Study on safe storage moisture content of Rhei Radix et Rhizoma using moisture absorbing math model / 中草药

ABSTRACT

Objective: The moisture absorption of Rhei Radix et Rhizoma (RRR) with different initial moisture content was studied under the conditions of relative humidity of 20%-85% and temperature of 5, 15, 25 and 35 ℃, respectively, so as to provide reference for the control of safe storage moisture and reasonable storage of RRR. Methods: RRR was stored at temperature of 5, 15, 25 and 35 ℃ and humidity of 45%, 60% and 75%, respectively. The samples were taken at different time points to determine its safe water activity with powder color and mildew as indicators. The isotherm adsorption data of RRR at 5, 15, 25 and 35 ℃ and water activity of 0.2-0.8 were obtained by static weighing method and six isotherm adsorption models, GAB, Oswin, Smith, Halsey, Henderso and Peleg, were used for fitting and evaluation. Results: The absolute safe water activity and relative safe water activity of RRR were 0.5 and 0.6, respectively. The adsorption isotherms of RRR at 5, 15, 25 and 35 ℃ were "S" type, which belonged to type II isotherm. Oswin model was the best fitting model and the model expression was Meq=A[Aw/(1-Aw)B. According to the model, the absolute safe water content of RRR with different initial moisture content at 5 ℃ was 9.00%, 9.59%, 8.00%, 6.71% and relative safe water content was 10.17%, 10.89%, 9.20% and 8.07%, respectively; The absolute safe water content of RRR with different initial moisture content at 15 ℃ was 8.24%, 8.83%, 7.24%, 5.86% and relative safe water content was 9.57%, 10.17%, 8.59% and 7.20%, respectively; The absolute safe water content of that at 25 ℃ was 7.17%, 7.75%, 5.73%, 4.70% and the relative safe water content was 8.72%, 9.26%, 7.26% and 6.25%, respectively; The absolute safe water content of that at 35 ℃ was 8.00%, 8.45%, 6.53%, 5.21% and the relative safe water content was 9.74%, 9.85%, 8.40%, 7.27%, respectively. Conclusion: Oswin model can be used to predict the equilibrium moisture content of RRR in storage, which can provide reference for the control of safe moisture and scientific maintenance of RRR.