In vitro antibacterial and antioxidant activities of Orthosiphon stamineus Benth. extracts against food-borne bacteria

Extracts of the Orthosiphon stamineus plant were tested for antimicrobial and antioxidant activities against selected food-borne bacteria in vitro. Whole O. stamineus plants (powdered) were extracted using various concentrations (0%, 25%, 50%, 75%, and 100%) of methanol. O. stamineus extracted with 50% methanol, 75% methanol and fraction 5 of a 50% methanolic extract demonstrated inhibitory activity against Vibrio parahaemolyticus. The inhibition observed with these O. stamineus extracts was comparable to the inhibition seen with the natural food preservative 5% lactic acid; this is likely due to the high concentration of rosmarinic acid found in the O. stamineus extracts. This study showed that the highest concentration of rosmarinic acid had the best antibacterial and free radical scavenging activities. This suggests that rosmarinic acid content is closely associated with antibacterial and free radical scavenging activities of O. stamineus extracts.