Effect of Seasonal Variation on the Secondary Metabolites and Antioxidant Activity of Callistemon citrinus (Curtis) Skeels (Myrtaceae) Grown in Eastern Cape of South Africa

Abstract

Callistemon citrinus belong to the kingdom plantae, family Myrtaceae and genus Callistemon. It grows in Australia but has been naturalized in South Africa. It is used as traditional herb to combat both gastro-intestinal and respiratory diseases, pain, diseases caused by bacteria and fungi infection. About 500 g of the air-dried leaves were pulverized each month and subjected to hydro-distillation using a modified Clevenger apparatus. Hydro-distillation of the fresh leaves of C. citrinus gave a pale yellow volatile oil with a strong scenty fragrance, about 97 components were identified in the 12 treatments analyzed each month. The key components were pinocarvone (1.25-6.17 %), pinocarveol (0.10-9.56 %), α-terpineol (5.24-9.94 %), α-pinene (7.45-22.75 %), limonene (24.08) and eucalyptol (14.69-72.35 %). The compositional profile of the leaves of C. citrinus varied between (January-December). Treatments under investigation revealed markedly qualitatively and quantitatively differences. Antioxidant capacity of the volatile oil of C. citrinus leaves evaluated also demonstrated significance influence of seasonal variation on its activity. The most exigent activity for DPPH free radical scavenging was recorded in the month of September (spring) with an IC50 of 0.50 ± 0.04 mg mL-1, while the most paramount activity for the ABTS assay was 0.94 ± 0.02 mg mL-1 in January (summer).The lowest activity were observed in the June (winter) collection with IC50 of 1.45 ± 0.00 mg mL-1 and 2.19 ± 0.05 mg mL-1 for DPPH and ABTS assays, respectively. Results show that seasonal variations affected the chemical compositions, oil yield as well as antioxidant activities of the volatile oil of the leaves of (C. citrinus); therefore, it is important to consider such effects for industrial and therapeutic purposes.