What if apples never turned brown?

Cut an apple in half. The inside is white.

Wait a while. It turns brown! What if apples never turned brown?

Slice an apple for your lunch box and, by lunchtime, the pale slices may have turned a patchy brown. Bananas, pears and potatoes do the same thing once they're cut or bruised.

Brown apple slices are still fine to eat, but they don't look as tasty. So what if apples never turned brown? This lab is a thought experiment, and the clues lead to a hidden chemical reaction, a squeeze of lemon and some new kinds of apple.

Food scientists call the browning of cut apples enzymatic browning. The same reaction darkens cut pears, bananas and eggplants (University of Wisconsin–Madison Extension), and it gives raisins, prunes and apple cider their deep hues (UW–Madison).

This thought experiment asks what would change if apples never browned. It uses the question to explore the enzyme behind the reaction, why acids and cold slow it, and the genetically engineered apples designed to suppress it.

An apple is made of tiny boxes called cells. Cutting breaks the cells open.

The juices mix with air. That mixing turns the apple brown.

An apple is built from millions of tiny cells. Inside them are natural chemicals called polyphenols and a helper called an enzyme. Normally they're kept apart.

When a knife cuts through the cells, everything spills out and mixes, and oxygen from the air rushes in. The enzyme uses the oxygen to change the polyphenols into new chemicals, and those join up to make brown pigments. It all starts almost the moment you cut.

A knife spills the contents of apple cells across the cut surface. An enzyme, polyphenol oxidase (PPO), that had been held in check is released and, with oxygen, oxidizes polyphenols in the flesh.

The products, called quinones, react with other compounds to form brown pigments called melanins, the same family as some of the pigments in human skin. Apple varieties brown at different rates because their chemical contents vary (Science News Explores; University of Wisconsin–Madison).

Pretend apples never turn brown. Your apple slices stay white all day!

They might look yummier in your lunch box.

If apples never browned, sliced apples might stay pale and fresh-looking for hours. Lunch boxes, fruit salads and snack packs might all look more appealing.

But browning may also do a job for the plant. A food scientist at the University of Wisconsin–Madison says the reaction is believed to help protect the plant against pests and germs. So an apple that never browned might lose a little of that protection. These are ideas, worked out from what browning does today.

Removing browning would improve the appearance of cut fruit. But Rich Hartel of the University of Wisconsin–Madison notes that enzymatic browning is believed to be a plant defense, and some of its products have been shown to help ward off invading organisms.

A non-browning apple might therefore trade appearance for some loss of that defense; how much would matter is speculation. The same reaction also gives raisins, prunes and apple cider their deep hues, so a world without it would be different well beyond apples.

Lemon juice is sour. Sour juice slows the browning down.

The fridge slows it too. Cold makes the change go slower.

You can slow browning in a few ways. Enzymes are fussy: most can't work properly when it gets too cold, and they don't usually like acid. So slices kept in the fridge, or brushed with sour lemon juice, brown more slowly.

Lemon and pineapple juice have another trick. They contain vitamin C, also called ascorbic acid, and oxygen from the air reacts with it before it can reach the apple's enzyme. The reaction needs oxygen, so no oxygen means no browning.

Each remedy targets part of the reaction. Enzymes work only in certain conditions: most cannot function when too cold or too warm, and they do not usually like acidic conditions, so refrigeration and acidic juices slow PPO (Science News Explores). Lemon and pineapple juice also carry an antioxidant, ascorbic acid, which reacts with oxygen before the enzyme can (University of Wisconsin–Madison Extension).

Because the process needs the enzyme, its polyphenol substrates and oxygen together, removing any one of them, or slowing the enzyme, delays browning.

Scientists made new kinds of apple. They make less of the browning helper.

So their slices stay pale for longer.

Some scientists asked: what if the apple made less of the browning enzyme in the first place? In February 2015, the U.S. Department of Agriculture decided that two such apples no longer needed special rules, so they could be grown and sold. They were genetically engineered to make less of the enzyme, so they brown less when bitten, bruised or cut.

People have different views about genetically engineered foods. The apples took a few years to reach shops, and in 2025 a science magazine for young readers suggested looking for them in the supermarket. Ordinary apples brown at different speeds anyway, because what's inside them varies.

In February 2015 the USDA's Animal and Plant Health Inspection Service determined that two apples from Okanagan Specialty Fruits, genetically engineered to resist browning, were no longer regulated articles (Federal Register, effective 18 February 2015). Marketed as Arctic Granny and Arctic Golden, they suppress polyphenol oxidase, the enzyme involved in browning when fruit is bitten, bruised or cut (Growing Produce).

At the time, the trade press reported that the public had generally been hesitant to accept genetically modified produce, and the company expected the first small test-market quantities in late 2016. By 2025, Science News Explores was suggesting readers look for Arctic apples in the supermarket. Conventional varieties already brown at different rates because their chemical contents vary.