Abstract:
This research aims to study the antimicrobial activities of five selected plants, which were cinnamon bark, betel leaves, licorice, ginger, and galangal and select the most effective herbal extracts to be evaluated for their preservative efficacies in aqueous gel formulation. The sequential solvent extraction using hexane and 95% ethanol was used to extract bioactive constituents in the studied plants. After completely evaporated the solvents, the crude extracts were tested for the antimicrobial activities against S.aureus TISTR 1466 (ATCC 6538), P.aeruginosa TISTR 781 (ATCC 9027), E.coli ATCC 7839, C.albicans TISTR 5779 (ATCC 10201) and A.brasiliensis DMST 15538 (ATCC 16404) by agar well diffusion method. The result showed that the cinnamon bark extract macerated in hexane could inhibit the growth of all studied micro-organisms and was more effective than betel leaves, ginger, galangal and licorice extracts, while its 95% ethanolic extracts obviously showed lower antimicrobial activities. The MIC and MBC or MFC of cinnamon bark extract against the testing micro-organisms were in a range of 0.039-0.312 mg/mL and 0.156-1.250 mg/mL/0.078-0.625 mg/mL, respectively. The effective doses of hexane extract of cinnamon bark attempted to be tested as preservative in aqueous gel formulation were 0.3%, 1.25% and 2.5% by weight, which were equal to MIC, 4MIC and 8MIC, respectively. The challenge tests according to ISO 11930 were carried out to determine the preservative efficacy. The results revealed that 1.25% and 2.5% of cinnamon bark extract satisfied the criteria B for bacterial strains and the criteria A for yeast and mold. The LC-MS data confirmed that the two main constituents in hexane extract of cinnamon bark were coumarin and cinnamaldehyde that might play a role in antimicrobial activity.
