Stability of the constituents of Calendula, milk-thistle and passionflower tinctures by LC-DAD and LC-MS

Abstract

As a part of our investigations on the stability of tinctures, we evaluated 40 and 60% v/v tinctures of Calendula flower, Milk-thistle fruit and Passionflower. These preparations are widely employed in phytotherapy, thus Calendula is used externally for anti-inflammatory properties, Milk-thistle and Passionflower are employed for hepatic injuries and in tenseness with difficulty in falling asleep, respectively. Aim of this work was to assess the chemical stability of their active or marker constituents from accelerated and long-term testing by using HPLC. For Calendula flower and Passionflower active constituents are not known, however, flavonoids seem to have a crucial importance for the activity, and thus are considered the markers of Calendula and of Passionflower. Active constituents of Milk-thistle are represented by silymarin that is a phytocomplex mainly constituted by three flavolignans: silybin, silychristin and silydianin. Our investigation showed a very low thermal stability of the constituents from accelerated and long-term testing and determined by HPLC-DAD and -MS analyses and was related both to the class of flavonoids and water content of the investigated tinctures. Thus, shelf-lives at 25 degrees C of the most stable tincture (Passionflower 60% v/v) was about 6 months and only about 3 months the stability of Milk-thistle tinctures.