Simplifier

When you cut an apple, like the one on the left in the picture, the inside gets exposed to the air. Think of it like the apple taking a breath. Inside the apple, there are natural things that react with the air, and this reaction causes the apple's flesh to change color, usually turning a yellowish-orange or brown. This is why the apple on the left looks discolored in the middle, while the one on the right still looks fresh and light-colored. This color change is mostly what we call "oxidation," which is just a fancy way of saying it's reacting with oxygen from the air. While the biggest change you see is the color, sometimes the texture can also get a little softer or mushier if it sits out for a very long time. So, the apple on the left has been exposed to air for a while, causing it to "rust" a bit on the inside and change color. The apple on the right looks like it was just cut, or maybe it was treated to keep it from changing color so quickly.

Culinary Physics Expert

Upon slicing, apples undergo distinct physical and chemical transformations. The most prominent change observed in the left apple half is enzymatic browning, a direct consequence of oxidation. When the cellular structure is disrupted by cutting, enzymes like polyphenol oxidase (PPO) are released and come into contact with phenolic compounds and atmospheric oxygen. This interaction catalyzes the oxidation of phenolics into quinones, which then polymerize to form dark melanin pigments, resulting in the visible yellowish-orange discoloration, particularly concentrated around the core. Beyond the chemical changes, slicing also initiates alterations in texture. The mechanical action of the knife ruptures cell walls, immediately compromising the turgor pressure that contributes to the apple's crispness. This cellular damage leads to the release of intracellular fluids and an increased surface area for moisture loss. Over time, dehydration of the exposed surface can further contribute to a softening or loss of firmness, though this specific textural degradation is less immediately evident in the provided image compared to the browning.

Plant Physiologist

Upon slicing, apples undergo rapid biochemical transformations, most notably enzymatic browning. This process is initiated by the disruption of cellular compartmentalization, which allows polyphenol oxidase (PPO) enzymes, typically sequestered in plastids, to come into contact with phenolic compounds stored in the vacuole. In the presence of atmospheric oxygen, PPO catalyzes the oxidation of these colorless phenolic substrates to highly reactive quinones. These quinones then spontaneously polymerize to form brown-colored melanin pigments, resulting in the visible discoloration observed on the cut surface. The rate and intensity of this oxidative browning are influenced by factors such as the apple cultivar's PPO activity and phenolic content, as well as environmental conditions like temperature and oxygen availability. Concurrently, slicing also initiates alterations in texture. The mechanical wounding activates or releases endogenous cell wall-degrading enzymes, such as pectinases and cellulases. These enzymes begin to hydrolyze the structural polysaccharides of the cell walls, leading to a gradual breakdown of tissue integrity. This enzymatic degradation contributes to a progressive softening of the apple flesh, diminishing its characteristic crispness and turgor over time.