In the past 100 years, people have studied the use of ultrasonic, microwave, high pressure, irradiation and other means to disinfect milk , but the actual application is only a method of "heat treatment". Pasteurization : Development of heat treatment milk processing science and technology, began in the mid-19th century founder of microbiology, Louis Pasteur discovered the existence of the milk when microorganisms. He found that heating not only kills the vitality of killing microorganisms but also destroys the flavor of milk , so he founded pasteurization. Sterilization formula is: 63 ℃, keeping 30min. The purpose is to ensure that all pathogenic bacteria in the milk are killed to ensure safe drinking , and that the inherent flavor and sensory of the milk can be largely preserved. Later, a new pasteurization method was developed , that is , the continuous pasteurization process at 72 ° C / 15 s became mature and generally accepted. In order to distinguish, then Pasteur proposed sterilization process is called "low temperature long (LTLT) pasteurization", and the new technology is called "high-temperature short-time (HTST) pasteurization"; Product They are all known as "pasteurized milk." Later, some people did in-depth research and came up with a series of different temperature and time combinations , such as today's internationally recognized 90 °C / 0 · 5s , 94 °C / 0 · 1s , 96 °C / 0 · 05s , 100 ℃ / 0 · 01s and the like, they belong to an equivalent "pasteurization", but the holding time were less 1s, the principle of the conventional flow rate control flow can not reach the time required control accuracy, so have borrowed "steam injection "Flash" phenomenon caused by direct heating of milk or " infusion " to precisely control the holding time , thus enjoying another common name "High Thermal Instant Pasteurization (HHST) " . After pasteurization, the microorganisms remaining in the milk are mainly heat-resistant non-pathogenic bacteria . The activity of some enzymes has not been completely passivated . After a certain period of time, the activity will continue to deteriorate during the storage period. Therefore, pasteurized processed products generally do not have to be expensive aseptic filling, but be careful to prevent the product of "secondary pollution", the control value to "approximate number of coliform zui" expressed as an index shall not exceed the limit . Therefore, even when food cold (4 ~ 10 ℃) conditions, the shelf life of the finished product, only a few days. How to further reduce the storage conditions of milk on the basis of Pasteur, dairy science and technology has become the goal. Modern technological development Although the market is not optimistic about "maintaining sterilized milk" , it has attracted the interest of some researchers. On the basis of a large number of researchers were studies, first in the 1960s to achieve a breakthrough in two basic theories of heat-treated milk. *The kinetic principle of the thermal stability of the milk protein system. The second is the difference in the rate of change between the two effects of bactericidal action and chemical reaction caused by different heat treatment temperature change rates. In the mid- 20th century , ultra-high temperature transient sterilization (UHT) technology entered commercial applications with the maturity of direct heating and indirect heating equipment. And by the Dutch Stoke (StorkBrabantB · V ·), British APV companies to develop indirect method of heating the sleeve-type sterilizer, gained commercial success in the competition in the 1970s and 1990s. In the early 1980s, the International Dairy Federation (IDF) issued a series of documents relating to UHT technology and products, this new technology marks the zui final maturity. It is worth noting, IDF under the definition of normal to mention two aspects of the technical requirements when shelf life of at least six months of UHT products, one from "canned food" hygiene introduction of "commercial sterility" concept, which has to China's dairy industry generally accepts and writes national standards. The other is the “improved turbidity identification†in physics and chemistry , which has not been discussed much in China. This indicator is actually set to prevent excessive heating from destroying the nutrients of the milk and possibly creating new unidentified substances. The objective results of the identification tell us that for milk treated with UHT technology , the degree of denaturation of the protein must be controlled at an appropriate location between the pasteurized milk and the sterilized milk. UHT milk products from the color, smell, taste and nutrient retention and generation of unknown material point of view, compared to pasteurized milk is significantly different. Therefore, in mature dairy markets it is difficult to win a large share, but the lack of milk in the cold chain is not universal and local, as well as some special occasions "fast-paced" life, was favored. In view of the unsatisfactory UHT products , dairy technicians are still researching and making new progress. This is the “extended shelf life milk†that has been praised by foreign counterparts as “a new generation of sterilized milkâ€. It is a direct heating method that uses a heat transfer rate faster than about 100 times that of the indirect heating method . The temperature of the raw milk is quickly raised from 75 °C to the temperature required for sterilization at 133 °C in 0 · 2 s . Nutrients not conducive to rapid heating chemical reaction; after precisely controlled incubation time 0 · 5s, followed by using a "flash" means that the pressure is released so that the milk temperature is decreased rapidly to 0 · 2s 75 ℃, while evaporating It was originally brought into the milk by high temperature and high pressure steam. Moisture in the water. In the application ESL, if you want to control the degree of nutrient retention milk and pasteurized milk equivalent, then the degree of killing of microorganisms can be more thorough than pasteurized milk; not yet reached the degree of sterilization, but in the same cold Under the chain condition, the shelf life of the product can be extended , generally 20~45d; the chemical reaction caused by sterilization is significantly reduced. IDF discussed the ESL product technology in 2002 , marking the birth of another new technology. Prior to this , the direct heating method has been applied in the field of milk powder production and achieved good results. Due to the low material in the whole process of heat intensity, reflected in the final product of milk zui functional parameters were significantly improved, the fundamental reason is the degree of protein denaturation of milk has been effectively controlled, is called "cold milk" on business High-end products. After entering the 21st century , almost all production lines of formula milk powder ( especially infant milk powder ) produced abroad ( excluding those located in China ) have been transformed into direct heating method , and most of the water vapor used comes from the use of concentrated milk. in the "secondary steam" of the milk itself, the "heat pump" after warming reuse. It not only avoids the trouble of water treatment , but also saves energy . Unfortunately, there is no application of such technology in China so far. 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