Evaluation of the drying process and toxic metal contents in yerba mate cultivated in southern Brazil

Abstract

The drying kinetics of yerba mate leaves from southern Brazil was investigated theoretically and experimentally in a drying oven at 70°C. The effect of drying conditions on the moisture ratio, drying rate, and effective diffusivity of yerba mate leaves was evaluated. Five drying models were fitted to experimental data. Additionally, the concentrations of As, Cd, Pb, Ni, Cr, and Hg in the yerba mate leaves were determined using inductively coupled plasma optic emission spectrometry (ICP-OES). The results revealed that all samples only showed a falling rate period without a constant rate of drying. The Midilli model showed the best fit of experimental data. All samples showed levels of Hg higher than those permitted by Brazilian legislation. Monitoring programs and other studies are required to prevent the intake of yerba mate products contaminated with toxic metals.