What makes apples turn brown




















Mix in all the other ingredients apart from the butter. Melt the butter in the microwave. Your grown-up can cut the apples into 1cm thick slices while you are doing this.

Dip an apple slice into the melted butter, and shake off any drips. Put it into your powdery mix, and move it around until coated. Pop it on the wire rack. Continue to do this until all the mix or apples are used up.

Try dipping them in:. You also gave me information… for my science project! I will try to cook the recipes, but if some of the recipes have to have a oven, mom will be mad if I use the oven without permission!

I have a list of questions for you. Do you cook? What is your hobby? What is your favorite food? I love the food and you gave info aswell! My science fair is due a in a few months and its on oxidation on apples, I aboustly love how you included food, helpful info, and OMG, how to prevent it! In addition, both fruit juices are acidic and the lower pH that they bring about causes PPO to become less active. Heating can also be used to inactivate PPO enzymes; apples can be blanched in boiling water for four to five minutes to nearly eliminate PPO activity.

Be warned that cooking will affect the texture of the product. Enzymatic browning is not unique to apples. PPO—a mixture of monophenol oxidase and catechol oxidase enzymes—is present in nearly all plant tissues and can also be found in bacteria, animals and fungi.

In fact, browning by PPO is not always an undesirable reaction; the familiar brown color of tea, coffee and cocoa is developed by PPO enzymatic browning during product processing.

Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Take a look at the above photo. That's an image of the same samples after three hours and 15 minutes. At this point, the lemon-water sample second from left in the bottom row has browned more than the plain-water sample; this lines up with scientific studies I've read, which have reported increased browning when the apple is exposed to lower concentrations of ascorbic acid.

Meanwhile, the citric acid samples look practically bleached, while the skins have taken on a neon quality as even more pigments have been drawn out. At this point, all the samples were near inedible. The citric acid ones, of course, were inedible from the start unless you like the idea of Sour Patch Kid—style apple slices.

The plain- and lemon-water apples, meanwhile, had reached an undesirable level of browning, and both were waterlogged and unpleasant to eat. The lemon water also subtly altered the apple flavor with a distinct citrusy quality. I later did a series of tests with much lower concentrations of citric acid one teaspoon per quart of water , which I found more palatable, but they didn't work nearly as well at preventing browning. I wasn't able to find a concentration of citric acid that prevented browning well enough while also not tasting overly acidic.

I also did a test of simply rubbing a cut lemon all over the cut surface of an apple. You can see a photo of that below in the salt section, but I'll sum the results up now: Skip it, since it adds a heavy lemon flavor to the apple and only marginally reduces browning. My take on this: Soaking apples and pears is a method that works fine if you use plain water, but only for a very short time—I'd say less than 30 minutes, and ideally less than Any longer, and your fruit will brown while the texture suffers.

Lemon water, meanwhile, actually speeds up browning while changing the apple's flavor, so avoid it. Check out the time-lapse GIF below to see the apples brown over time like Gertrude's poem, it goes round as around as an apple Sodium chloride, or common table salt, is another chemical that can interfere with oxidation.

For my test, I soaked apple and pear slices for 10 minutes in a salt solution made from half a teaspoon of Diamond Crystal kosher salt dissolved in one cup of cold water.

I then drained them and let them stand for two hours alongside samples of untreated cut apple. In the photo above, the saltwater-soaked apple is on the bottom right, with two untreated apple samples to the left.

The top row contains my lemon-rubbed apple, at right, and its untreated control at left. As you can see, the saltwater apple resisted browning the best; even after two hours, when this photo was taken, it was still a respectable white color. The salt flavor is very mild on the surface of the apple—one taster didn't even notice it—but it's there.

The good news is that a quick rinse under cold running water completely washes away any traces of salt, leaving you with a fresh-tasting and -looking apple, well after it's originally cut. But here's even better news: Even after rinsing off the salt, the apple and pear slices continue to maintain their fresh white color. This means you can soak your fruit in the salt water for 10 minutes, then rinse it off, pat it dry, and put it out on a cheese platter for at least a couple hours without a major loss in quality.

Packing a lunch for your kids? They'll have fruit that looks freshly sliced for lunch, and they won't come home complaining that it tasted salty! Eventually, slowly, after several hours, the salted apple will start to brown. For most home cooks, that's not a big issue. Bottom line: Using salt is the most effective method I tested, with the least damage to the apple's texture and flavor. In case you're curious, extreme temperature can also be used to prevent browning, as you can see in the photo above.

The diced apple at right was blanched for two minutes in boiling water, then drained and shocked with cold water. High heat completely shuts down the browning reaction.



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