Studies with well-established cultivation conditions are of utmost importance in order to standardize the plants production and, therefore, its chemical composition. However, the conservation conditions may influence some of the bioactive compounds present in those plants. Stevia rebaudiana Bertoni samples cultivated in the north-eastern of Portugal, were exposed to different conservation conditions (oven-dried at 30 °C, for six days, or kept fresh by freezing (-20 °C) in the same period), and then studied for their antioxidant potential (including antioxidant compounds such as reducing sugars, tocopherols and phenolic compounds, free radical scavenging activity (DPPH) and reducing power (RP)). Oven-dried samples gave the highest antioxidant activity (DPPH EC50 = 22.87 µg/mL and RP EC50 = 28.79 µg/mL) and the highest total phenolic compounds concentration. The most abundant phenolic compounds in both samples were two caffeic acid derivatives, 5-O-caffeoylquinic acid (chlorogenic acid) and 3,5-O-dicaffeoylquinic acid. Otherwise, the highest values of total tocopherols and total sugars were registered in frozen fresh samples.
This study gives clues to choose the most appropriate methodology to preserve primary or secondary metabolites of S. rebaudiana, involved in its antioxidant activity.
The authors are grateful to the Foundation for Science and Technology (FCT, Portugal) and FEDER under Programe PT2020 for financial support to CIMO (UID/AGR/00690/2013), LSRE (Project UID/EQU/50020/2013) and L. Barros (SFRH/BPD/107855/2015) grant.
