Freezing effects on the viscosity of dairy desserts
1998
Hegedusic, V. | Herceg, Z. | Rimac, S. (Faculty of Food Technology and Biotechnology, Zagreb (Croatia)) | Skreblin, M.
The freezing process, depending on the rate of freezing as well as on the storage temperature, has a significant influence on the food quality. Predominantly, the product structure could be disrupted due to the water crystallization and differences in size of ice crystals. Therefore, it is important to know the intensity of these changes. Dairy desserts are of limited shelf life due to their composition and relatively high water content. In order to prolong the shelf life of these desserts, they could be preserved by freezing. This investigation was carried out with five dairy desserts prepared by mixing sugar, egg yolk, flour, whey and various hydrocolloids. Samples were frozen in two ways: (a) slowly, in a freezer (at -14 degrees Celsius), and (b) quickly, using liquid nitrogen (-196 degrees Celsius). After freezing, they were stored at two temperatures: -14 degrees Celsius and -24 degrees Celsius. Before and after freezing, as well as after 60 days of storage, the rheological properties (viscosity) of desserts at 4 degrees Celsius and 20 degrees Celsius were determined. All dairy desserts had a similar solid matter content, but their viscosity was quite different. It was influenced by chemical composition of solid matter, primarily by the kind and amount of hydrocolloids and whey proteins used. The results have shown that frozen dairy desserts had lower viscosity than before freezing. Smaller viscosity changes and greater viscosity were determined in quickly frozen desserts. Storage temperatures had a significant influence on the viscosity of dairy desserts. Quickly frozen desserts stored at -2.4 degrees Celsius had greater viscosity than those stored at -14 degrees Celsius. Storage temperature has a greater effect on the viscosity of quickly frozen desserts than on that of the slowly frozen desserts. Therefore, dairy desserts must be frozen quickly and stored as soon as possible at lower temperatures.
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