EFFECT OF DRYING METHODS ON CONTENT OF SOME NATURAL PIGMENTS IN URTICA DIOICA L. AND MELISSA OFFICINALIS L.

Abstract

Medicinal plants are usually marketed to the public in a dried form and in this form they can also be used for the needs of the pharmaceutical industry. Since the drying process can affect chemical changes in the plants several drying methods and conditions have been tested to preserve the quality and quantity of biologically active components. The objective of this study was to investigate the effect of convection oven drying at 25°C ± 1°C for 65 hours, microwave oven drying at 800 W for 45 seconds, and air drying with sun exposure at 25°C ± 1°C for 65 hours on the content of chlorophylls and carotenoids in leaves of two medicinal plants. The plants selected were stinging nettle (Urtica dioica L.) and lemon balm (Melissa officinalis L.). The content of the natural pigments was investigated in the prepared extracts by the UV-VIS spectrophotometric method. Results showed higher content of pigments in Melissa officinalis when microwave drying procedure was applied compared to the oven dried samples and the sun dried samples (air dried with sun exposure) but a significant difference was only observed in the content of chlorophyll b. In Urtica dioica the air drying technique with sun exposure can be considered to be a more suitable drying procedure which preserves a higher amount of all pigments. Sun dried Urtica dioica samples had significantly higher chlorophylls and carotenoids content compared to the oven dried and microwave dried samples. In general, air drying with sun exposure seems to be the most suitable drying method in terms of preservation of pigments under study. This technique represents the simplest and most energy efficient drying procedure.