Characterisation of pigments and antioxidant properties of three medicinal plants dried under different drying conditions

In this study, the effect of drying procedure on the pigment levels of three traditionally used medicinal plants were determined and the contribution of the pigment compounds to the overall biological potential of these plant species was examined. The contents of total phenols, anthocyanins, carotenoids and chlorophylls a and b were determined spectrophotometrically, in fresh lemon balm (Melissa officinalis L.), marigold (Calendula officinalis L.) and borage (Borago officinalis), as well as in the same microwave dried herbs, freeze-dried herbs and herbs air-dried at room temperature. In order to evaluate the effect of drying conditions on the antioxidant properties of separate pigment extracts, the obtained extracts of carotenoids, chlorophylls, total phenols and anthocyanins were evaluated for their antioxidant capacity using the ABTS radical scavenging assay. According to the obtained results, different drying techniques affect different bioactive compounds. Fresh herbs were characterized with the highest contents of carotenoids and polyphenols, air-dried herbs exhibited the highest content of anthocyanins, while the highest content of chlorophylls was determined in freeze-dried herbs. Total phenol content of the analysed plants ranged from 10.75 mg GAE/g DM in microwave dried borage to 98.56 mg GAE/g DM in freeze dried lemon balm. The highest content of total carotenoids was determined in fresh marigold (1.41 mg/g DM), freeze dried borage contained the highest content of chlorophylls (7.67 mg/g DM), while air-dried borage contained the highest content of total anthocyanins (17.55 mg/g DM). The results of this study indicated that freeze-drying is the most efficient drying technique in terms of preserving the beneficial bioactive compounds, followed by air-drying at room temperature, which is usually applied in domestic preparation of natural herbal remedies.