Thorough sterilization of the culture culture media directly affects the scientific research testing data. Many factors affect the sterilization of the culture culture media, apart from the types and quantity of impurities in the culture media, sterilization time and temperature, it also depends on the following:
During wet-heat sterilization, while microorganisms are killed, the nutritional components of the culture media are also damaged to a certain extent, especially amino acids and vitamins. For example, at 121℃ for only 20 minutes, 59% of lysine and arginine, and other basic amino acids are destroyed. Cysteine and tryptophan are also significantly damaged. Under the heat, certain nutritional components may also react with each other, resulting in changes in the quantity of the original nutrient components in the culture culture media, thereby affecting the quality of the culture media.
The heat resistance of bacterial spores is greater, and the time needed for sterilization depends on the time it takes to reduce bacterial spores to the specified number.
The pH value has a great influence on the heat resistance of microorganisms. When the pH value is between 6.0-8.0, microorganisms are the least likely to die. When the pH value is less than 6.0, microorganisms are more prone to death. At this time, pH can easily penetrate into the cells of microorganisms and change their physiological reactions, causing them to die. Therefore, the lower the pH of the media in microbiology, such as agar based medium, the shorter the required time.
High concentrations of organic compounds such as fats, sugars, and proteins are wrapped around cells in the form of a thin film, affecting heat transfer. High concentrations of salts and pigments weaken heat resistance, making sterilization easier. Different media in microbiology have different features. For example: Escherichia coli dies when heated in water to 60-65℃, it needs to be heated at 70℃ for 4-6 minutes in 10% sugar solution before it dies, 30 minutes in 30% sugar solution. For general culture media, it is best to choose 121℃ for 20 minutes.
The air in the foam forms a heat-insulating layer, making it difficult for heat to penetrate and kill impurities, thus affecting the sterilization effect of the culture media.
Small particles are easy to sterilize, while large particles are difficult to sterilize. For culture media containing a small amount of larger particles and coarse fibers, they can be removed by coarse filtration method (which should not affect the quality of the culture media), and clumping of the culture media can cause incomplete sterilization.
This is a key point affecting the temperature and pressure ratio of the sterilization of the culture media. Under the same pressure, if the air is not exhausted, that is, it is not pure steam sterilization, the temperature may not necessarily meet the required standard, which will seriously affect the sterilization effect of the culture media.