Modeling of drying St. John's wort (Hypericum perforatum L.) leaves

Drying of agricultural crops after harvesting is an important operation that helps in preserving product quality and quantity, particularly for medicinal plants and herbs which undergo reduction of essential oils and changes of qualitative properties such as color, both of which influence the economical value of the product. Drying of medicinal plants is a delicate operation for removing product moisture, in order to reduce enzyme activity; thus containing growth of bacteria and pathogens, and preventing product deterioration. Drying process of St. John's wort (Hypericum perforatum L.) leaves was studied and modeled in this investigation. Independent variables included temperature at four levels (40, 50, 60 and 70 degrees C), air velocity at three levels (0.3, 0.7 and 1 m/s), and product depth at three levels (1, 2, and 3 cm). The experiments were performed as factorial with completely randomized design in three replications. Seven drying models, namely Yagcioglu, Page, modified Page, Henderson and Pabis, Lewis, two-term and Verma, were utilized to fit the data. The Page model was found as the best model having the highest R-2 and lowest chi(2), RMSE and P-values.