NEW YORK (Reuters Health) - The best way to cook vegetables while preserving their antioxidant powers depends on the veggie, new research from Spain shows.

Microwaving and griddling were generally best, while boiling and pressure-cooking tended to be the worst, but there were exceptions to these rules, Dr. A. M. Jimenez-Monreal of the University of Murcia and colleagues found.

"The results of this study serve as a database providing information on the effects of different cooking methods on the antioxidant potential of vegetables, and might encourage the food industry to recommend particular cooking methods to help maintain the antioxidant properties of vegetables that we eat," the researchers suggest in the Journal of Food Science.

They looked at how the ability of 20 different vegetables to neutralize or "scavenge" three types of free radicals was affected by boiling, pressure-cooking, baking, microwaving, griddling, or frying.

Effects varied widely among the different foods, the researchers found. Only one vegetable - artichoke -- maintained all of its antioxidant punch no matter how it was cooked.

Some veggies actually had increased antioxidant capacity after being cooked in certain ways, for example asparagus after boiling and eggplant after frying.

Most cooking methods preserved the antioxidant capacity of green beans, beets and garlic. Every cooking method but boiling increased the antioxidant activity of celery.

In general, microwaving or griddling -- heating the vegetable on a heavy skillet without oil -- did the best job of preserving antioxidant activity, Jimenez-Monreal and colleagues found. Corn was the exception, losing roughly 35 percent of its free-radical scavenging capacity after microwaving.

Boiling and pressure cooking generally caused the greatest loss of antioxidant capacity, with frying being a little better than these methods and a little worse than microwaving or griddle-cooking. "In short, water is not the cook's best friend when it comes to preparing vegetables," the researchers say.

They conclude that more research is needed to see how different cooking methods influence a vegetable's antioxidant activity after consumption.

SOURCE: Journal of Food Science, April 2009.