The main actives, accounting for many of the biological properties of Mirtoselect^®, are anthocyanins (anthocyanosides).

The Vaccinium myrtillus L. (common name: bilberry or European blueberry) fruits are a well-known source of anthocyanins.
Prior et al.⁽¹⁾ reported that Vaccinium myrtillus berries contain the highest amounts of anthocyanins in comparison with other berries, including those of Vaccinium angustifolium. The amount of anthocyanins in the berries ranges from 300 to 698 mg/100 g⁽²⁾ and increases during the ripening process^(3-5). 

Different hundreds of anthocyanins, and more than 15 anthocyanidins, exist in the vegetal kingdom, although the greater part of them occurs rarely^(6-7). The term anthocyanin was initially coined to indicate the substance responsible for the color of cornflower: it derives from the Greek term anthos=flower, and kuanos=blue, and refers to a group of water-soluble pigments responsible for red, pink, mauve, purple, blue, or violet color of most flower and fruits. These compounds act as potent antioxidants and phosphodiesterase inhibitors, thus being particularly effective in the amelioration of capillary resistance and permeability.

Anthocyanidins present in low quantity in the Mirtoselect^® (<1%), are anthocyanins without the sugar moiety and should be considered anthocyanin degradation products occurring when there has been incorrect extract production and/or storage. Anthocyanidins are rare in nature and the metabolism of the anthocyanins produces only trace amounts of bioavailable anthocyanidins.