Effect of cooking methods on antioxidant properties of vegetables

Fruits and vegetables are valued for not only the nutrients but also for the nutraceuticals like antioxidants in them. They are the most important dietary sources of nutraceuticals that are valued for preventing lifestyle diseases like cancer, diabetes and cardiovascular disease. Such foods should be cooked/processed in a way to retain the goodness of nutraceuticals. Retention of antioxidants during cooking such as boiling, pressure cooking, microwave cooking, stir-frying and frying of vegetables was investigated. Fresh and cooked vegetables were analysed for ascorbic acid content (AA), total polyphenols (TP), total flavonoids (TF), tannin and total antioxidant activity by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. Results showed that the AA, TP, TF, tannin and antioxidant activities were affected by cooking methods, the retention varying among individual compounds. Boiling, pressure cooking and microwave cooking brought about appreciable reduction in AA, TP, TF, tannin and antioxidant activity in vegetables, while frying and stir-frying showed less losses. The highest antioxidant retention was observed in frying followed by stir-frying, microwave cooking, pressure cooking and boiling. The study indicated that short time heat treatments such as frying and stir-frying help to retain the antioxidant properties of vegetables.