BIOL240 Lecture Notes - Microorganism, Disinfectant, Boiling Point
Document Summary
Learning objectives: to consider methods for controlling microorganisms and appreciate the challenges associated with these methodologies. Until now, we have been considering growth characteristics of microorganisms. Now, we"ll look at how to inhibit their growth or kill them. A given organism will have a characteristic sensitivity to temperature, with death occurring more rapidly at higher temperatures. There is an exponential relationship between time of heating and extent of killing. Endospores are much more resistant to heat than are vegetative cells. For this reason, heat sterilization is aimed at ensuring that endospores are killed. At the autoclave temperature of 121 c, endospores have a decimal reduction time of 4- 5 minutes. Moist heat is more effective than dry heat, since it can penetrate the object being sterilized more effectively. The high temperature within the autoclave, above the boiling point of water, is achieved under pressure (figure 26. 3). A very common method of reducing the numbers of microorganisms in foods is pasteurization.