Antioxidant and Antimicrobial Properties of Selected Plant Leaves

Aims: To determine the antimicrobial and antioxidant potentials of some readily available plant leaves in order to source for alternate antioxidants and antibiotics.

Study Design: Randomized complete block design.

Place and Duration of Study: Department of Food Science and Technology, Federal University of Technology Akure Nigeria between Feb 2010 and Jan 2011.

Methodology: Ethanol, hexane and water extracts from leaves of Anacardium occidentale (cashew), Cocos nucifera (coconut), Citrus sinesis (sweet orange), Citrus limon (lemon) and Carica papaya (pawpaw) were prepared and screened for their antioxidant and antimicrobial properties. The total phenolic content (TPC) was determined by folin-Ciocalteu assay. Antioxidant property of the plant extracts were evaluated using inhibition of free radical 2, 2- diphenyl-2-picryl hydrazyl (DPPH). The antimicrobial activity of the extract against microorganisms (Acinetobacter spp., Bacillus cereus, Escherichia coli, Shigella dysenteriae, Staphylococcus aureus, Salmonella typhi, Aspergillus niger and Aspergillus flavus) was determined using modified agar-well diffusion method.

Results: Total phenol content (TPC) of leaf extracts based on tannic acid equivalent revealed that the TPC of cashew leaf ranged from 2.21 to 7.49 mg TAE/g, coconut leaf extract (0.59-2.22 mg TAE/g), lemon leaf extract (0.97-3.9 mg TAE/g), sweet orange (0.54-0.69 mg TAE/g) and pawpaw leaf extract (0.22- 0.36mgTAE/g). At 0.2mg/ml concentration, the highest antioxidant activity was observed from hexane extracts (45.03%-76.05%) followed by water extracts (45.82% -71.7%) and ethanol extracts (32.75%-56.79%). Ethanol extract (0.2mg/ml) from A. occidentale and C. papaya showed antimicrobial activity against all the eight microorganisms tested with inhibition zones ranging from 2-12 mm. The highest inhibition zone of 12mm was observed in A. occidentale leaf against Shigella dysenteriae while C. limon leaf had the lowest inhibition zone of 2 mm against B. cereus.

Conclusion: We may conclude that A. occidentale and C. papaya leaves demonstrated broad spectrum activities. The results provided evidence that the plant leaves investigated in this study might indeed be potential sources of natural antioxidant and antimicrobial agents if further investigated.