Plant materials are the main source of natural antioxidants. Green tea, brassica vegetables, soy bean, garlic, onion and red grape are mentioned as the plants with the highest antioxidative potential. The total pool of antioxidants administrated with diet depends on two factors: the maintenance of antioxidants during processing and their bioavailability in human digestive tract. Particularly high losses of antioxidants causes prolonged cooking in large quantity of water. Significant losses are also occurred due to oxidation during drying and deep-frying processes. Microbiological treatment is generally recognized as less destructive.