Factors that influence the sterilization effect of culture medium.
The sterilization of the culture medium is thorough, and the factors affecting it are many. Besides the type and quantity of the bacteria in the medium, the degree of sterilization temperature and the length of time are also dependent on:
1. Retention of nutrients.
When the bacteria are killed, the nutrients in the medium are also destroyed, especially amino acids and vitamins. As in the 121 ℃, 20 min, there are 59% of lysine and arginine and other basic amino acid are destroyed, methionine and tryptophan are quite a number of damaged. Under the action of heat, certain nutrients may react with each other due to heat, resulting in a change in the number of original nutrients in the medium, thereby affecting the quality of the medium.
2. Heat resistance of microorganisms.
The thermal resistance of bacterial spores is large, and the time required for sterilization depends on the time required to reduce the bacterial spores to the specified number.
3. The pH
The pH value has great influence on the heat resistance of microorganisms. When the pH value is between 6.0 and 8.0, microorganism is the most difficult to die. When pH<6.0, microorganisms are relatively easy to die. At this point, H+ can easily infiltrate into the cells of microorganisms, thus changing the physiological response of the cells and causing them to die. So the lower the pH of the medium, the shorter the time.
4. Medium composition.
High concentrations of organic matter, such as fats, sugars and proteins, can be encapsulated in the surrounding form of the cell and affect the conduction of heat. The high concentration of salt and pigment weakens its heat resistance and is easy to sterilize. Such as e. coli in water heated to 60-65 ℃ was killed, in 10% sugar solution to 70 ℃ heat 4 to 6 minutes before death, in 30% sugar solution need 30 minutes before death. When had better choose a more sugar content in 115 ℃, 30 minutes; General medium can choose 121 ℃ for 20 minutes.
5. The bubble
The air in the bubble forms an insulating layer that makes it difficult to penetrate and kill the bacteria.
Small particles, easy to sterilize, large particles, difficult to sterilize. For medium containing a small amount of large particles and coarse fiber, the method of coarse filtration (which should not affect the quality of the medium) should be removed, and the culture medium should not be completely sterilized.
7. Whether the air in the sterilized pan is clean.
This is affecting the relationship between sterilization temperature and pressure ratio is, the main points of the same at the same pressure, if the air is not clean, that is not pure steam sterilization, the temperature can not achieve the goal, will seriously affect the sterilization effect.
(source: food laboratory services)