Abstract

Vacuum microwave drying is one of the advanced drying techniques that has been widely studied and applied recently. In the vacuum microwave drying process, heat energy is supplied by electromagnetic energy to heat the material, under vacuum conditions. This paper presents the results of the study on the effects of vacuum microwave drying on drying time, total sugar content and protein content of purple sweet potatoes under different conditions of vacuum pressure (65, 75, 85 kPa) and microwave power (80, 240, 400 W); compared with the convection drying process using hot air when the product reaches the same humidity ≤ 5.0%. The results show that vacuum pressure and microwave power have an effect on the total sugar content and protein content of the sample after drying. The maximum total sugar and protein contents were 13.46 g /100 g of dry material and 3.27 g /100 g of dry material, respectively, under the conditions of 80 W microwave power, 85 kPa vacuum pressure and 20 min drying time. The total sugar and protein loss of the purple sweet potato sample dried by vacuum microwave was lower than that of the sample dried by forced convection with hot air with a significant difference (p ≤ 0.05).