Assessment of Phytochemical Contents and Total Antioxidant Capacity of Five Medicinal Plants with Cosmetic Potential under Three Different Drying Methods

Abstract

Drying allows the quick conservation of medicinal properties of herbal materials. However, the instability of bioactive compounds in medicinal plants which exhibit potent antioxidant activity and wide range of pharmacological properties may indicate a sensitivity to different drying treatments. Therefore, the objective of the present study was to determine the effect of shade drying, solar drying and oven drying on bioactive ingredients of five cosmetic potential plant leaves. Leaves of Centella asiatica (L.) Urb., Senna alata (L.) Roxb., Justicia adhatoda L., Ocimum tenuiflorum L., Hibiscus rosa-sinensis L. were dried to a constant weight using shade drier at 30-35 °C, solar drier at 30-40 °C and oven at 40 °C. Aluminum chloride colorimetric assay, Folin- Ciocalteau method, and Phosphomolybdate assay were employed to analyse the total flavonoid content (TFC), total phenolic content (TPC) and total antioxidant capacity (TAC) of ethanolic extracts of leaves respectively. All assays were performed in triplicate. Data was analyzed using one -way ANOVA and Tukey’s multiple comparison method. Results showed that significantly higher TFC, TPC and TAC of solar dried leaves of O. tenuiflorum (758.81±2.05 mg RE/100g DW, 3.54±0.71 mg GAE/100g DW and 22.56±0.38 mg AAE/100g DW respectively) and leaves of H. rosa-sinensis (89.72±1.38 mg RE/100g DW, 23.9±0.06 mg GAE/100g DW and 8.53±0.73 mg AAE/100g DW respectively). Solar dried C. asiatica and S. alata leaves showed high TFC and TAC while the TPC was high in oven dried leaves of C. asiatica and shade dried leaves of S. alata respectively. In contrast, J. adhatoda showed the maximum TFC in shade dried samples, the highest TPC in solar dried leaves and the maximum TAC in oven dried leaves. Moreover, there were no significant differences (p > 0.05) among drying methods in terms of antioxidant capacity and phenolic content of J. adhatoda. and antioxidant capacity of C. asiatica. Thus, it can be concluded that, solar drying of medicinal plant materials using solar drier would be an economical, efficient, and effective drying method for preserving bioactive compounds present in leaves of above-mentioned plants.