Influence of drying method on steviol glycosides and antioxidants in Stevia rebaudiana leaves

The application of different drying conditions (hot air drying at 100 degrees C and 180 degrees C, freeze drying and shade drying) on steviol glycosides (stevioside, dulcoside A, rebaudioside A and rebaudioside C) and antioxidants in Stevia leaves was evaluated. Stevioside, the major glycoside found in fresh leaves (81.2 mg/g), suffered an important reduction in all cases, although shade drying was the least aggressive treatment. Considering the antioxidant parameters (total phenols, flavonoids and total antioxidants), the most suitable drying method was hot air at 180 degrees C, since it substantially increased all of them (76.8 mg gallic acid, 45.1 mg catechin and 126 mg Trolox, all equivalent/g Stevia, respectively), with respect to those present in fresh leaves (44.4, 2.5 and 52.9 mg equivalent/g). Therefore, the ideal method for drying Stevia leaves depends on their final use (sweetener or antioxidant), although, hot air at 180 degrees C is the most recommendable if only one treatment has to be chosen. (C) 2014 Elsevier Ltd. All rights reserved.