As the Spring Festival approaches, all kinds of online and offline New Year's goods festivals have begun in succession. People have been shopping for fruits, meat, seafood and other New Year's goods to prepare for the festival. From the origin to the refrigerator at home, the food has gone through thousands of mountains and rivers, but it is still fresh; The fruits and vegetables stored early are still delicious in the Spring Festival... All of these depend on the food cold chain preservation technology that is constantly updated. Li Xihong, a professor at the School of Food Science and Engineering of Tianjin University of Science and Technology, said in an interview with the reporter of Science and Technology Daily that temperature control, moisture retention, gas and green preservation are the four major elements of food preservation, and almost all preservation technologies are carried out around these four aspects. The new fresh-keeping technology can not only keep the freshness of food, let more food go out of the country of origin and come to our table, but also be more safe, energy-saving and environmentally friendly. Modified atmosphere preservation technology: use gas to change the internal environment of food packaging This year, many consumers will find the words "modified atmosphere preservation box" printed on the packaging box when purchasing fresh products on e-commerce platforms. So, what is modified atmosphere preservation? In response, Li Xihong said that the modified atmosphere preservation technology is to use "preservation gas" to change the internal environment of food packaging, so as to achieve the purpose of slowing down the rate of food decay and extending the freshness of food. "The so-called 'fresh-keeping gas' is generally made by mixing carbon dioxide, oxygen and nitrogen according to the characteristics of the food, and filling it into the closed package where the food is located to replace the original air. Generally speaking, this can extend the fresh-keeping period of the food by more than 10%." Li Xihong said. Among the "fresh-keeping gases", carbon dioxide has the effect of inhibiting the growth and reproduction of most putrefactive bacteria and fungi. The higher the concentration of carbon dioxide, the less perishable the food is. However, the high concentration of carbon dioxide in the packaging for a long time will also affect the quality of food. "If the oxygen content in the confined space where the food is located is too low or there is no oxygen, the food will ferment and its taste will become sour." Li Xihong said that filling a small amount of oxygen into the food packaging bag can maintain the color and taste of fresh meat and fresh fruits and vegetables. In addition, oxygen can inhibit the respiration of organisms and also inhibit the growth of rotten bacteria and fungi. Nitrogen is an inert gas, which generally does not react with food and is not absorbed by food. In addition, the price of nitrogen is relatively cheap and the use cost is low. Therefore, in the "preservation gas", nitrogen is generally used as the filling gas. Nitrogen can form a protective film on the surface of food to achieve the purpose of bacteriostasis and preservation. It can not only maintain the taste and color of food, but also play a certain role in anti-extrusion. "The formula of 'fresh-keeping gas' will be adjusted according to different kinds of food," Li Xihong explained. The reporter learned that some brine cooked food sold on e-commerce platforms use a modified atmosphere preservation package that mixes carbon dioxide and nitrogen in the ratio of 3:7, while cold fresh meat mixes carbon dioxide and oxygen in the ratio of 2:8. If the gas mixing ratio changes, the preservation period may be unstable, and thus the preservation period may be shortened. "The use of modified atmosphere preservation packaging is very extensive, not only for the preservation of livestock, poultry, meat, fish, etc,