Posted 9-12-00

To get the answer, Sci4Kids checked with an expert, namely Dr. Kathleen Warner, a food scientist at the ARS' Food Quality and Safety Research Unit in Peoria, Illinois.

First off, the purplish color that results from salting the peas "doesn't cause harm," she says. So, you can scratch that off the worry list. Dr. Warner has a good idea why the peas change color when salted, though not why they turn purple versus some other color. "I can tell you that when you add acids or bases to food, it sometimes changes the pigment that's in there," she says. Pigments, by the way, are substances that give living things including plants and people their natural coloring.

Now, back to the peas... . "You can change the color of foods by adding chemicals, and salt is a chemical," says Dr. Warner. Can you guess what the formula for table salt is? Here's a clue: NaCl.

The color change that you noticed in peas didn't surprise Dr. Warner. "It's not super unusual," she says, especially if the peas were fresh and not canned. In fact, her lab sometimes shows kids how to do experiments to change the color of cabbage. They'll use lemon juice or baking soda. Baking soda changes a red cabbage's color to purple.

Cabbage and beets, for example, have a mixture of pigments, but not all of them are always seen by the naked eye, she says. So, you only see the dominant color. In peas, chlorophyll makes them appear green, and may dominate or "camouflage" other pigments, such as blues and reds. But then, someone like yourself comes along and sprinkles on some table salt and "presto"! The peas perform their magic trick.

-- Sci4Kids Staff, Kathleen Warner, food technologist/ research leader, USDA-ARS Food Quality and Safety Research Unit, Peoria, Illinois.

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