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Het koken van aardappels en de hoeveelheid kalium*
Uit een studie blijkt dat de nog aanwezige hoeveelheid kalium in aardappels afhankelijk is van de manier van bereiding. Kalium is een mineraal dat belangrijk is voor de regeling van het hartritme, zenuwen en spieren. Aardappels zijn rijk aan kalium. Door aardappels voor het koken in stukken te snijden, wat vaak gebeurt om ze sneller gaar te laten worden, verdwijnt tijdens het koken ca. 50% van de kalium. Bij heel klein gesneden aardappels is het verlies zelfs 75%. Als de hele aardappel gekookt wordt treedt weinig verlies van kalium op. Mensen met een nierziekte die weinig kalium in hun voeding mogen hebben zijn vaak gewend aardappels eerst enige uren in water te laten staan alvorens ze te koken. Dit blijkt volgens deze studie weinig meer effect te geven dan klein gesneden aardappels meteen te koken.
Cooking method key to potatoes' potassium level
Cubing your potatoes before boiling them can cut down on cooking time, but it will also shortchange you on potassium, a new study demonstrates.
Potassium is an important mineral that helps regulate the heartbeat, conduct nerve impulses and contract muscles. Most adults need 4,000 to 4,700 milligrams (mg) of potassium per day -- with potatoes, tomatoes and bananas among the major sources.
In the new study, Drs. Paul Bethke and Shelley Jansky of the U.S. Department of Agriculture (USDA) found that cubing or shredding potatoes, then boiling them, drained the vegetable of much of its potassium.
This is important not only for the average consumer looking to get enough of the mineral, the researchers say, but also for people with kidney impairment, who generally have to limit their potassium intake.
The kidneys normally flush excess potassium from the blood so it cannot accumulate to toxic levels. People with kidney disease can risk serious side effects -- like weakness, numbness or even heart attack -- if they take in too much potassium.
Bethke and Jansky evaluated a few different potato preparations. In one test, they "leached" cubed potatoes by soaking them in water for hours; this tactic is often recommended to kidney patients as a way to drain potassium from potatoes before cooking them.
However, the researchers found that leaching did little to lower the tubers' potassium content, regardless of the potato variety they used.
In contrast, boiling alone reduced cubed potatoes' potassium levels by half, and lowered potassium in shredded potatoes by 75 percent.
The findings, according to Bethke and Jansky, suggest that simply boiling cubed or shredded potatoes is enough for kidney patients to reduce the potassium content.
"The data presented here show that it is not necessary to complicate the process by leaching tuber slices before boiling them," the researchers write.
On the other hand, healthy people would do well to opt for a different cooking method, Bethke and Jansky say. They note that boiling potatoes whole, rather than cut, reduces the potassium content by a much smaller percentage.
Similarly, baking, roasting and microwaving all seem to have minimal effects on potatoes' potassium content.
SOURCE: Journal of Food Science, (Augustus 2008)

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