Secagem de folhas de erva-mate (Ilex paraguariensis) por micro-ondas: avaliação dos parâmetros de cor e perfil de fitoquímicos

Abstract

This study evaluated the drying of yerba mate (Ilex paraguariensis A.St.-Hil.) leaves by microwave-assisted heating, with the aim of assessing the feasibility of microwave drying for yerba mate leaves and investigating its impact on the physicochemical quality and bioactive compound profile of the final product. Initially, fresh leaves were characterized in terms of their morphological and physicochemical properties. Drying experiments were carried out in a domestic microwave oven, operating under different combinations of power and drying time. To evaluate the experimental conditions, a Central Composite Rotatable Design (CCRD) 2² was employed, including axial points and replicates at the center point. Color parameters were determined using the CIE Lab* colorimetric system, and hue, chroma, and total color difference (ΔE) were subsequently calculated. Bioactive compounds were extracted by an aqueous method and quantified for caffeine, theobromine, and chlorogenic acid content by high performance liquid chromatography. Total phenolic compounds and antioxidant activity were also determined using the DPPH method. Using regression coefficient analysis, the effects of microwave power and drying time were evaluated on the following responses: final moisture content, color parameters, bioactive compound profile, antioxidant activity, and effective energy consumption. It was observed that increasing the applied power resulted in a significant reduction in drying time and in the final moisture content of the leaves. Significant effects of power and drying time were observed on moisture content, total phenolic compounds, antioxidant activity, and energy consumption, whereas color parameters showed smaller variations under optimized conditions when compared to conventional industrial drying. Based on the response surfaces obtained, process optimization was performed using the desirability function, allowing the identification of operating conditions capable of maximizing the preservation of bioactive compounds and minimizing energy consumption. The optimal drying condition was determined at a microwave power of 850 W and a drying time of 285 s.