Preventing browning, then, becomes a question of how to put a stop to enzymatic browning. Most solutions involve blocking the oxygen in one way or another, reversing the oxidation reaction, changing the pH of the environment, or halting the reaction through exposure to either high or low temperatures. Often, on the industrial scale, these methods are used in concert to maximize their effect—say, by combining the powers of ascorbic and citric acids.
But that's not practical for the home cook who just wants to stave off browning for a short period. You know, so the apple slices don't turn the color of a muddy sponge while they sit on your cocktail party's cheese tray.
I've been playing with more practical methods to test out which one works best at home. In my tests, I used Red Delicious apples, which I selected for their tendency to brown relatively quickly. I repeated all my tests with Bartlett pears, which aren't pictured, since my results were the same as with the apples. Here's the short version: The best way to prevent browning is to soak the cut fruit in a saltwater solution half a teaspoon of kosher salt per cup of water for 10 minutes, then drain and store until ready to use.
The mild salt flavor can be rinsed off with tap water before serving. The best part is that even after rinsing, the browning is still just as effectively reduced. One of the easiest things you can do to prevent browning is to submerge the cut fruit in plain water, which reduces the amount of air, and therefore oxygen, that can get to it. Since a lot of fruits float, it helps to either lay a clean paper towel on top, which, once wet, will push them under, or to put them in zipper-lock bags with the air pressed out.
I did the latter, since it's easier to see the apple slices in the photos that way. A lot of people will tell you to squeeze some lemon juice into the water first, which acidulates it; lemon contains ascorbic acid, which not only lowers pH as does the citric acid also found in lemons but can also reverse the oxidation reaction through a process chemists call reduction.
In my tests, I used three tablespoons fresh lemon juice more or less equivalent to the juice of an average lemon per quart of water. Then, just for the heck of it, I also played around with citric acid in two different very strong solutions, sprinkling dry crystals of it directly onto the cut apple surfaces.
The concentrations of the acid in these samples were too strong for the apples to actually be edible, but it's interesting to see what higher levels of the acid can do. In this first photo, which I've defined as zero in the timescale though, technically, it took me a few minutes to bag it all up and arrange it on the table for the photograph to be taken , you can already see that the citric acid is keeping the cut surfaces ever so slightly whiter.
It's worth pointing out, though, that the light source in the photos was at right, illuminating the samples closer to it more than the ones on the left. To the naked eye under the room lights, I wasn't able to see the difference between the plain-water and lemon-water samples at all. For comparison's sake, note the white table surface underneath, which is a uniform shade of white, but in the photos appears darker at left as well.
Fifteen minutes later, and differences are already becoming more apparent—the light source at the right alone isn't responsible for the yellowing of the untreated apples on the top row at left. At 30 minutes, we have more significant browning of the plain apple slices. The plain-water sample in the bag at far left is maintaining its color better, but not as well as the citric acid samples in the two rightmost bags. 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!
Haha you basically did my science project for me! Thanks I wont plagiarizer only the important parts I will paraphrase! Thanks, pardon my spelling. Your email address will not be published. This site uses Akismet to reduce spam. Learn how your comment data is processed.
There are a number of ways to stop your apples from turning brown. Keep them covered in water — this stops the oxygen getting to the PPO enzyme inside. If they are going into a dish like a fruit salad, then you can dip apple pieces in lemon juice — there is citric acid in lemon juice that works as an anti-oxidant to stop the browning.
Pineapple and lime juice can be used in the same way. This works because there is a compound in honey that stops the enzyme responsible for oxidation. Additionally, this is one of the methods that will not unpleasantly alter the apple's taste. If you want to take the submersion method up a notch, you can add a little bit of citrus or pineapple juice to the water.
What do these juices have in common? They contain citric acid, which slows the chemical reaction and prevents browning. But there are actually a few ways to use juice in order prevent browning: 1 you can add two tablespoons of juice to water and submerge the apple slices, 2 you could submerge the apples into juice, or 3 you can simply squeeze lemon, lime, or orange directly onto the surface of the cut apple.
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.
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