Cinética de secagem e composição química do óleo essencial de folhas de Pereskia aculeata Miller

Abstract

Pereskia aculeata leaves are commonly used in the production of nutraceuticals and/or functional foods. Normally, the leaves of this species when harvested, present high moisture content, which is an undesirable factor and that can lead to degradation of the product. In this sense, aiming at the post-harvest quality, it is important that the moisture content is reduced shortly after the product is harvested, therefore, drying becomes indispensable. However, in this step care is imperative, since some of the chemical components present in the leaves, such as the essential oil, are thermosensitive. In addition to the care related to factors that may compromise the chemical composition, such as temperature and air velocity, it is necessary to verify the behavior of the product during this process. The objective of this work was to evaluate the drying kinetics of P. aculeata leaves and to adjust mathematical models to the experimental data, as well as to verify the effect of different drying conditions on leaf color and chemical composition of the essential oils. The leaves were dried at four temperatures, 40, 50, 60 and 70 ° C and two drying air speeds, 0.4 and 0.8 m s-1, in a completely randomized design with two repetitions. The experimental data on the drying of P. aculeata leaves were adjusted with different mathematical models traditionally used in scientific studies to describe drying kinetics. The rate of water reduction, the effective diffusion coefficient, the activation energy were also determined. After drying, the color of the leaves was evaluated by the direct reading of reflectance in coordinates of "L", "a" and "b". The extraction of the essential oils were also carried out by hydrodistillation, and afterwards, the identification and concentration of the substances present were made and the data were submitted to an principal component analysis. With the results, it was concluded that among the analyzed models, the Midilli was the only one that presents satisfactory adjustment in all the drying conditions; the water removal rate and the effective diffusion coefficient increase with increasing temperature and drying air velocity. With increasing temperature and drying air velocity, the values of the "L" coordinates decrease, indicating that there was a tendency to blacken the leaves, now for the "a" coordinate, their values increased, indicating that the leaves lost their characteristic color initial, and exhibit tendency to dark, and for the coordinate "b", the values decrease, signifying that the coloration of the leaves become darker. In addition, the increase in temperature of the drying air caused a greater effect under the color of the leaves, implying a greater color difference between the dry leaves and the leaves of the fresh plant. The drying process influenced the concentration of the substances present in the essential oil of P. aculeata. Drying at the 40 and 50 °C conditions at both drying air velocities provided the highest percentages of concentrations of the identified substances.