Grades 3–5 · Materials & Matter
Why does a cut apple turn brown?
Inside an intact apple, cells keep many substances in separate places. Cutting or bruising damages some of those boundaries. Substances that were separated can mix, and oxygen from the air can reach exposed tissue more easily.
In the diagramCell damage can enable browning reactionsSeparated cell contentsExposed, damaged tissueoxygenEnzymes speed reactions; brown products can formColor alone is not a complete freshness or food-safety test.
An enzyme already present in the apple helps certain compounds react with oxygen. An enzyme is a biological helper that speeds a reaction. The resulting products can go through further changes that produce brown-colored material.
The brown color is therefore a sign of chemical changes at the exposed surface, rather than dirt settling from the air. Different apple varieties and conditions can produce different speeds of browning because their materials and reaction conditions differ.
Changing temperature, acidity or oxygen access can affect this process, which is one reason food production pays attention to those conditions. This explanation concerns one kind of color change. Browning by itself is not a complete test of freshness, spoilage or food safety.
About this explanation
Starting knowledge: Know that foods contain cells and that substances can react to form different substances.
Sources
- Pennsylvania State University Extension — Preserving Color and Preventing Browning of Foods