Preparation of freeze-dried yoghurt as a space food

To develop a satisfying, calcium-rich food for consumption in space, white skim yoghurt, both plain and with added blueberries, was subjected to freeze-drying. Optimised freeze-drying parameters were extracted from the thermal analysis of the yoghurts, taking into account the role of the added ingredients. Rheological properties were not seriously affected by freezing, while the drying step resulted in an overall structural weakening of the reconstituted products, possibly as a consequence of the mechanical energy required for mixing with water. However, its viscoelastic properties were retained and the original strength could be recovered by modulating the amount of water. The freeze-drying process affected survival of the lactic acid bacteria, resulting in a 2–3 log population reduction. Mortality levels were reduced when sucrose and blueberries were added as ingredients.