There are _ _ _ _ ways to keep food fresh, and the principle of preventing food from spoilage is _ _ _ _.

Because all kinds of bacteria, fungi and other microorganisms come into contact with food and use the organic matter on food to develop and reproduce, during this period, a large number of growth metabolites will be produced, resulting in various flavors, such as acid and odor. Therefore, food spoilage is caused by the growth and mass reproduction of microorganisms. According to the causes of food spoilage, food preservation should try to kill or inhibit the growth and mass reproduction of microorganisms. Traditional food preservation methods include salting, sugaring, drying and soaking in wine. Modern storage methods mainly include canning, dehydration, freezing, vacuum packaging and adding preservatives. The main cause of food corruption is the reproduction of microorganisms, so the basic principle of food preservation is to kill or inhibit the growth and reproduction of microorganisms in food. Therefore, food preservation methods include canning, dehydration, freezing and vacuum packaging. The principle of preventing food from spoilage is as far as possible.

So the answer is: canning, dehydration, freezing, vacuum packaging; Try to kill or inhibit the growth and reproduction of microorganisms.