Abstract: In this study, we compared the effect of three different drying methods: hot-air drying, intermittence microwave drying and vacuum freeze drying on the color and main bioactive components of Dendrobium officinale stems. The results showed that the best hot-air drying conditions were 90 ℃ and 4 h, the best microwave drying conditions were irradiation at 550 W for 48 min with 30 s intervals, and the best vacuum freeze drying duration was 11 h. The intermittence microwave dried sample had significantly higher contents of total polyphenols and polysaccharides than did the hot-air dried one, while no marked difference in total flavonoid content existed between them, suggesting that both classes of compounds could be preserved better during intermittence microwave drying. Vacuum freeze drying process was most effective in preserving the polysaccharides and color of Dendrobium officinale stems. Under the best drying condition, the maximum and average drying rate followed a decreasing order of intermittence microwave drying > hot-air drying > vacuum freeze drying. From the above results, we conclude that intermittence microwave drying has the greatest potential for application due to the advantages of fast drying rate and less destruction of bioactive phytochemicals.

Key words: Dendrobium officinale stems, hot-air drying, intermittence microwave drying, vacuum freeze drying