moisture sorption isotherms in st. john’s wort (hypericum perforatum l.) flowers

varieties of st. john’s wort (hypericum perforatum l.) native to iran possess the largest percentage of hypercin in their leaves and flowers. isotherm curves show the relationship between the relative humidity and moisture content of the plant at a constant temperature. it is essential to understand the isotherms curves for successful storage and drying of the plant. this study used adsorption and desorption to determine the moisture equilibrium of st. john’s wort flowers at 40°, 50°, 60° and 70°c. moisture content was determined to be 0.11-0.84 using the gravimetric static method. five mathematical models (modified henderson, modified oswin, modified halsey, modified chung-pfost and gab equations) were used to compare the experimental data. the modified halsey and chung-pfost models were found to be the best models for describing desorption and adsorption isotherms curves.