engleski

Freezing effects on the viscosity of dairy desserts

Freezing process, depending on the rate of freezing os well as on the storage temperatures, has a significant influence on the food quality. Mostly, the products structure could be disrupted due to the water crystallizhation and different 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. For the purpose to enable longer 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 C) and b) quickly by liguid nitrogen (-192 C). After freezig, they were stored at two temperatures: - 14 C and - 24 C. Before and after freezing, as well as 6o days of storage, the rheological properties (viscosity) of desserts at 4 and 20 C 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, first of all by the kind and amount of hydrocolloids and whey protein 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 stored at -24 C had greater viscosity than those stored at -14 C. Storage temperatures have greater effect on the viscosity of quickly frozen desserts, than on viscosity of the slowly frozen desserts. Therefore, dairy desserts must be frozen quickly and stored at, as soon as possible, lower temperatures.

Dairy desserts; rheological properties; hydrocolloids; freezing

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