Why Do Apples Look Fresh on the Outside but Have Blackened Flesh Inside? Is It Due to Excess Preservatives?

When buying apples, many people encounter a situation where the fruit looks fresh and appetizing on the outside, but the flesh inside is blackened. This often leads to the assumption that the apples have been treated with preservatives.

Apples are a nutritious fruit that offers many health benefits. However, some people, especially when purchasing imported apples, find that while the skin looks fresh, plump, and shiny, the inside is discolored or even rotten. This raises suspicions about the use of chemicals or preservatives.

Regarding this matter, Dr. Vũ Thị Tần, lecturer at Hanoi University of Science and Technology, explained to VTC News that apples looking fresh on the outside but having damaged flesh inside is not caused by chemicals or preservatives. The phenomenon is usually due to harvesting, storage, and transportation processes before the apples reach consumers.

The blackened flesh could also be the result of Rhizopus oryzae fungus. This fungus can enter through the stem or bruised areas of the apple, then grow within the fruit’s tissue. It has been detected in South Korea. However, Dr. Tần noted that fungal contamination in apples is not common, and when it occurs, it is usually accompanied by visible mold on the surface and a foul odor.

In most cases, the darkening of apple flesh is related to cell oxidation. Damage to the cell membrane and structures such as mitochondria and vacuoles allows phenolic compounds to react with the enzyme polyphenol oxidase (PPO), producing melanin that turns the flesh brown. Over time, the texture becomes mushy and may develop an unpleasant odor.

Common causes of blackened apple flesh include:

• Storage at excessively low temperatures – which makes cell membranes brittle and prone to rupture, triggering internal oxidation while the skin remains intact.

• Overripe or long-harvested apples – which can decay internally while still looking fresh outside due to their thicker skin.

• Carbon dioxide (CO₂) toxicity – in high-CO₂ storage environments (such as sealed cold storage), which can cause intracellular stress, damaging cell structures and leading to blackened flesh.

To avoid buying such apples, inspect the stem and skin carefully for bruises or soft spots. Choose apples with smooth, firm, and glossy skin without signs of wilting.

Whenever possible, purchase apples from reputable stores with stable cold storage conditions. If you find damaged apples, you can request a refund or exchange, depending on the store’s policy.