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.
