Studies of antioxidants and antibacterial activity of oleoresins from selected spices

The antioxidant and antibacterial activity of oleoresins from fresh Citrus hystrix leaves and Alpinia galanga rhizomes were screened and determined. Petroleum ether was the solvent that used to extract the oleoresins from these plant samples. Antioxidants activity was initially screened by 2, 2-Diphenyl-1-picrylhydrazyl (DPPH) assay on Thin Layer Chromatography (TLC). There were four antioxidants compounds being from A. galanga rhizomes oleoresins while only three antioxidant compounds were separated from C. hystrix leaves oleoresins. The degree of antioxidant activity in A. galanga was also higher which indicated by the intensity of yellow colour spots on the TLC plate. DPPH free radical scavenging assay was the spectrometry method used to determine the antioxidant activity of the oleoresins. In this assay. A. galanga oleoresin also showed a higher percentage of scavenging compared to C. hystrix leaves oleoresin which ranged from 38.23% to 83.99 %. The 1050 for A. galanga oleoresin was also lower than C. hystrix leaves oleoresin. Antibacterial assay was screened by disc diffusion method. C. hystrix leaves showed inhibition against all three food-borne pathogens namely Staphylococcus aureus ATCC 25923, Escherichia coil ATCC 25922 and Salmonella spp. ATCC 14028 while A. galanga only inhibited Staphylococcus aureus. Hence, C. hystrix leaves and A. galanga rhizomes oleoresins have potential to develop into natural food preservatives where A. galanga rhizomes oleoresin can be a potent antioxidant while C. hystrix leaves oleoresin can be a potent antibacterial agent.