Optimisation of Phenolic Content and Antibacterial Activity of Cosmos caudatus Kunth. Leaf Ethanol Extract Using different Drying Techniques

Cosmos caudatus Kunth. leaves contain alkaloids, flavonoids, tannins, saponins, and steroids that can act as antibacterials. Drying methods can affect the chemical content and antibacterial potential of plant leaves. This study aims to optimise the chemical content and the antibacterial activity of Cosmos caudatus leaves against Staphylococcus aureus and Escherichia coli using different drying techniques. The leaves were dried using four methods: direct sun, indirect sun (under shade), oven 40 ̊C, and air-dried. The extracts were then obtained by maceration using 70% ethanol. The phenolic contents were tested spectrophotometrically. The antibacterial activity was tested against two bacteria strains using the Kirby-Bauer test (disc paper) with different extract concentrations (5%, 10%, and 15%). The antibacterial activity was computed from the zones of inhibition. The study’s results showed the total phenolic content of C. caudatus Kunth. leaf extract by direct sunlight was 1.90 ± 0.06, indirect sunlight = 2.50 ± 0.02, air-dried = 2.51 ± 0.41, and oven (40°C) dried = 1.85 ± 1.01. Extracts from the different techniques produce different inhibitory zones against the bacteria strains. The direct sunlight-drying method has a greater inhibitory effect on S. aureus than E. coli, compared to indirect sun-drying, oven and air-drying techniques.  This suggests that different drying techniques influence the total phenolic content and antibacterial potential of ethanol leaf extracts of Cosmos caudatus.