Cooking certain vegetables, either by griddling on a flat-metal surface without oil or microwaving, maintained the highest antioxidant level, according to a new study in the Journal of Food Science.

Researchers at the University of Murcia and the University of Complutense in Spain examined how various cooking methods affected antioxidant activity by analyzing six cooking methods with 20 vegetables.

The highest antioxidant loss was observed in cauliflower after boiling and microwaving, peas after boiling, and zucchini after boiling and frying. Green beans, beets and garlic kept their antioxidant levels after most cooking treatments. Vegetables that increased their antioxidant levels after all cooking methods were green beans (except green beans after boiling), celery and carrots. Artichoke was the only vegetable that kept its high antioxidant level during all the cooking methods.