Introduction
Many Australian native plants, including Syzygium spp., have been used as a traditional medicine by indigenous Australians; however, they have been underutilised in modern medicine due to the lack of scientific studies. The berries of Syzygium smithii, commonly known as lilly pilly, are considered to be a protective food and have not been investigated previously. This is a preliminary study of the antimicrobial and antioxidant properties of the berries and leaves of Syzygium smithii.
Method
Syzygium smithii berries and leaves were extracted using an in-house cold extraction method in ethanol and water. The antimicrobial properties were investigated using disc diffusion and minimum inhibitory concentration (MIC) assays against Gram-positive (Bacillus cereus, Enterococcus faecalis, Listeria monocytogenes, and Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Salmonella enterica). The antioxidant capacity was investigated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition, ferric reducing antioxidant power (FRAP), total phenolic content (TPC), and total flavonoid content (TFC) assays.
Results
During the disc diffusion assay, the berry and leaf ethanolic extracts showed inhibitory potential against all Gram-positive bacteria, except S. aureus for the berry extract. The MIC was found to be 25 mg/ml for the ethanolic leaf extract against all bacteria, excluding S. enterica, and between 12.5 and 25 mg/ml for the aqueous leaf extract against all bacteria, excluding K. pneumoniae and S. enterica. The TPC and TFC was found to be 663.44 µg gallic acid/mg and 489.80 µg quercetin/mg, respectively, with an antioxidant capacity with IC50 of 38.79 µg/ml against DPPH for the aqueous berry extract.
Conclusion
In conclusion, Syzygium smithii has the potential to be utilised by modern medicine as a potential antimicrobial and antioxidant agent. Further studies are needed to warrant these biological activities of Syzygium smithii.
