The present work explores the antioxidant potential of Helichrysum stoechas (L.) Moench phenolic compounds for cosmetic applications involving the following steps: chemical characterization, microencapsulation and incorporation into a moisturizer.Eighteen different phenolic compounds were identified in flowering aerial parts (decoction and hydroalcoholic extract), being 3,5-O-dicaffeoylquinic acid and myricetin O-acetylhexoside the most abundant phenolic acid and flavonoid, respectively.Comparatively to the decoction form, the hydroalcoholic extract presented both higher antioxidant activity and higher phenolic content, being its lyophilized form chosen to

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 northeastern 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 EC 50 = 22.87 µg/mL and RP EC 50 = 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-Odicaffeoylquinic 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.

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A B S T R A C TThe 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 . 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.

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Salamanca, 2019 II III To my son…since 2001 making me stronger… IV V "Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fear less." Marie Curie VI VII DPTO QUIMICA ANALÍTICA, NUTRICIÓN

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