Comparative study of color retention of dried stivia leaves (Stevia Rebaudiana Bertoni) by single-stage drying and multi-stage drying

Abstract

The color of dried stevia leaves is an important component quality and primary consideration of consumers when making purchasing decision. This study aimed to investigate an effect of single-stage drying temperature and multi-stage drying temperature on drying rate and color quality of dried stevia leaves. The drying conditions of single-stage drying temperature are at 50, 60, 70, 80 and 90^oC and multi-stage temperature for 80°C follows by 50°C and 90°C follows by 50°C. The drying rate of single-stage temperature required to reduce moisture content of stevia leaves from 5.23±0.41 to 0.075±0.003 g_water/g_{dry matter} was 0.0018-0.0179 g_water/g_{dry matter}*min. Where as the drying rate of multi-stage drying temperature was 0.0032 to 0.0076 g_water/g_{dry matter} *min. It was found that multi-stage drying temperature provided the higher drying rate and color retention than that of single-stage drying temperature. The results of these tests suggest that multi-stage drying temperature provided better color quality of dried stevia leaves in terms of color. It was found that the suitable conditions for multi-stage drying temperature were 80^oC for 30 min and 50^oC for 730 min. The color qualities of dried stevia leaves for multi-stage drying temperature in CIELAB system namely L*, a*, b* and TCD were 54.15±1.83, -10.41±1.99, 18.97±1.47 and 5.01±0.84, respectively. In addition, the Chroma values (C^*) and Hue angle (h^o) were 39.19±3.11 and 108.84±4.39.