Sterilization is a very important link in the food processing process, which directly affects the quality and shelf life of flexible packaged food. The sterilization methods used in food flexible packaging mainly include thermal sterilization and non-thermal sterilization. The main purpose of thermal sterilization is to kill microorganisms that can cause food spoilage and deterioration during the normal shelf life of the food. Generally, the heat treatment strength required to achieve sterilization is sufficient to inactivate the enzyme activity in food. The following mainly expands some specific heat sterilization methods of food flexible packaging .
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Heat sterilization
It is a form of heat treatment with the main purpose of killing microorganisms. It is mainly divided into pasteurization. The methods of sterilization are usually divided by pressure, temperature, time, heating medium and equipment. The pressure can be divided into normal pressure sterilization and pressurization Sterilization; the heating medium for sterilization can be hot water, steam, a mixture of steam and air, and flame.
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1 Atmospheric humid heat sterilization
Mainly uses water (also with steam) as the heating medium, and the sterilization temperature is 100 ℃ or less. It is used for sterilization of acidic foods or low-acid foods with low sterilization requirements. Canned sterilization at atmospheric pressure is suitable for metal cans, glass bottles and meat food flexible packaging containers. There are intermittent and continuous sterilization equipment.
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2 High-pressure steam sterilization
Using saturated steam as the heating medium, the can is in saturated steam during sterilization, and the sterilization temperature is higher than 100 ° C, which is used for sterilization of low-acid food. The air in the sterilization equipment must be exhausted during sterilization, which is conducive to keeping the temperature consistent. At higher sterilization temperatures, air back-pressure cooling is generally used for cooling. There are intermittent and continuous sterilization equipment, and there are static and rotary food flexible packaging in the sterilization equipment. Rotary sterilization equipment can shorten the sterilization time.
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3 High pressure water sterilization
The water under air pressure is used as the heating medium, and the sterilization temperature is higher than 100 ℃. It is mainly used for sterilization of low acid cans with glass bottles and soft materials as containers. During sterilization (including cooling), the cans are immersed in water to make the heat transfer uniform, and to prevent damage to the container due to too much pressure difference between the inside and outside of the tank or excessive temperature changes. It is necessary to maintain a good circulation of air and water during sterilization to make the temperature uniform. The sterilization equipment is mainly intermittent, but the can can keep rotating during sterilization. When sterilizing soft cans, special trays (racks) are required to place food soft packaging to facilitate the circulation of the heating medium.
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4 Air pressurized steam sterilization
Steam is used as the heating medium, and compressed air is added to the sterilization equipment to increase the pressure outside the tank and reduce the pressure difference between the inside and outside of the tank. Mainly used for high temperature sterilization of glass bottles and soft cans. The sterilization temperature is above 100 ℃, and the sterilization equipment is intermittent. The control requirements are strict, otherwise it is easy to cause uneven temperature distribution in the sterilization equipment during sterilization.
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5 heat-sealing sterilization canning
It is to heat treat the food before canning, and then seal the food while it is hot. Use the residual heat of the food to complete the sterilization or secondary sterilization of the can after sealing. After reaching the sterilization requirements, cool the can. It is mainly used for the sterilization of acid foods such as juice sauce. The sterilization equipment mostly uses the tube type or the slice type, which requires high cleanness and sterility of the canned container. After sealing, the cans are often turned upside down to ensure the sterilization of the can lid.
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6 Pre-sterilized aseptic filling
It is to make the food meet the sterilization requirements in the pre-sterilization process, then cool to normal temperature, put it in a sterile container after sterilization and seal it (sealing). Mostly used for sterilization of liquid and semi-liquid foods. The pre-sterilization is completed in the heat exchanger and the time is short. Aseptic canning can be done in aseptic packaging equipment or systems and is a continuous high-temperature short-term or ultra-high-temperature instant sterilization method. It is suitable for food flexible packaging materials and metal and plastic containers.
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