The major physical agents or processes used for control of microorganisms are temperature , desiccation , osmotic pressure radiation and filtration
Microorganisms are omnipresent, occur everywhere on the surface of earth. Microorganisms are able to grow and survive under a wide range of environmental conditions. But there are limitations to the variations in the environment that particular species can tolerate . drastic change in the physical environment results in inhibition and or destruction of micro organisms.
- High temperature :
Micro organisms can grow over a wide range of temperature . each type has optimum, minimum and maximum growth temperature at which it will grow. Temperature above maximum exerts a killing effect, whereas temperature below minimum inhibits microbial growth..
Heat is the most widely used method of sterilisation and is one of the most effective, reliable and economic sterilizing agent. The amount of water present in the environment at any temperature has a significant effect upon micro organisms in terms of their survival.
High temperature along with high moisture is one of the most effective method of killing micro organisms.
Moist heat kills the micro organisms by coagulating their proteins and is more rapid and effective in killing the micro organisms as compared to dry heat which kills the micro organisms by oxidizing their chemical constituents
Vegetative cell of micro organisms are killed by exposure to temperature between 60-70 degree celsius for 5-10 minute. They are vert sensitive to heat as compared to spores. The higher amount of water in the vegetaative cell i responsible for it. Vegetative cells of yeast, fungi are killed in 5-10 minute by moist heat at 50-60 degree celsius.
How ever higher temperature are required to kill microbial spors. The spores of fungi and yeast are killed in 5-10 minute by moist heat at temperature 70-80 degree celsius. The spores of bacteria are the most heat resistant. Temperature above 100 C for extended time period is required to kill them. The susceptibility of most of viruses to heat is similar to that of vegetative cells. Certain terms are used as common basis for comparative studies in heat resistance of microorganisms