You just cut an apple and, after a few minutes, it begins to blacken. It’s not bad, it’s not rotting, it’s just rusting. This oxidation is a natural and common process in the plant world. Luckily, humans have simple ‘tricks’ to avoid ending up snacking on a rusty apple.
Why do fruits and vegetables oxidize?
The answer to why apples rust shortly after cutting them is in the air. Literally. While the piece is whole, the skin protects the pulp or meat inside, full of water, a wide variety of vitamins, minerals and phytochemical compounds, such as phenols, among other compounds. When you peel it, that barrier disappears. The same thing happens when cutting it into pieces, since the internal tissues that contain those phenols that are potentially oxidizable in the presence of oxygen and by the action of the enzymes found in some fruits and vegetables, such as polyphenol oxidase, are broken.
Alfonso Rojas, director of the F&V Department at ALDI Spain, describes the oxidation process like this: “When coming into contact with oxygen in the air, oxidizable substances, such as phenolic compounds, are transformed into other substances that naturally acquire different shades. ranging from brown to reddish, or even black.”
Not all fruits oxidize the same way.
Rojas describes phenolic compounds as “a group of bioactive compounds with benefits for human health. «Plants develop them as a means of defense against free radicals, compounds present in the atmosphere that cause damage at the cellular level to both beings in the plant world, as well as animals and humans.»
The parade for Oxidation will depend on the amount of oxidizable compounds. that has its own fruit. There are species with a greater or lesser percentage of phenolic compounds, in the same way that within the same species, there are varieties with more or less compounds of this nature. Obviously, the longer we have the fruit or vegetable cut and exposed to the air, the greater the oxidation.
Effective methods to prevent oxidation
Oxidation can be prevented in two ways: by preventing the cut fruit from coming into contact with air and by slowing or preventing that chemical reaction. At home we can resort to various tricks to preserve cut fruit when we have to prepare it in advance. We can also apply these tricks if we have leftovers, since it is in good condition and throwing it away would be a waste of food.
The expert points out several tricks to prevent fruit (or vegetables) from oxidizing:
- The first and main It is cutting the fruit or vegetable just before consumption, or as close to consumption as possible.
- Apply a few drops of an acid suitable for food consumption.. This is the case of lemon, lime or vinegar. “Citrus juice has an acidic pH that will slow down this oxidation process,” says Rojas.
- Cover with plastic film.. In this way, we avoid contact with air.
- Put it in a zip bag. In this case, we have to try to extract as much air as possible from inside the bag before closing it. “Otherwise, it will slow down, but it will not be completely avoided because there will be oxygen left,” says Rojas. Another option is a vacuum sealer.
- Let it soak for a couple of minutes. Water creates a surface film that delays oxidation, however, this practice can reduce nutrient content if it is continued over time. It is important to keep in mind that if you take it out of the water, this trick will work temporarily, so it will have to be consumed immediately.
- Store it in the refrigerator in a tightly closed airtight container.. The closer it fits to the size of the piece, the less air there will be and therefore less oxidation.
- Freeze immediately. Keep in mind that when frozen, many will lose their crunchy texture. When defrosted, they will not be very good to eat raw, but they will be perfect for smoothies, purees, stews…
Is it safe to eat a rusty apple?
Oxidized fruit can take on an unappetizing appearance. However, the Oxidation is not a food safety problem.That is, you can eat a loquat, a banana or a rusty peach without risk to our healthand maintaining its nutritional value almost intact. Depending on the type of fruit, it can affect the content of some nutrients sensitive to light and oxygen, such as vitamin C and carotenes, in addition to the loss of phenolic compounds.
It is important to highlight that the effect of oxidation will be greater the greater the exposure of the fruit and vegetable surfaces to the air. That is, a peeled peach will have less surface area exposed to air than one that has been cut into 6-8 pieces.
Now, even if that piece with a darkened surface is safe, a rusty apple will be a visually less attractive snack in its appearance and color. It will also have a softer and less pleasant texture.
Keep peeled apples fresh: effective strategies
An apple cut up for school is an excellent lunch for recess at any age, even for the little ones. Or to drive to the park for a snack. The problem is that from the moment the parents prepare lunch in the kitchen until the little one goes to consume it, there are even hours in which browning due to oxidation will be inevitable. Something similar happens if we want to add some apple cubes to our salad.
“In these cases, the easiest thing is to lightly impregnate the inner surfaces of the apple with a few drops of lemon or lime juice. It is not necessary to also impregnate the skin, since it continues to perform its barrier function. Another alternative is to add some citrus fruit to the lunch box, such as some chopped orange or tangerine segments,” says the expert.
Stopping oxidation in salad is easier: just dress it with a splash of vinegar.
This prevents the cut avocado from oxidizing
Have you ever wondered why lemon or lime juice is added to guacamole? This citrus, in addition to providing an acidic touch, prevents oxidation. Avocado is sometimes large in size and is usually used in small quantities, so it is common to have a portion left over in some preparations. This is what happens if we want to add a few pieces to the salad or put some slices on breakfast toast.
If we have leftover avocado, the best tactic is to fill a container with water, add a few drops of lemon, submerge the avocado, taking care that the cut part is in the water, close and store in the refrigerator.
Goodbye to rusty artichokes
Artichokes are also very sensitive to oxidation. Rojas suggests “peel them and rub them with lemon. It is very effective, but it can be unpleasant if you don’t like that acidic lemon flavor. Another option, the preferred one, is to cook them immediately, so that the heat deactivates the enzymes that oxidize the phenolic compounds, that is, we peel them and boil them.»
The entry Rusty apple? Learn these tricks to avoid oxidation of fruits and vegetables was first published in Nutriiendo.
