Why do citrus prevent apples from turning brown?
The browning of a cut apple is caused by an enzyme present in apple cells. When the cells are damaged, the enzyme leaks out, reacts with oxygen and starts digesting the apple, turning it brown. Adding citrus juice to the apple’s cut surface will ‘denature’ the enzyme. By denature, I mean that the shape of the enzyme changes which destroys the enzyme’s ability to digest or breakdown the apple. Enzymes only work within a specific range of pH (acidity-alkalinity). Experimentally, you could try putting water on instead of citrus juice or clear vinegar or soap solution and see what differences with the speed of browning you observe. Measure the pH of the different substances you use.
