Posted 12-4-01

Apple browning is a chemical or enzyme-based change that happens close to the fruit's surface.

When an apple is cut or bitten, for example, cells beneath the fruit's skin are damaged and exposed to oxygen. With help from an enzyme (polyphenoloxidase), the oxygen reacts with cellular substances called phenolic compounds. The result is polyphenol oxidase.

You probably recognize it as the brown, mushy part that quickly appears on areas of the apple's surface where you've bitten or cut it.

One way that chefs and cut-produce sellers delay browning is to treat sliced fruit with juice from lemons, grapefruit, limes, or other types of citrus. The reason is ascorbic acid (vitamin C) in the juice.

Use of this technique can delay browning for a few hours or even days. It does this by preventing oxygen from reacting with phenolic compounds that can lead to color changes and softening.

In Beltsville, Maryland, scientists with USDA's Agricultural Research Service are testing what may prove to be an even better way to delay browning in cut apples. Using a combination of natural products and low storage temperatures, they've figured out how to delay browning by several weeks rather than a few days.

It may even work for bananas, peaches, and other fruit. Eventually, with more testing, this could mean even more tasty and appealing cut-produce at the market.

Click here to read more about it in Agricultural Research magazine.

--Sci4Kids Staff using the following resources: American Chemical Society press release, "Apple Browning Significantly Delayed in USDA Tests"; Scientific American, "Ask the Experts," July 21, 1997; Nature Science Update, "Staying Delicious," by Sara Abdulla; Agricultural Research, "Keeping Freshness in Fresh-Cut Produce," by Doris Stanley, Feburary 1998.

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