Abstract
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=22.87μg/mL and RP EC50=28.79μg/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.
Highlights
The demand for natural sweeteners has been gaining more and more importance due to the great controversy associated with the use of some synthetic sweeteners as cyclamate, aspartame or acesulfame-K
Tocopherols and sugars composition The tocopherol contents determined in the oven-dried and frozen fresh samples of S. rebaudiana are given in Table 1, with the presence of three isoforms (α, γ- and δtocopherol), being α-tocopherol the majority compound in both samples
The highest value of total tocopherols was obtained in the frozen fresh samples, which is in concordance with Pinela et al (2011), who reported a decrease in tocopherols content in Cytisus and Genista plant species after shade drying
Summary
The demand for natural sweeteners has been gaining more and more importance due to the great controversy associated with the use of some synthetic sweeteners as cyclamate, aspartame or acesulfame-K. The steviol glycosides (E-960) are a group of natural sweeteners of generalized availability These compounds are obtained from Stevia rebaudiana Bertoni, a sweet plant native to South America (Carocho et al, 2015), belonging to the Compositae (Asteraceae) family. It is one of the 154 members of the Stevia genus and one of the only two species that produce sweet glycosides (Madan et al, 2010). The plants with commercial value are often stored for some time before use and an efficient conservation is very important to avoid the loose of bioactive molecules during this process. It should be highlighted that the studied samples were obtained in an experimental field with defined cultivation conditions in order to standardize S. rebaudiana production and, chemical composition
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