Affect the quality of medium sterilization
1. Maintenance of nutrients
In humid heat sterilization, microorganisms are killed simultaneously.mediumNutrient components are also damaged to a certain extent, especially amino acids and vitamins. For example, at 121 ° C, only 20 minutes, 59% of lysine, arginine and other basic amino acids are destroyed, and methionine and tryptophan are also destroyed in considerable quantities. Under the action of heat, some nutrients may also react with each other due to heat, causing changes in the quantity of original nutrients in the medium, thus affecting the quality of the medium.
2. Heat tolerance of microorganisms
The thermal resistance of bacterial spores is large, and the time required for sterilization depends on the time required to reduce bacterial spores to a specified number.
3. pH value
It has a significant impact on the heat tolerance of microorganisms.pHWhen the value is between 6.0 and 8.0, microorganisms are least likely to die. At pH < 6.0, microorganisms are more likely to die. At this time, H + can easily penetrate into the cells of microorganisms, thereby changing the physiological response of cells and promoting their death. Therefore, the lower the pH of the medium, the shorter the time required.
4. Media composition
High concentrations of organic matter composed of oils, sugars, and proteins will coat the cells in the form of a film, affecting heat conduction. High concentrations of salts and pigments weaken their heat resistance and make it easier to sterilize. For example, E. coli will die when heated to 60-65 ° C in water, 70 ° C in 10% sugar solution for 4-6 minutes, and 30% sugar solution for 30 minutes.
5. Foam
The air in the foam forms an insulating layer that makes it difficult for heat to penetrate and kill bacteria.
6. Pellets
Small particles, easy to sterilize, large particles, difficult to sterilize. For medium containing a small amount of larger particles and crude fibers, it can be removed by coarse filtration (should not affect the quality of the medium). Medium agglomeration will cause incomplete sterilization of the medium.
