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The chemistry of a browning apple

Slice an apple open and leave it on the counter, and the pale flesh soon turns rusty brown. Cutting the fruit breaks open plant cells, allowing an enzyme called polyphenol oxidase to react with oxygen in the air and phenolic compounds in the apple, a chemical defense mechanism that changes the fruit's appearance and flavor.

3–5 min

Questions you could explore

  • What changes when the tissue is cut?
  • Why is color alone an incomplete test of food safety?

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Food

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How does milk become yogurt?

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Food

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3–5 min

Keeping oil and water together in mayonnaise

Food3–5 minPour oil and water into a jar, shake them hard, and they will quickly separate back into two layers. Yet mayonnaise stays a thick, stable sauce because vigorous whisking breaks the oil into microscopic droplets, while emulsifiers in the egg yolk coat those droplets and stop them from recombining.

The chemistry of a browning apple | Speech Topic | speaking.app