Problems and development of microwave food packaging
microwave food refers to the application of modern processing technology, the use of scientific proportion and combination of food raw materials, pre processed into food suitable for microwave oven heating or modulation, easy to eat
microwave food can be divided into three categories,
the first category is cooked food that can be stored at room temperature after microwave sterilization,
the second category is products that are frozen and refrigerated after being prepared with selected materials. At that time, the time for exhibitors to enter and withdraw from the museum will also be extended. When used, just put the food into the microwave oven to thaw and heat it, and you can eat it
the third category is snack foods.
compared with traditional heated food, microwave heating is difficult to achieve the brittleness and browning produced during frying and baking. At present, the methods to solve this problem are mainly concentrated in three categories: first, starting from the heating device, install an electric oven in the microwave oven for baking; Second, starting with packaging materials, thin coating materials are used as packaging materials for microwave food, such as evaporation of aluminum layer with appropriate thickness on PET film, tin oxide coated glass and other technologies. Such materials can reach a high temperature of about 250 ℃ in a few seconds in the microwave field, and can be used as a second heating source to produce a burnt yellow color on the food surface; Third, the edible coating is directly coated on the food surface. This kind of coating is mainly a batter system composed of water, flour, bread crumbs, starch, chemical bulking agent, egg white and other seasonings, and the coating is edible, film-forming and water holding properties are good. Combined with bulking agent, it can produce the effect of crispy outside and soft inside. In addition, the pigment and browning agent contained in the coating can produce attractive color on the food surface. The requirements for selecting microwave packaging materials mainly include: ① packaging materials should meet health standards. ② The material has low dielectric coefficient and good microwave penetration. ③ It has heat resistance. The degree of heat resistance needs to be greater than the temperature of food after heating, and it can withstand rapid temperature changes. ④ It has cold resistance. Because microwave food needs low temperature circulation, it needs to withstand a temperature of 20 ℃. ⑤ Resistant to oil, water, acid and alkali. ⑥ Convenient and cheap, in line with environmental protection requirements. Glass, ceramics, paper, plastics, metals and nonmetals, as well as the composites of these materials, can be used as microwave food packaging materials. Microwave food packaging can be divided into outer packaging and inner packaging. The outer packaging is usually a packaging carton printed with exquisite patterns and instructions to attract consumers; The inner packaging refers to the disc or box plastic container, which is convenient for direct processing in the microwave oven. The microwave food packaging we studied is mainly inner packaging. According to the different mechanism between materials and microwave heating, microwave food packaging materials can be divided into three categories: Microwave penetrating materials, microwave absorbing materials and microwave reflecting materials. Glass, plastic and paperboard are excellent microwave penetrating materials. Therefore, at present, most microwave food packaging containers are made of these materials. Among them, plastic products are more widely used because of their lightness, durability and good comprehensive performance.
the most commonly used microwave penetrating material in microwave food packaging is plastic containers, such as filled polypropylene containers. Talc powder is mostly used as the filler, because talc powder has the dual functions of improving heat resistance and rigidity, and shortening the production cycle, thereby reducing the container cost. The amount of talc powder is generally about 30%, and the heat resistance of the container can reach more than 130 ℃; Some kinds of filled polypropylene microwave containers have a filler content of about 50%, which can withstand high temperature of 140 ℃ and low temperature of -30 ℃. Another feature of the filled polypropylene container is that the waste is easy to burn. The addition of a large number of fillers makes the combustion heat of plastic increase. The experimental speed is 0 (3) 0 cycles/min (can be set), and the tacit speed: 20 times/min decreases greatly, only about 5000 kcal/kg, which is similar to the combustion value of wood, so it is not easy to damage the incinerator during combustion. The disadvantage of this kind of container is that it is opaque, and the objects contained in the container cannot be observed through the container. Polyester container is another kind of clamp wave food packaging container, such as Tianhui and sans. The practical polyester microwave oven container is a thermoformed container made of crystalline polyethylene terephthalate sheet - CPET container. The highest heat-resistant temperature of this container is 230 ℃, which is extremely rare in common plastic products. CPET has the advantages of oil resistance, chemical resistance, low temperature resistance, health and safety, and easy recycling of waste. It is a very ideal plastic container for microwave ovens, but it is technically difficult to make this product and the cost is high. Microwave absorbing materials are also commonly used microwave packaging materials, which are called microwave sensing materials. The commonly used thin coating material is to deposit some metal particles (such as aluminum) on the surface of plastic film (such as PET) by thermal evaporation or spray plating (the thickness is about 10nm), and then composite this plastic film with kraft paper with thermal stability by lamination. One of the most important properties of this material is its surface resistance. When the thickness of the metal coating is very large, its surface resistance is zero, and all the microwave energy transmitted to the coating surface is reflected back. With the decrease of the thickness of the metal coating, the surface resistance and the amount of microwave absorbed gradually increase. When the coating thickness is optimal, it can absorb 50% of microwave energy. This kind of film can reach a high temperature of about 250 ℃ in a few seconds in the microwave field. It can be used as a heating plate to produce a burnt yellow color on the surface of food. The development trend of microwave food will still focus on how to maintain the inherent flavor and taste of food, and develop new processing technologies and processes. Due to the sharp rise in temperature caused by microwave heating, the essence flavor substances in the microwave food whose degradation products are CO2 and H2O evaporate, and the flavor and taste of the food are worse than those of the stir fried dishes. Therefore, people are studying and trying out the flavor retention agent that can maintain the essence unchanged for a long time, so as to improve the heat resistance. Microencapsulation technology can also be used to protect essence. In recent years, in order to keep the color, aroma, taste and shape of microwave food the same as that of stir fried dishes, all manufacturers have made great efforts in the water absorption, oil absorption and odor removal of packaging materials. At the same time, the thermal effect of microwave itself is used to make the products have the crispness of other foods, which looks yellow and crispy to enhance appetite and prevent uneven heating. In order to be convenient to use, various forms of packaging methods such as packaging containers and tableware, packaging materials with steam removal function, paper trays, paper cups and so on are flexibly used for frozen food
consider cooking bags, plastic and paper containers without aluminum foil in terms of preventing metal sparks. Multilayer composites will become the mainstream of microwave packaging in the future, such as unsaturated polyester, glass fiber and other materials, which can meet the requirements of different grades of microwave food in different circulation environments
in addition, plastic coated ceramics and glass also have a promising future. Glass packaging containers have been specially treated, which greatly improves the crushing resistance of containers and will become one of the popular packaging containers for microwave food. In recent years, researchers have developed a new type of high barrier packaging material - sixo and other non-metallic oxide coating composite packaging materials. In addition to the barrier performance comparable to aluminum-plastic composites, this material also has the advantages of good microwave permeability, high temperature resistance, transparency, and little influence by ambient temperature and humidity. Especially in terms of commodity fragrance preservation, the effect is the same as glass bottle packaging, long-term storage or high-temperature treatment, It will not produce peculiar smell and is suitable as a kind of packaging material for microwave heated food. In addition, according to the information, the microwave cooking indicator that has been successfully developed can be installed outside the microwave food package. When the food is cooked, its temperature indicator will change color, and consumers can see it at a glance. In a word, the microwave food industry is basically in its infancy in China. As long as we firmly grasp the new trend of market demand and vigorously develop, research and produce new microwave food products that conform to domestic and foreign consumption habits, we will certainly achieve a lot