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K. L. DANGARAN and J. M. Krochta. Dept. of Food Science & Technology, Univ. of California, Davis, 1 Shields Ave., Cruess Hall, 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 water-based replacements 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 sucrose in the films and coatings changing from amorphous to crystalline state. In a past study, it was determined that cross-linked, denatured WPI films decreased the rate constant for sucrose crystallization significantly more than native films. The objective of this study was to determine the effect of crystallization inhibitors on sucrose crystallization rate constants in denatured WPI films. The four inhibitors studied were lactose, raffinose, modified starch and polyvinylpyrrolidone. A WPI/sucrose film without inhibitor was included as control. Films were made and then stored at constant temperature in four different relative humidities (23%, 33%, 44% and 53%). The weight of each film was measured periodically to monitor crystallization. When amorphous sucrose crystallizes, it loses water, and the weight of the film decreases. By modeling the data with the Avrami equation for crystallization kinetics, the rate order and rate constants for sucrose crystallization in WPI/sucrose films could be determined. Studies monitoring the WPI films at the four relative humidities showed that lactose, raffinose, and polyvinylpyrrolidone decreased the rate constant of sucrose crystallization compared to the control. The effect became more significant as the relative humidity increased. Results from this study will be 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.
Session 46, Dairy Foods: General
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