Chemical and Physical Speciications of Kot Namtao

Abstract

       Kot Namtao or Rhubarb is the dried rhizome and root of the genus Rheum comprising 3 species i.e. Rheum oicinal Baill., R.palmatum L. and R.tanguticum (Maxim. ex Regel) Maxim.ex Balf., family Polygonaceae. Kot Namtao have been used as laxative with astringent efect in Thai traditional medicine but standard speciication in Thai Herbal Pharmacopoeia is not yet designated. Thus, in 2013, the physico-chemical properties of 19 samples of Kot Namtao collected from China as well as herbal drug stores in Thailand, were vestigated. Results indicated that anthraquinones (contain at least 3 active substances: chrysophanol, emodin, rhein) and tannins were found in all samples. The physico-chemical properties in terms of contents of water-soluble extractives, ethanol-soluble extractives, moisture, total ash, acid-insoluble ash, and hydroxyanthracene derivatives as calculated in rhein, were 31.71 ± 4.06, 21.85 ± 7.50, 8.18 ± 1.13, 11.85 ± 4.35, 0.76 ± 0.38 and 1.66 ± 1.07% w/w, respectively. The expected values of water-soluble extractives, ethanol-soluble extractives and hydroxyanthracene derivatives calculated in rhein should not less than 27, 14 and 0.6% w/w, respectively, while the limits for moisture, total ash and acid-insoluble ash were should not be more than 10, 16 and 1% w/w, respectively. The results obtained from the studies will be the base-line information for the quality control of Kot Namtao which lead to further establishment of the standard speciications of Kot Namtao in Thai Herbal Pharmacopoeia.