Water Sorption Properties of Powdered Crude Drugs and Hydrophilic Function of Their Starches.

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Water sorption isotherms of powdered crude drugs and their starches were measured by a gravimetric method. The powder and the starch were prepared from the roots of Panax ginseng C.A. Meyer (PG) and Panax notoginseng (Burk.) F.H. Chen (PN), the rhizomes of Pinellia ternata (Thunb.) Breitenbach (PT) and Alisma orientale Juzepczuk (AU), and the seed of Coix lacrymajobi Linne var. ma-yuen Stapf (CL). The Guggenheim-Anderson-de Boer equation was well applicable to the water sorption isotherms. The optimum amount of water added to knead and to granulate the powders was approximately 25-28 (w/w)%. The water contents of granules or globules have to be determined on the basis of the isotherms at storage temperature and depend on the species of powders. The water sorption capacity of starch is high at water activity less than approximately 0.5 and it is higher at lower temperatures. The results of Gibbs free energy indicate the change in free energy of a water-starch solution formed by the water sorption was larger than that of the water-powder solution; that is, starch is more hydrophilic than powder. The enthalpy suggests water was sorbed endothermically on powders and exothermically on starches. The entropy suggests freedom of water was decreased in the solution and that those of powder and starch were reversed.
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