Why Does a Cut Apple Turn Brown?

Once it has been cut an apple trial grad-ually turn brown at the part w ere it cut Some people believe that the change is caused by touching the knife. In fact this is not true because it also happens when the apple is bitten. The real reason is due to two sub- stances called phenol and phenotic fer-ment in the apple cell. Before cutting,the phenol and phenotic ferment cannot meet so the colour of the apple does not change at all. However, after cutting, the two substances, meet and undergo a of changes, as a result the cut section grad ually turns brown.