The effect of light irradiation on the antibacterial potentials of methanol root extracts of Zanthoxylum zanthoxyloides (Linn) was evaluated against some clinical isolates of gram-positive and gram-negative microorganisms using the agar diffusion method. The methanol extracts were exposed to three different sources of radiations: sunlight (28 days), tungsten lamp (72 h) and photoreactor (1 h, 365 nm) after which their antibacterial activity was determined. The colour of the extract monitored by colour visualization and TLC revealed significant colour changes for each treatment; yellow to very light yellow (sunlight and tungsten) while the photoreactor irradiated sample did not show appreciable colour change. The antibacterial activity of the extracts generally reduces significantly (p < 0.05) after exposure to the varied radiations. The results in this study indicate a possible compromise of the antimicrobial quality of herbal preparations containing Z. zanthoxyloides; this highlights the need for appropriate storage of such herbal products.
Key words: Zanthoxylum zanthoxyloides, radiation, antimicrobial activity, herbal products.
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