Assessment of the nitrogen fertilization effect on bioactive compounds of frozen fresh and dried samples of Stevia rebaudiana Bertoni
Marisa R.Barroso, Natália Martins, Lillian Barros, Amilcar L.Antonio, M. Ângelo Rodrigues, Maria João Sousa, Celestino Santos-Buelga, Isabel C.F.R.Ferreira
Centro de Investigação de Montanha (CIMO), Instituto Politécnico de Bragança, Campus de Santa Apolónia, 5300-253 Bragança, Portugal.
The present study aims to assess the effect of different nitrogen (N) rates on the chemical composition and antioxidant properties of stevia frozen fresh and dried leaves, and to define the best growing conditions to maximize the levels of bioactive compounds. In general, processing affects more significantly the tocopherol and sugar contents than N fertilization. The most abundant sugars were xylose, arabinose + fructose and sucrose, presenting dried samples with higher contents than frozen fresh ones, while the latter better retained tocopherols than dry samples. Regarding phenolic compounds, greater levels were found in dried samples and in those fertilized with 25 kg N ha-1. Leaves from plants fertilized with 25 and 50 kg N ha-1 also evidenced higher antioxidant activity, which seemed to be influenced by the phenolic composition. In general, N fertilization provides an improvement in the chemical composition and bioactive potential of stevia leaves.
Keywords: Stevia rebaudiana Bertoni, Chemical composition, Phenolic compounds, Nitrogen fertilization, Antioxidant activity.