Fruits Containing Polyphenol Oxidase and the Science Behind Browning

December 27, 2025 •

4 min read

According to research, polyphenol oxidase (PPO) is widely distributed in the plant kingdom, causing enzymatic browning in damaged fruits and vegetables. Several common fruits contain polyphenol oxidase, which becomes active when the plant tissue is cut, bruised, or damaged, exposing the enzyme and phenolic compounds to oxygen.

Quick Summary

An exploration of common fruits containing polyphenol oxidase and the mechanism behind enzymatic browning. Provides details on fruits with high and low PPO activity, methods for inhibition, and the significance of this enzyme in food science and plant defense.

Key Points

Common Fruits: Apples, bananas, and avocados are prime examples of fruits with high polyphenol oxidase (PPO) activity, which is responsible for rapid browning upon cutting or bruising.
Browning Mechanism: PPO reacts with oxygen and phenolic compounds in damaged fruit tissue to produce melanin, a brown pigment.
Low PPO Fruits: Certain fruits, such as pineapples, oranges, and some berries, have very low PPO activity and therefore do not brown easily.
Inhibition Methods: The browning process can be inhibited by reducing the pH with acid (like lemon juice), denaturing the enzyme with heat, or limiting oxygen exposure.
Smoothie Considerations: Combining high-PPO fruits like bananas with low-PPO, polyphenol-rich fruits (like berries) can significantly degrade the beneficial flavanols in the berries.
Applications: Beyond fresh fruit browning, PPO plays a role in the processing of products like black tea, coffee, and prunes, where the browning is desirable.

Understanding Polyphenol Oxidase

Polyphenol oxidase (PPO) is an enzyme that catalyzes the oxidation of phenolic compounds into quinones, which then polymerize to form brown, black, or red pigments called melanins. This process is known as enzymatic browning and is a major cause of quality loss in fruits and vegetables after harvesting, bruising, or cutting. PPO and phenolic compounds are naturally separated within the plant's cells, but when the cells are damaged, the contents mix and react with oxygen in the air. The activity and effect of PPO vary widely across different fruits and even between different cultivars of the same fruit.

Common Fruits with High PPO Activity

Certain fruits are notorious for their rapid browning due to high levels of polyphenol oxidase and phenolic substrates. These include a variety of popular produce items:

Apples: One of the most well-known examples of PPO activity, apples turn brown quickly after being sliced. The degree of browning can vary significantly depending on the apple variety.
Bananas: High PPO activity is responsible for the darkening of banana peels and pulp, especially when bruised or overripe. Researchers have found that blending bananas in smoothies can significantly degrade the phenolic compounds from other low-PPO fruits mixed in.
Avocados: When an avocado is sliced and exposed to air, the PPO causes a rapid browning of its green flesh, which is a key indicator of the enzyme's presence.
Pears: Similar to apples, pears are susceptible to enzymatic browning after cutting or bruising.
Apricots: As a climacteric fruit, apricots have PPO that can activate during storage, contributing to browning.
Cherries: Both sweet and sour cherries contain PPO and are susceptible to browning, particularly after storage or processing.

Fruits with Lower or Manipulated PPO Activity

Not all fruits exhibit high PPO activity. Some naturally have lower levels, while others have been genetically engineered to suppress the enzyme's function.

Berries: While berries contain high levels of phenolic compounds, some, like certain berries used in smoothies, have low PPO activity compared to bananas. This is why combining them with high-PPO fruits in a smoothie can be detrimental to the berry's flavanol content.
Pineapple and Oranges: These citrus fruits possess naturally low PPO activity, which is why they don't brown when cut.
Arctic Apples: An example of gene silencing technology, these apples are engineered to have very low PPO activity, preventing them from browning after being sliced.
Passion Fruit: Research on tropical fruits has shown that some varieties, including passion fruit, have notably low PPO activity.

