Fresh fruits, vegetables, meat and fish are not enough to eat, and many people are reluctant to throw them away. Many people are used to pulling off a section of the fresh-keeping film to prevent the smell from running or help "keep fresh". However, what are the differences between those "all look the same" fresh-keeping films on the market? How can I use plastic wrap to keep fresh? Is it true that the "fresh-keeping film breeds bacteria" and "fresh-keeping film may cause cancer" on the Internet? This issue of food safety consumption tips asks researcher Zhong Kai, director of Kexin Food and Health Information Exchange Center, to reveal the secret. Shopping: Different materials and functions can not only isolate food and dust in the air, especially microorganisms "coveting food" to the maximum extent, but also maintain moderate oxygen permeability and moisture permeability, thus extending the food preservation period. The "scientific truth" of keeping food fresh with plastic wrap is actually so simple. The fresh-keeping film has different functions due to different materials. Zhong Kai told China Consumer News that the fresh-keeping films sold on the market can be divided into three categories: polyethylene (PE), polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC). PE (polyethylene) fresh-keeping film. Most of the fresh-keeping films sold in supermarkets are of this kind. It is waterproof and breathable, especially suitable for packaging fresh fruits and vegetables, frozen food, etc. However, it is precisely because of its good air permeability that it is not suitable for packaging food with high fat and easy to be destroyed by oxygen, such as cakes and cooked food. PE can be used for refrigerator preservation, but not for microwave heating. PVC (polyvinyl chloride) fresh-keeping film. It is commonly found in wholesale markets, farmers' markets and online. The advantages are good transparency, high viscosity and good elasticity. The disadvantage is that the thermal stability is poor. Plasticizers that are not friendly to human health will be released under high temperature. Therefore, meat, cooked food, fatty food, etc. cannot be packaged, especially not used under high temperature. At present, the fresh-keeping film is mainly used for packaging vegetables and some agricultural products at room temperature. PVDC (polyvinylidene chloride) fresh-keeping film. It has the characteristics of good freshness, firmness and easy adhesion, and can prevent water evaporation. It is mainly used for packaging and freshness preservation of meat, cooked food, ham and other foods. The most important thing is that because its temperature range is between - 60 and 140 ℃, it can be used not only for keeping fresh in refrigerators, but also for heating in microwave ovens. However, the cost of this kind of fresh-keeping film is high, the processing is difficult, and the market share is not high. Explanation: Compliant products ensure safety. "Freshness preservation film will not only accelerate the growth of bacteria, but also be more likely to cause cancer." This statement has always been the main reason why many people alienate the freshness preservation film. Zhong Kai explained that, as a product that can directly contact with food, the safety of qualified fresh-keeping film need not be worried. First of all, the role of plastic wrap is to inhibit rather than release or breed bacteria and other microorganisms. Bacteria and other microorganisms in food mostly come from the food itself. There are three reasons that lead to more bacteria and faster decay of foods covered with plastic wrap: first, food has been invaded by microorganisms before it is covered with plastic wrap; Second, the storage environment is not clean or the temperature is too high; Third, the fresh-keeping film itself is not properly stored or used, such as the storage environment is dusty and reused