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Het stomen van groente lijkt veruit de beste methode van koken.

Door het koken in de magnetron van groente verwijnen bijna alle anti-oxidanten, door stomen bijna geen. In de magnetron verwijnen bijna alle anti-oxidanten waarschijnlijk door de enorme inwendige hitte die de magnetron opwekt. (zie schema) Door te blancheren voor het invriezen verdwijnen ook een derde van de goede nutriënten.

STEAMING is by far the best way to cook vegetables and microwaving them is the worst, according to a study that compared the nutrients left in broccoli cooked in different ways.

Cristina Garc'a-Viguera's team at CEBAS-CSIC, one of Spain's scientific research council centres, in Murcia, measured the levels of antioxidants such as flavonoids left in broccoli after steaming, pressure cooking, boiling or microwaving. Antioxidants protect our cells from damage by mopping up highly reactive chemicals called free radicals, reducing the risk of cancer and degenerative diseases. Steaming left antioxidants almost untouched, while microwaving virtually eliminated them, the team found (Journal of the Science of Food and Agriculture, vol83, p 1511).

Microwaves probably destroy more antioxidants because they generate higher temperatures, says Garc'a-Viguera. "Internal heating is much more damaging."

Pressure cooking and boiling have intermediate effects. Neither destroys as great a proportion of the antioxidants as microwaving. But many of the remaining antioxidants leach out into the water during cooking, leaving only 20 to 45 per cent of the levels found in raw broccoli (see Graph)

In a separate study in the same journal (p 1389), Riitta Puupponen-Pimiä at VTT Biotechnology in Espoo, Finland, found that blanching vegetables before freezing also decreases their nutrient content. It is standard practice for frozen food companies to blanch vegetables before freezing, to inactivate enzymes that would otherwise alter flavour. Her team looked at a range of compounds in over 20 vegetables. Blanching reduced antioxidant levels by up to a third, although the precise effect depended on the vegetable. Freezing also caused small losses. (april 2004)

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