Methods for Inhibiting Enzymatic Browning

Preventing or slowing the browning process is crucial in food processing and preparation. Several methods can be used to inhibit PPO activity:

Lowering the pH: PPO is most active at neutral pH and its activity decreases in acidic environments. Squeezing lemon or pineapple juice, which are acidic, onto cut fruit is a common method to prevent browning.
Heat Treatment: High temperatures can denature the PPO enzyme, permanently inactivating it. This is why cooked fruits do not brown. Blanching, a quick heating process, can be used to prevent browning in cut fruit before further processing.
Reducing Oxygen Exposure: Oxygen is a necessary reactant for PPO to function. Submerging cut fruit in water or covering it with an airtight wrap can prevent oxygen from reaching the surface and initiating the reaction.
Use of Chemical Inhibitors: Compounds like L-cysteine and glutathione can be effective inhibitors of PPO. Honey also contains a peptide compound that can inhibit PPO activity.
Use of Antioxidants: Vitamin C (ascorbic acid) is a powerful antioxidant that reduces the quinones produced by PPO back to their colorless phenolic form, effectively stopping the browning reaction.

Comparison of High vs. Low PPO Fruits


Feature	High PPO Fruits (e.g., Apple, Banana)	Low PPO Fruits (e.g., Pineapple, Orange)
Browning Reaction	Rapid and noticeable browning upon cutting or bruising due to oxidation of phenols.	Very slow or negligible browning because of low enzyme activity.
Cellular Compartmentalization	PPO and phenolic compounds are segregated but readily mix when tissue is damaged.	Lower concentrations of the PPO enzyme are present, meaning less reaction occurs upon damage.
Nutrient Stability in Blends	Can cause significant degradation of polyphenols from other low-PPO fruits when blended.	Good for preserving the antioxidant flavanols and other polyphenols from other ingredients in smoothies.
Preservation Methods	Requires intervention (acidification, heating) to prevent aesthetic and nutritional decay.	Requires less treatment to maintain appearance and nutritional quality after cutting.
Genetic Modification	Some varieties, like Arctic apples, have been genetically modified to reduce PPO activity.	No significant need for genetic modification regarding PPO for these fruits.

Conclusion

The presence of polyphenol oxidase in many fruits is a natural biological process that serves various functions, including plant defense. However, the resulting enzymatic browning can be a significant issue for consumers and the food industry, impacting visual appeal and nutritional value. Fruits like apples, bananas, and avocados are high in PPO, while citrus fruits and some berries have low PPO activity. By understanding which fruits contain polyphenol oxidase, and how its activity is triggered and controlled, we can apply simple techniques like adding lemon juice or heat treatment to preserve the freshness and quality of our food. This knowledge is a cornerstone of food science and provides practical benefits for everyday cooking and food preparation.

Frequently Asked Questions

Fruits with high levels of PPO and phenolic compounds, such as apples, bananas, and avocados, tend to brown the fastest. The speed of the reaction depends on factors like the fruit's ripeness, temperature, and exposure to oxygen.

Yes, it is generally safe to eat fruit that has browned due to PPO. The browning is a chemical reaction that changes the fruit's appearance and sometimes its texture and flavor, but it does not make the fruit unsafe to consume.

You can prevent browning by treating the apple slices with an acidic substance like lemon juice or honey water, which lowers the pH and inhibits PPO activity. You can also reduce oxygen exposure by storing the slices in an airtight container.

No, simply mixing low-PPO fruits with high-PPO fruits won't prevent browning. In fact, research shows that blending high-PPO fruits like bananas with polyphenol-rich but low-PPO fruits (e.g., berries) can cause significant degradation of the beneficial polyphenols.

Yes, cooking or heating fruits and vegetables to a high enough temperature will denature and inactivate the PPO enzyme, permanently stopping the browning process.

PPO is widely distributed in the plant kingdom, but not all fruits have equally high or detectable levels of the enzyme. Fruits like pineapple, oranges, and passion fruit contain very low PPO activity, and some plants like Arabidopsis lack it entirely.

In plants, PPO plays several roles, including part of the defense mechanism against pests and pathogens. When plant tissue is damaged, PPO-induced browning can make the plant less palatable or toxic to herbivores.