Bacterial spores have special significance in foods because they are much more resistant to physical and chemical antimicrobial treatment. Nowadays, there is interest in using natural products such as plant extract for food preservation. In this study, 26 of tropical medicinal plants and spices were screened for their sporicidal activity against the spores of Bacillus cereus. The spores of B. cereus was harvested after incubation at 30°C for 1 week and treated with various plant extracts using the method of Standard Operating Procedure for the AOAC (Association of Official Analytical Chemists) Sporicidal Activity. Glutaraldehyde was used as a positive control. Among them, Indonesian bay leaf (Eugenia polyantha Wight) inactivated more than 3 log of spores/ml of B. cereus (99.99%) at the concentration of 1% and completely killed B. cereus spores at concentration of 2.5%. These results suggest that Indonesian bay leaf extract has strong sporicidal activity against spores of B. cereus.
Edible medicinal plants are often used in the treatment of various ailments and spice in traditional food preparation. In this study, 45 of tropical edible medicinal plants extracts from Indonesia, Malaysia, and Thailand were screened for their antimicrobial activity against five standard microorganisms for food preservative namely Aspergillus niger, Candida albicans, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. The methanol extracts of Piper nigrum L. seed, Piper cubeba L. seed, and the root of Ligusticum acutilobum Siebold and Zucc. showed antimicrobial activity against five species of standard microorganisms. Among them, P. cubeba L. extract demonstrated the most susceptible against all tested microorganisms. Minimal inhibitory concentration (MIC) and minimal bactericidal or fungicidal concentration (MBC or MFC) were performed by the broth microdilution techniques as described by the Clinical and Laboratory Standard Institute. MIC values of P. cubeba L. extract to A. niger, C. albicans, E. coli, P. aeruginosa and S. aureus were 12.8, 1.6, 3.2, 6.4, and 1.6 mg/ml, respectively. P. cubeba extract killed A. niger, C. albicans, E. coli, P. aeruginosa and S. aureus with MBC values of 25.6, 3.2, 6.4, 12.8, and 3.2 mg/ml, respectively. The potent antimicrobial activity of P. cubeba L. extract may support its use for natural food preservative.