Kinetics of drying in a Mentha crispa foam layer and adjustment of mathematical models

Mentha crispa is a plant commonly used in folk medicine to treat illnesses and has wide industrial application. Dehydration has been used for several types of plants in order to reduce the levels of water content and water activity, so that it would allow na adequate storage due to the conservation of the active principles. The objective of this work is to investigate the process of drying mint in a foam layer. The foam was physically characterized in terms of density, expansion percentage, air incorporation capacity and stability. Drying was carried out according to a factorial experimental design, in which the input variables were: temperature (50, 60 and 70 °C), concentration of foaming agent (3, 5 and 7 %) and stirring time (3, 5 and 7 min); and the output variables were: drying time and water content (Xbs) of the product. The physical properties of the foam depended only on the foaming concentration. The rise in the temperature significantly reduced the drying time and the water content of the foam. The Page, Henderson & Pabis, Newton and Modified Page mathematical models were adjusted to the experimental data and Page’s model was the one that showed to be the most adequate to represent the drying phenomenon.