Chemical composition and antioxidant capacity of stevia rebaudiana (VAR. MORITA II) leaves from Yucatan, Mexico

This study was carried out to evaluate the primary nutrients and dietetic fiber composition, as well as to determine the functional properties, of the Stevia rebaudiana (Bertoni) leaves when dried using one of two methods (convective drying and shade drying). Between the drying treatments, no differences were found for moisture content (7.5-7.7%), ash content (7.7-7.9%), crude fat (3.2-3.8%) or crude fiber (10.5-10.0%); however, crude protein (12.1-14.6%) and nitrogen-free extract (59.0-56.0%) showed significant differences. With regard to fiber fractions, these showed differences among neutral detergent fiber (17.8-16.2%), acid detergent fiber (13.7-12.3%) and cellulose (11.4-9.8%); on the other hand, acid detergent lignin (2.3-2.5%) and hemicellulose (4.1-3.9%) did not show differences. The results of total dietary fiber (38.2-32.8%) were equal for both drying treatments; however, there were differences in soluble dietary fiber (6.4-3.7%) and in insoluble dietary fiber (31.7-29.1%). Chlorophyll a and b contents showed significant differences between drying treatments, with values of 0.030-0.034% and 0.034-0.039% for chlorophyll a and b respectively. Carotenoid content did not show significant differences between drying treatments: 0.065% (convection dried) and 0.06% (shade dried). Both kinds of pigments are related to the antioxidant capacity of the extracts; in this sense, the Trolox equivalent antioxidant capacity values (417-423 mM/mg sample), ferric reducing power values (85-88%), copper chelating capacity (59-60%), and ferric chelating capacity (49-52%) did not show significant differences between drying treatments. The results indicate that stevia leaves dried using either method may be an ideal candidate for further research into their uses as a source of nutrients, fiber and antioxidant compounds.