2. Mechanical damage: apples that can be eaten in a short time will be damaged by squeezing, bumping and abrasion, and fruits damaged by external mechanical damage can be safely eaten. In this case, only some sensory changes affect the appearance (discoloration is due to the dissolution of fruit cytoplasm during collision, and colorless phenols become colored quinones), and most of them will not produce microbial toxins, so there is no risk for eating in a short time.

3. Frostbite at low temperature: It can be eaten for a short time. In a low temperature environment, the activity of superoxide dismutase in apples becomes low, so that free radicals in cells cannot be removed in time. Excessive accumulation will change the permeability of fruit cell membranes and destroy the structure of cells. On the other hand, low temperature environment will increase the activity of pectin esterase in fruit, decompose insoluble pectin substances in fruit, and also lead to fruit softening and rot. But this kind of frostbite is just "cell damage" and there is no microbial reproduction. Is relatively safe and can be eaten quickly.

4. mildew: you can't eat rotten fruit caused by your own mildew, even if you cut off the moldy part. As long as you can see the moldy fruit with naked eyes, it means that many germs have propagated and grown in the fruit, but the molded part on the surface of the mold mycelium has been cut off, and the mold lurking in the pulp can not be completely cut off. Therefore, even if the broken part of the apple is removed, the remaining good part is still inedible and harmful to the human body after eating.