Effects of oral dosage form and storage period on the antioxidant properties of four species used in traditional herbal medicine

Herbal infusions and decoctions in water are some of the most commonly consumed beverages in the world. Although water is not a good solvent for many of the active components in herbs, liquid preparations are rich in several bioactive compounds. Most of them have powerful antioxidant activity and have been related to medicinal herbs' properties. Herein, decoctions and infusions in water of lemon-verbena (Aloysia citrodora) aerial parts and leaves, fennel (Foeniculum vulgare), pennyroyal (Mentha pulegium) and spearmint (Mentha spicata) aerial parts with different periods of storage (0, 30, 60 and 120 days), were prepared. The effects of the method of preparation and storage period on their antioxidant properties were analysed. For all the analysed species, infusions gave better results than the corresponding decoctions. Spearmint infusions showed the highest antioxidant properties, at all the storage periods, probably due to the highest levels and synergy between phenolics, flavonoids and ascorbic acid found in this sample. Linear discriminant analysis confirmed that the length of storage period has a significant influence on the antioxidant activity and antioxidant content. Flavonoids and reducing sugars proved to be the parameters that most highly contributed to cluster individual groups according to different periods of storage.