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Principles Of Refrigeration And Freezing Methods
Apr 26, 2017

Low temperature treatment, as a means of inhibiting chemical reaction, enzyme reaction and inhibiting microbial growth, has been widely used in many fields.

In general, the lower the temperature, the slower the growth of microorganisms, to a certain temperature below the limits of all microbial activity is completely stopped, so you can use low temperature (Leng Dong) to control microbial growth. In the actual food preservation, often use 0 degrees Celsius or slightly higher temperature to refrigerate. Although it is impossible to completely inhibit the growth of microorganisms at such temperatures, the food can be kept in the original state for a long time. Because of its economical value, it is possible to say that cold storage is an excellent method of preservation for certain kinds of food.

1, microbial growth and environmental temperature

The physical and chemical conditions of microbial living environment can only be changed within a certain range. If beyond the scope of change, growth can not be carried out. In addition, the comprehensive environmental conditions, even in the range of possible growth in general, if the various environmental factors from microbial optimum growth, it can also decrease the microbial growth rate.

Environmental temperature is also one of the most important factors controlling microbial growth in this sense. Refrigerated to prevent food spoilage and deterioration of the environment, should make the temperature range is not suitable for most of the growth of spoilage microorganisms, so that a variety of food ingredients by microbial reaction activity caused to happen and this is the principle of low temperature preservation, the.

In general, microorganisms can grow in a wide range of temperatures, from the lowest -10 to 80. However, it is true that, from the point of view of various microorganisms, the range of temperature that can be grown is much narrower than that of a very large number of microorganisms. The microorganism with the optimum growth temperature of 25 to 45 DEG C is called thermophilic microorganism, and it is also a common microorganism around us. The microorganisms with the optimum growth temperature below 25 degrees C are called low temperature microorganisms, which are the important microorganisms that cause food deterioration during cold storage. The microorganism with the optimum temperature above 45 DEG C is a kind of common bacteria in soil.

2, the growth of microorganisms in low temperature environment

Most thermophilic bacteria have a certain degree of growth at a temperature of 0 DEG C or lower. But at this temperature, even if some microbes can grow, it's not a good temperature. They grow at a temperature of 15 DEG C or a maximum of 20. It is the microorganism that can grow under special low temperature, and its optimum temperature is about 10 degrees celsius. Therefore, at low temperature, the growth rate decreases with the decrease of temperature, and it is extremely slow under 0.

The results showed that the cell division time increased gradually from the optimum temperature. At about 0 DEG C, the rate of bacterial division is extremely slow.

3, the distribution of thermophilic microorganisms

The optimum temperature for the growth of microorganisms and the temperature range of metabolic activities are generally related to the temperature of the microbial living environment. Most of the fish that live in low water temperatures, mostly in the natural state, are mostly low - temperature - resistant microorganisms that grow well at 0 degrees C. Therefore, it is often found that the growth of these microorganisms can be found in the cold storage of fish, which are attached to these low temperature microorganisms, especially at temperatures around 0 degrees Celsius or slightly higher. For example, the number of viable bacteria increased with time in frozen fish at -2 C.

Thus, the possibility of fish and shellfish and other aquatic food psychrophilic microbial adhesion is relatively large. Although occasionally in agricultural psychrophilic microorganisms found in food, but attached to the meat, fruits and vegetables and other agricultural food bacteria on the most mesophilic type, so at low temperatures, these food spoilage and deterioration caused by yeast and filamentous bacteria than caused by bacteria more.

The reason that food storage at room temperature is often bad, caused by the Bacillus spores, even at 5 to 8 DEG C under low temperature, can also be spore germination after vegetative proliferation, but vegetative cells generated will slowly die at low temperature.

There are many kinds of filamentous bacteria or fungi that can grow at low temperature. Most of the Aspergillus and Penicillium in food can grow at the temperature of 10 degrees centigrade. At 5 or 0 DEG C, growth is limited, but there are still quite a few species that can grow. This type of filamentous bacteria in frozen food pollution, the largest proportion. The low temperature microorganism grows at the corresponding low temperature, because it is the cause of food spoilage and deterioration, so it must be paid attention to in order to prevent pollution and growth.

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