1/17/2016 As early as the stone age,humans have been When selecting the method of microbial control, using some type of physical method of microbial control to preserve food. you must consider what else besides the microbe will the method affect. Drying and Salting were probably the most common early techniques. Heat will inactivate vitamins or antibiotics in a solution Repeated heating damages laboratory and hospital equipment. Economic considerations:using presterilized,disposable plasticware versus washing and resterilization of glassware. Heat:Mode of Action and Relative Thermal Death Measurements Effectiveness Heat resistance varies among different microbes and Moist heat is expressed as TDP. .lower temperatures and shorter Thermal Death Point (TDP)-the lowest temperature at which all microbes in a particular exposure time liquid will be killed in 10 minutes coaqulation and denaturation of proteins Length of time to sterilize is expressed as TDT. Thermal Death Time (TDT)-minimal length of Dry heat time for all bacterial in a particular liguid to be killed at a given temperature .moderate to high temperatures .dehydration Third concept related to heat resistance: Decimal reduction time(DRT)-the time,in .alters protein structure minutes,in which 90%of the population of .incineration bacteria at a given temperature will be killed 1/17/2016 5 As early as the stone age, humans have been using some type of physical method of microbial control to preserve food. Drying and Salting were probably the most common early techniques. When selecting the method of microbial control, you must consider what else besides the microbe will the method affect. • Heat will inactivate vitamins or antibiotics in a solution • Repeated heating damages laboratory and hospital equipment. • Economic considerations: using presterilized, disposable plasticware versus washing and resterilization of glassware. Heat: Mode of Action and Relative Effectiveness Moist heat •lower temperatures and shorter exposure time • coagulation and denaturation of proteins Dry heat • moderate to high temperatures • dehydration • alters protein structure •incineration Thermal Death Measurements Heat resistance varies among different microbes and is expressed as TDP. Thermal Death Point (TDP) – the lowest temperature at which all microbes in a particular liquid will be killed in 10 minutes Length of time to sterilize is expressed as TDT. Thermal Death Time (TDT) – minimal length of time for all bacterial in a particular liquid to be killed at a given temperature Third concept related to heat resistance: Decimal reduction time (DRT) – the time, in minutes, in which 90% of the population of bacteria at a given temperature will be killed