Study on drying methods of Rhei Radix et Rhizoma / 中草药

ABSTRACT

Objective: To explore the suitable drying methods for Rhei Radix et Rhizoma (RRR) with color, drying time, drying rate, and content of active ingredients as indexes. Methods: Rheum palmatum was used in the test and the color of RRR was studied according to Chinese Pharmacopeia 2010. The extract was obtained by hot-dip method. The contents of anthraquinone, gallic acid, and catechin were determined using HPLC. Results: RRR treated with oven-drying, shade-drying, sun-drying, and fumigated with sulfur-drying below 65 °C showed good color and the cross-section was claybank. The cross-section of RRR treated with oven-drying over 65 °C showed dark brown. The highest contents of extract and anthraquinone in RRR treated by sun-drying were 34.32% and 1.90% and followed by those treated by oven-drying at 45 °C with 33.53% and 1.68%, respectively. High temperature caused the decrease of anthraquinone in RRR. The contents of gallic acid and catechin reduced with the increase of temperature under the constant temperature oven-drying process. Conclusion: The suitable drying method for RRR is oven-drying at constant 45 °C or sun-drying.