A diet rich in fruits and vegetables possess wide variety of antioxidant compounds that are very important for human health. The antioxidant capacity may be decreased or increased by thermal-processing. This study aimed to evaluate the antioxidant capacity by using DPPH method and by using different bacterial strains, S. aureus (Gram-positive bacteria) and E. coli (Gram-negative bacteria). Fresh vegetable and some fruit juices showed different values of scavenging activity. Pepper showed the highest scavenging activity. Under cooking conditions, 30 minutes of boiling, pomegranate, tomato, spinach and onion showed an increase in scavenging activity. Cooking in microwave for 15 minutes caused increase in scavenging activity for all fruits and vegetables except Pepper. Addition of vitamin C or fresh lemon juice to E. coli incubated with H2O2, protected the E. coli against the damaging effect of H2O2. In conclusion, processing of fruits and vegetables by boiling or by using microwave did not decrease antioxidant activity rather than, in some cases these cooking method increase the antioxidant activity.