Thin-layer chromatographic investigation of plant pigments in selected juices and infusions of cosmetological importance and their antioxidant potential

Fruit preparations (e.g., fruit juices and nectars) are rich in plant pigments and of great demand by the alimentary and pharmaceutical industry, basically not only due to their health-enhancing properties, but also due to their attractive colors and an overall high esthetic valor. Anthocyanins and anthocyanidins are an interesting group of plant pigments, and in this study, a thin-layer chromatographic detection was carried out of two anthocyanins (cyanin and keracyanin) and two anthocyanidins (pelargonidin and delphinidin) in a selection of the commercial and homemade fruit juices and the infusions prepared of dried plants. Moreover, the same preparations were evaluated for their antioxidant properties by means of two spectrophotometric methods (based on the 2,2′-azino-di-3-ethylbenzthiazoline sulfonate (ABTS) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) tests, respectively) and by the dot-blot test (based on DPPH). Finally, an effort was undertaken to correlate the chromatographically established occurrence of plant pigments in the investigated fruit preparations with their antioxidant properties. However, this correlation was not straightforward, and for at least two reasons. First, the four plant pigments considered are not the only secondary plant metabolites which exert an antioxidant activity. Second, different chemistries stand behind the two spectrophotometric antioxidant activity tests (ABTS vs. DPPH), and the different measuring techniques (spectrophotometry vs. dot blot) are assumed. Nevertheless, it was established that the juices and infusions with the highest detected numbers of plant pigments characterize with the high antioxidant activities also (with blueberries, chokeberries, and hibiscus flower on the top positions). In that way, confirmation of the antioxidant potential of the plant pigments was obtained. Moreover, the presence of certain plant pigments in fruit juices and plant infusions was reported for the first time.