The aqueous crude extract of purslane (Portulaca oleracea L.) was characterized for its antioxidant activity, total amounts of proteins, and phenol content. Furthermore, the kinetic parameters (Vmax and Km) of the enzyme polyphenol oxidase (PPO) in the crude extract of purslane were analyzed in the presence of the heavy metals (HM) Cu and Zn. Results indicated that the crude extract of purslane contains 0.847 mg/ml amount of proteins and 107.88 mg/ml amount of phenolic compounds. The extract’s ability to scavenge free radicals was demonstrated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) method,results, which showed 48.8% improvement over the control gallic acid. The optimal temperature for PPO activity was 40°C, and the optimal pH was 6.0. Moreover, results showed a high browning intensity after incubation for 100 minutes. Kinetic studies illustrated the marked effects of the HM Cu and Zn on the studied kinetic parameters of PPO by performing changes in the values of Vmax and Km. These HM can act as noncompetitive or uncompetitive inhibitors on enzyme kinetics. In conclusion, depending on the type and concentration of Cu and Zn, the presence of these HM reduces PPO action. Further investigation is needed to show the effects of other HM on PPO activity in purslane extracts.
Key words: Antioxidant activity, Browning intensity, Kinetic parameters, Phenol content, Protein content
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