Yoghurt powder (20 different sample) produced in a previous study [1] by the spray drying of fresh yoghurt at different feed, air inlet, and air outlet temperature combinations, following the scheme offered by the central composite rotatable design (CCRD), including 20 experiments, were used as the test material. White plain yoghurt (14.2% total solids and 1.5% fat) was purchased from a local dairy factory (Pinar Dairy Products Com., Izmir, Turkey). The materials were kept refrigerated until used and/or analyzed.