yoghurt powder production using a microwave–vacuum drier

dehydration, as one of the practical ways to increase the shelf-life and applicability of yoghurt in various foodstuffs, is normally done by freeze drier (fd) which is an expensive and time-consuming process. for these reasons, in the present study the capability of microwave–vacuum drier (mvd), as an alternative process, was investigated. for doing so, the fat free yoghurt samples of 2.2, 4.2 and 6.2 mm were dehydrated under various combination of absolute pressures (60, 200, 400, 600, and 800 mbar) and microwave powers (35,130, and 260 w) using a lab scale drier designed in our lab. based on our findings, the drying time of yoghurt in microwave–vacuum drier for thickness of 2.2 mm was considerably (80%) shorter than commercial freeze-drier. in addition, the dependency of the drying time to absolute pressure was much less than microwave power and yoghurt thickness. furthermore, except the color and bulk density, the rest of the qualitative parameters of yoghurt powders dehydrated by mvd and fd methods were almost similar. it should be noted that the highest resemblance in terms of quality and color indices between fd and mvd powders was seen at combination of low microwave power and low absolute pressure (35 w, 60 mbar). all in all, the findings of this study showed the capability of mvd for production of yoghurt and other food powders and this technique can be introduced as a potential alternative for fd.