Microbiological testing is based on culture media, which has a direct impact on the results. This is because microbe development need not only a plentiful supply of nutrients, but also a pH environment that is conducive to their growth. Microorganisms can only grow and reproduce correctly or reflect their biological traits in a pH environment that is appropriate for them. The sterilizing procedure has a significant influence on the pH values of culture medium during the preparation phase. We frequently see a pH difference in culture medium before and after sterilisation, with the pH value typically dropping after sterilisation. We shall discuss the variations in pH before and after sterilisation in this post.
High temperatures during autoclaving can have a number of detrimental consequences on culture medium, including nutrient breakdown, nutrient content changes, and pH changes, all of which can impact microbial growth. The temperature and time of sterilisation, the rate of temperature rise and fall in the autoclave, the volume of the sterilisation vessel, and the loading technique all have an impact on the sterilisation of culture medium during the sterilisation process.
Varying culture media with the same sterilisation temperature and duration, as well as the same volume and loading capacity, exhibit different pH changes following sterilisation, with some culture mediapH values changing more and some culture mediapH values changing less. After sterilisation, the pH of the culture medium varied, with some altering more and others changing less. This is due to the fact that various culture media have distinct compositions, and different components have varying impacts on the ph values of culture media during sterilisation. Sugars and peptones are two of the most prevalent and significant components of culture medium; how do they impact the pH following sterilisation?
Microorganisms use sugars as a carbon source, such as glucose and lactose. Sugars create organic acids at high temperatures, lowering the pH of the culture medium. The lower the pH value following sterilisation, the higher the sugar content of the culture medium. If you over-sterilize anything, the pH shift is more noticeable. Simultaneously, when sugars are sterilised at high temperatures, they caramelize, darkening the color of culture medium.
Peptone is commonly used as a nitrogen source in culture medium to provide nutrients for microorganism development. Peptones also act as a buffer, preventing the pH of culture medium from changing during sterilisation. Culture medium with a high peptone concentration have a slight pH shift before and after sterilisation in general. Furthermore, if culture medium contains buffering agents, such as dipotassium hydrogen phosphate, the pH shift before and after sterilisation of culture media can be reduced.
The pH of the same culture material measured at various temperatures might change to some degree. This is because the amount of free ions in the solution grows at higher temperatures, resulting in lower pH values, while the number of free ions in the solution reduces at lower temperatures, resulting in higher pH values. When testing culture mediapH values, we usually keep the temperature around 25°C.