Effect of microwave-assisted drying methods on the physicochemical properties of beetroots

Abstract

In this study, fresh beetroots were dried by five different microwave-assisted drying methods, including high-power microwave drying followed by low-power microwave drying (HMD—LMD), high-power microwave drying followed by hot-air drying (HMD—HD), hot-air drying followed by low-power microwave drying (HD—LMD), high-power microwave drying followed by vacuum drying (HMD—VD), and vacuum drying followed by low-power microwave drying (VD—LMD). After drying, moisture content, color, and rehydration ratio as well as betalains and total phenolic contents of the dried beetroots were investigated. The drying time of each microwave-assisted drying method was also investigated. As for drying time, HMD—LMD lasted 46.0 min compared to VD—LMD which lasted 308.0 min. HD—LMD took 185.0 min less than HMD—HD (230.0 min) and HMD—VD (265.0 min). The beetroots obtained by VD—LMD showed the best color appearance, the highest betalain content and total phenolic content, but its drying time was the longest and rehydration ratio was the lowest. The beetroots obtained using HD—LMD showed the highest rehydration ratio. Considering physicochemical properties of dried beetroots and economics, HD—LMD is a recommended and suitable drying method.