July 18, 2024

It’s the subject of countless memes and a lot of frustration: avocados seem to turn brown almost instantly after you’ve sliced them.

Browning is a process that gradually changes the color of fruits and vegetables over time, affecting their overall quality (1).

It may happen for several reasons. A reaction involving the polyphenol oxidase (PPO) enzyme present in the pulp determines the rate of browning (1, 2).

Enzymatic reactions may occur during harvesting, transportation, storage, and processing. Mechanical and physical changes involving peeling, cutting, slicing, and dicing that lead to tissue damage are the most common causes of avocado browning (1, 2).

While avocado browning is inevitable once you’ve cut it, there are ways to delay the reaction.

This article gives you 6 tips to keep your avocados from turning brown.

Once avocados are cut, the PPO and a group of antioxidants called phenolic compounds found in the pulp are exposed to oxygen. The phenols then transition into pigment-creating compounds called quinones (1, 2).

Then, quinones and their byproducts go through several reactions, forming the brown pigment (1, 2).

This means that the enzymatic browning reaction is only triggered when PPO, phenolic compounds, and oxygen come in contact with one another. Thus, it can be prevented by removing oxygen from the cut surface (2).

Therefore, wrapping a cut avocado in plastic wrap or storing it in an airtight container may control oxygen exposure and delay browning.

Nevertheless, the browning can resume again you remove the avocado from the container and expose it to oxygen again (2).

Because PPO is crucial for controlling browning, targeting other factors that influence PPO’s activity may also help prevent browning (1).

Aside from oxygen, modifying pH levels is another helpful way to keep your avocados from browning.

Since PPO is active at pH levels between 6–7.5 but inactive below pH 3, one way to influence PPO is through applying acidulants — chemical compounds that help lower pH levels.

Acidulants, such as citric and ascorbic acid found in lemon juice, help lower the pH of avocados and decrease the enzymatic activity, keeping them from turning brown (1, 3).

Therefore, squeezing a little lemon juice on top of your cut avocado before storing it could help delay browning.

Evidence shows that onion extract may prevent enzymatic browning by inhibiting PPO activity (1).

Researchers believe that since PPO is a copper-containing enzyme, onion’s sulfuric compounds and their derivatives may interact with copper at the enzyme’s active site and hinder its activity (2).

In fact, compounds containing a sulfhydryl group may disrupt PPO-induced browning by up to 33% (2).

Therefore, storing your cut avocado with a sliced onion may also keep it from browning without affecting its flavor — as long as you make sure that the onion only remains in contact with the skin of the avocado and not the pulp.

Another way to keep your avocado from turning brown is by submerging it in coconut water.

Aside from limiting oxygen exposure, the antioxidant content of coconut water seems to play a role in delaying PPO’s enzymatic reaction (2).

However, you may not want to leave your avocado submerged in water for too long, as it can lose its firmness and become mushy. This might be a useful technique when you only need to store an avocado overnight.

As with lemon juice, coating your avocado with pineapple juice may keep it from turning brown.

In fact, two potential mechanisms explain the effect of pineapple juice on PPO.

On the on hand, evidence suggests that pineapple juice is comparable to sulfite — a widely used anti-browning agent that inhibits enzymatic browning (1).

While on the other hand, pineapple juice’s browning-inhibition properties may be a result of its antioxidant content (2).

Either way, brushing a bit of the juice on your avocado’s exposed pulp may help delay browning.

Adding a thin coat of honey to the surface of your cut avocado may also help delay avocado browning.

This is because honey acts as a barrier that helps limit contact with oxygen while inactivating the PPO enzyme at the same time (2).

Once more, there are two proposed mechanisms behind honey’s effect on PPO’s activity.

The first is that, similarly to onions, antioxidants in honey may interfere with copper in the PPO active site, which would block the enzyme’s activity (2).

The second potential reason: the presence of small peptides (amino acid chains) in honey reduces quinones, which would otherwise go through multiple reactions leading to the formation of the brown pigment (2).

Enzymatic browning creates a condition that significantly affects the quality of avocados by deteriorating their nutritional and sensory properties (1, 2).

In fact, it is one of the main reasons behind economic losses to both food producers and the food-processing industry (2).

However, avocados are safe to eat after they’ve turned brown. Just remove the browned surface, and you should still be able to enjoy the rest.

Nevertheless, if your avocado has an odd smell, it may indicate the presence of microbial deterioration, in which case you should discard it (4).

Avocado browning is a natural but undesired process that happens once you cut it due to the activity of an enzyme called polyphenol oxidase (PPO).

However, the fact that it is inevitable doesn’t mean that it can’t be delayed.

Some of the ways in which you could easily block the enzyme’s activity and prevent avocado browning are by wrapping it thoroughly, adding lemon or pineapple juice, or storing it with an onion.

While avocados are safe to eat after they’ve turned brown, their quality may be reduced. Be sure to discard them if they’ve started to smell bad.


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