ANTIOXIDANT CAPACITY OF SELECTED LOCALLY AVAILABLE VEGETABLES

Introduction: Fairly large scale analyses have been done to evaluate the antioxidant capacity of vegetables and correlation between the various methods of analysis. However, very little has been done to relate the antioxidant capacities of these vegetables with their pH values. This study was carried out to determine the antioxidant capacity of selected widely consumed and locally available vegetables in Nigeria and relate the antioxidant capacity of these vegetables to their pHs. Methods: The vegetables were grouped into “green vegetables”-cucumber cabbage, lettuceand spring onions and “red vegetables”- tomato, scotchbonnet, cayenne pepper and carrot. The pH of these vegetables were determined. Two different methods-2,2-Diphenyl-1-picryhydrazyl (DPPH) assay and Ferric reducing antioxidant power (FRAP) assay were used to determine the antioxidant capacity. Results: Results of the pH measurements of “green vegetables” showed a range of 5.84-6.72 while the pH of “red vegetables” ranged from 4.87- 5.66.All vegetables used in this study had pH less than 7 with relatively high antioxidant capacity. Scotch bonnet had consistently high antioxidant activity regardless of the method employed. There was a significant negative relationship (P<0.05; r = -0.365) between the pH and DPPH radical scavenging activity and between the pH and total antioxidant capacity (P<0.05 r =-0.351). There was no significant correlation (P<0.05) between DPPH radical scavenging and total antioxidant capacity of all vegetables. Conclusion: The pHs of these vegetables were within the acidic range, and antioxidant potential of these vegetables increased with increasing acidity.