entire range of RH. The slight structural dissimilarities in the films contribute to differences in their oxygen permeability only under conditions of low RH where the effects of water are not significant. The CO2 casein film, which does not dissolve readily under high moisture conditions, may potentially be used to coat dairy products to retard moisture loss.
Session 15C, Dairy Foods
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