The method of using heat to kill harmful microorganisms in food is not only an ancient method, but also an extremely important sterilization technology in modern times. In 1804, Frenchman Appert invented a method of bottling food and boiling it in boiling water for a period of time to preserve food for a long time. In the 1850s, the French Pasteur clarified the microbial spoilage mechanism of food, which laid a theoretical foundation for the development of sterilization technology. Food thermal sterilization can be divided into three types: low-temperature sterilization, high-temperature short-term sterilization and ultra-high temperature instantaneous sterilization.
(1) Low-temperature sterilization is also called pasteurization, and the sterilization conditions are 61°C to 63°C/30 minutes, or 72°C to 75°C/15 minutes to 20 minutes. Pasteurization technology is to fill and seal the food in the packaging container, and keep the temperature below 100 degrees Celsius for a certain period of time to kill the bacteria in the packaging container. Pasteurization can kill most pathogenic bacteria, but the ability to kill non-pathogenic spoilage bacteria and their spores is insufficient. If pasteurization is combined with other storage methods, such as refrigeration, freezing, deoxygenation, The packaging can meet the requirements of a certain shelf life.
Pasteurization technology is mainly used for the sterilization of citrus and apple juice beverages and foods, because the pH value of juice foods is below 4.5, there is no microbial growth, and the objects of sterilization are yeast, mold and lactobacillus. In addition, pasteurization is also used for the sterilization of jam, canned fruit in syrup, beer, canned pickled vegetables, pickles, etc. Pasteurization has reliable acid resistance for sealed acidic foods. For those low-acid foods that are not resistant to high-humidity treatment, as long as it does not affect consumption habits, it is often used to add acid or use microbial fermentation to produce acid to increase the pH value. Reduced to the range of acidic foods, low-temperature sterilization can be used to achieve the purpose of preserving food quality and storage resistance. This method takes a long time and is not suitable for heat-sensitive foods.
(2) High-temperature short-time sterilization (HTST): The sterilization conditions are 85°C to 90°C/3 minutes to 5 minutes, or 95°C/12 minutes, mainly used for aseptic milk and low-acid fruit juice drinks in low-temperature circulation For sterilization, a heat exchanger can be used to heat the liquid material to nearly 100 degrees Celsius in an instant, and then quickly cool it to room temperature. This method takes less time and has a better effect, which is conducive to product quality preservation. Mainly can kill yeast, mold, lactic acid bacteria and so on. These two methods have the characteristics of stable sterilization effect, simple operation, small investment in equipment, and long application history. They are still widely used in the sterilization of various canned food, beverages, wines, medicines, and dairy products.
(3) Ultra-high temperature instantaneous sterilization (UHT): It came out with the appearance of the Stork device in 1949, and then various types of ultra-high temperature sterilization devices appeared in the world. Ultra-high temperature short-time sterilization is to heat food to a high temperature (above 130 degrees Celsius) in an instant to achieve the purpose of sterilization. It can be divided into two methods: direct heating and indirect heating. The direct heating method is to use high-pressure steam to spray directly on the food, so that the food can be heated up at the fastest speed, reaching 140-160 degrees Celsius in a few seconds, maintaining it for a few seconds, then removing moisture in the vacuum chamber, and then cooling it with a sterile cooler. room temperature. The indirect heating method is based on the viscosity and particle size of the food, using plate heat exchangers, tube heat exchangers, and scraper heat exchangers.
The Plate Heat Exchanger is suitable for liquid food with a pulp content of no more than 1% to 3%. The tube heat exchanger has a wide range of products, and can process liquid foods such as concentrated fruit and vegetable juices with high pulp content. Tube heat exchangers can be used for products that will cause coking or clogging when using plate heat exchangers, but the viscosity is not enough to use scraped surface heat exchangers. The scraped surface heat exchanger is equipped with a rotator with blades, which scrapes on the heating surface to push the high-viscosity food forward to achieve the purpose of heat sterilization. The effect of ultra-high temperature instantaneous sterilization is very good, almost reaching or approaching the requirements of complete sterilization, and the sterilization time is short, the nutrients in the material are less destroyed, the food quality is almost unchanged, and the preservation rate of nutrients is over 92%. The efficiency is very high, and the effect is better than the other two thermal sterilization methods. The ultra-high temperature sterilization device combined with food aseptic packaging technology has developed rapidly at home and abroad, and now it has developed into a high-tech food sterilization technology. At present, this sterilization technology has been widely used in the sterilization of milk, soymilk, wine, fruit juice and various beverages. It can also be used to sterilize food after it is packed in bags and immersed in hot water at this temperature.
June 20, 2023
