When an apple is cut or bruised, it often turns brown. This discoloration, while visually unappealing, is a natural process. This article explores the reasons for apple browning and clarifies when a brown apple remains safe to consume.
The Science of Apple Browning
Apples turn brown due to enzymatic browning, a biochemical reaction. This process involves enzymes, specifically polyphenol oxidase (PPO), present within the apple’s cells. When apple tissue is damaged, such as by slicing or bruising, these enzymes contact oxygen from the air.
PPO then oxidizes compounds called polyphenols, found in the apple’s flesh. This oxidation converts colorless polyphenols into o-quinones, which react to produce brown pigments known as melanins. This reaction is similar to how human skin tans when exposed to sunlight.
Are Brown Apples Safe to Eat?
Apples browned solely due to enzymatic oxidation are generally safe to consume. This browning is a cosmetic change that does not indicate harmful bacteria or spoilage. While the appearance shifts, nutritional value largely remains intact, though some minor loss of vitamins, like Vitamin C, can occur.
The texture of a browned apple might become slightly softer, and its taste could be less crisp or tart than a freshly cut one. These chemical changes do not pose a health risk. If browning is the only change observed, the apple can still be enjoyed.
When Brown Means Bad
Not all brown apples are safe to eat, as browning can also signal spoilage. It is important to distinguish between harmless enzymatic browning and decay that could pose health risks. A spoiled apple will exhibit clear indicators beyond simple discoloration.
Signs for discarding an apple include visible mold, which can appear as fuzzy spots of green, white, or black. A distinctly mushy or slimy texture, beyond a slight softening, also indicates decay. An off-odor, such as a fermenting, sour, or vinegar-like smell, signals spoilage. If browning is widespread, very dark, and accompanied by any of these other signs, the apple is no longer suitable for consumption.
Preventing Apple Browning
Several methods can help prevent apples from browning after being cut. Applying acidic solutions is an effective strategy because acid lowers the pH and inhibits the activity of the PPO enzyme. Lemon juice, which contains citric and ascorbic acid (Vitamin C), is a common choice; a mixture of one tablespoon of lemon juice per cup of water can be used to soak apple slices for a few minutes. Salt water solutions (about half a teaspoon of salt per cup of water) can also prevent browning by limiting oxygen access and denaturing the enzyme.
Reducing oxygen exposure is another way to slow browning. This can be achieved by storing cut apples in an airtight container or tightly wrapping them in plastic wrap. Submerging apple slices in plain water for short periods can also create a barrier against oxygen. Storing apples in cold temperatures, such as in the refrigerator, slows down the enzymatic reactions responsible for browning, extending their fresh appearance for several days.