2. Cryopreservation: Low temperature can weaken the general chemical reaction in food, reduce the activity of enzymes and inhibit the reproduction of microorganisms, while below freezing point, general microorganisms stop growing;
3. High temperature preservation: After high temperature treatment, most microorganisms in food are killed and enzymes are destroyed. Other preservation methods such as sealing, vacuum and cooling must be adopted to preserve food for a long time. There are two commonly used temperature categories: pasteurization and high temperature sterilization;
4. Dry preservation: reduce the moisture content of food below a certain level and inhibit the growth of microorganisms that can cause food corruption and food poisoning;
5. Improving osmotic pressure to keep fresh: the practical application is mainly salt pickling and sugar pickling;
6. Irradiation preservation: refers to the treatment of food or food raw materials by artificially controlled radiant energy in order to achieve the purpose of sterilization, disinfestation and inhibition of germination.