Take apple as an example. If it is placed in the air for a short time and has only slight discoloration, it can be eaten. We can cut off the discoloration on the food and eat the non oxidized part. But if the food has been stored in the air for a long time and has gone bad, it's best not to eat it. Can we eat oxidized food? Usually, if we cut some fruits and vegetables and place them under the air, it is easy to have oxidation reaction. At this time, if the food is placed under the air for a long time and the surface is only slightly discolored, we can continue to eat.
Take apples as an example. When the surface of our apples changes color, if we mind, we can cut off the discolored part of the apple surface and eat the part without oxidation. But if these foods are put in the air for too long and have gone bad, they can't be eaten.
If we don't want the cut fruits to oxidize so quickly, we can put them in a bowl and seal them with a fresh-keeping bag, so that we can separate the food from the air and it won't oxidize so quickly.