Effects of different drying methods on the chemical, nutritional and colour of yerba mate (Ilex paraguariensis) leaves

Abstract

This work investigates the effect of different drying processes on chemical, nutritional and leaves colour characteristics for Ilex paraguariensis leaves. These processes were composed of typical drying techniques (roasting + rotary dryer and roasting + conveyor dryer), and cutting-edge techniques (microwave oven [MW], freeze-drying (FD) and oven dryer [OD]). The MW can be an alternative technique, this is because the content of phenolic compounds (77 mg/g), antioxidant capacity (DPPH and ABTS) (∼370 and ∼1040 μM TE/g), methylxanthines and caffeoylquinic acids (2-4 mg/g) were similar, and sometimes higher, to the conventional drying processes. Leaves dried with MW also exhibited satisfactory nutritional analysis for protein (16.4%), dietary fibre (52.3%), ash (6.4%), lipid (6.1%) and moisture (5.7%), implying that yerba mate is a potential source of fibre and protein. Furthermore, the MW preserved leaves green colour (high and low scores of b∗ and a∗, respectively).