Comparison of Nutritional Characteristics of Fresh and Freeze-Dried Donkey Milk

This study was performed in order to compare the chemical and nutritional properties of raw donkey milk and reconstituted milk samples made from freeze-dried donkey milk powder. Fresh donkey milk samples were collected from 18 Ragusana breed pluriparous donkeys. The freeze-drying process was performed on fresh milk using a lyophilizer programmed to operate for 1 h initial freezing at - 45°C followed by primary drying at 30 °C at 0.10 mbar pressure for 48 h and secondary drying at 5°C for 3 h at the same pressure. Reconstituted milk (90%, wb) was prepared dissolving 0.9 g of freeze-dried donkey milk in 10 ml of distilled water. Nutritional properties of freeze-dried donkey milk remained basically unchanged compared with fresh milk, obtaining very similar values as regard chemical composition, fatty acid profile and minerals content in both kind of milks. The results of the present study confirmed that freeze-drying is a relatively sparing method for preservation of short-lived products due to the fact that the main quality parameters of fresh milk are not significantly affected by the treatment, while the transport and the storage costs of freeze-dried milk are greatly reduced.