Effect of microwave-vacuum drying on some nutritional and quality characteristics of rosehips

Microwave-vacuum drying of rosehips (Rosa canina) was investigated and the effect of microwave power and vacuum level on some nutritional and quality characteristics was determined. Microwave-vacuum drying experiments were carried out at three microwave power levels (50, 100, and 150 W) and three pressure levels (4, 7.5, and 11 kPa (abs)). Rosehips were dried also by hot air (60 degrees C) and freeze-drying methods for comparison. Experiments were conducted until a moisture content of less than 10% by weight was achieved. Dried samples were subjected to some physical and chemical analyses. The final product obtained by microwave-vacuum drying was superior to the hot-air dried and comparable to the freeze-dried sample. Microwave-vacuum drying treatments were completed 75-195 min whereas 960 min was needed for hot air drying. It was shown that good quality dried rosehips with 75-90% of the initial vitamin C content can be manufactured by microwave-vacuum drying method.