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Sucrose Crystallization Prevention in Whey Protein Isolate Films
K. L. DANGARAN and J.
M. Krochta
Department of Food
Science & Technology
University of
California, Davis, CA 95616
Whey protein isolate (WPI) films plasticized with sucrose are high in gloss and have excellent oxygen barrier properties. As coatings, whey protein/sucrose solutions may be used as a water-based replacement for alcohol-based shellac coatings. In prior studies it was determined that as sucrose content of WPI films and coatings was increased, the appearance, barrier and mechanical properties were improved. However, over time gloss of coatings faded and films became weak and brittle. This was attributed to amorphous sucrose in the films and coatings crystallizing.
The objective of this study was to determine the amorphous properties (i.e., glass transition temperature and time to crystallization) of sucrose in both native and denatured WPI film matrices at a number of relative humidities to assess how film composition and environmental conditions affect sucrose crystallization rate.
Films were made and stored at constant temperature in three different relative humidities (33%, 44% and 53%). The lag time until amorphous sucrose crystallizes in the films was measured by monitoring moisture uptake over time. Using differential scanning calorimetry (DSC), the glass transition temperature (Tg) of the films stored in the various environmental conditions was also determined. Using isothermal DSC, the sucrose crystallization rate constants were determined for comparison to lag time of sucrose crystallization in the films.
Studies monitoring moisture uptake have found the crystallization of amorphous sucrose in denatured WPI films is observable after 24 hours of storage at room temperature in 53% relative humidity (RH). Films stored in 44% RH have observable sucrose crystallization after a few weeks of storage. Films stored in 33% RH are stable after 2 months of storage with no observable crystallization.
Results from this study will used to develop high gloss, water-based WPI coatings that do not experience deleterious sucrose crystallization. This will prevent loss of gloss and durability of the coatings over time.
For more information on Dr. Krochta’s work and the Food Science and Technology Department at UC Davis, please visit Dr. Krochta's Web site - http://foodscience.ucdavis.edu/fst/faculty/KrochtaWeb/index.htm.