Total Phenolic Content and Antioxidant Activity of Standardized Extracts from Leaves and Cell Cultures of Three Callistemon Species

A comparative study was carried out with ethanolic (80%) extracts from leaves and cell cultures of three Callistemon species, namely C. lanceolatus (CL), C. viridiflorous (CV), and C. comboynensis (CC). Cell suspensions of the three species were grown in liquid Murashige and Skoog (MS) medium (100 ml) supplemented with 0.9 mg·g kinetin in combination with 1.1 mg·g NAA. The CL leaf extract was standardized to contain the highest amount of phenolics (104 ± 2.0 mg·g), followed by CC (95.8 ± 1.2 mg·g) and CV (79.8 ± 4.6 mg·g). On the other hand, cell cultures of CV contained more phenolics (14.9 ± 0.6 mg·g) than those of the other two species, CL and CC, which contained 12.2 ± 0.16 and 9.12 ± 0.16 mg·g, respectively. Nevertheless, CV leaf extract exhibited the highest antioxidant activity (91.4% ± 0.4%) at a concentration of 1000 μg·ml, comparable to 100 μg·ml gallic acid (90.8% ± 1.5%).