Figure 26.1 Decimal reduction 100 time(D) 50C 10 70C D is the time at which 60C only 10%of the original 1 population of organisms remain viable at a given temperature. 0.1 Effect of temperature on the viability of a mesophilic bacterium.The decimal reduction time,D,was obtained for the same mesophilic organism at three different temperatures.For 70C,D=3 min;for 60C,D=12 min;for 50C D=42 min
Figure 26.1 Decimal reduction time (D) Time (min) Survival fraction (log scale) 70C 60C 50C © 2012 Pearson Education, Inc. D is the time at which only 10% of the original population of organisms remain viable at a given temperature. Effect of temperature on the viability of a mesophilic bacterium. The decimal reduction time, D, was obtained for the same mesophilic organism at three different temperatures. For 70C, D = 3 min; for 60C, D = 12 min; for 50C, D = 42 min
100 (uIw) 100 a:mesophilic 10 10 B b:thermophilic 1 1 0.1 0.1 100105110115120125130 Temperature(C) 2012 Pearson Education,lnd. Relationship between temperature and D for two different microorganisms.For organism(a),a mesophile,exposure to for less than 20 s resulted in a decimal reduction,while for organism (b),a thermophile,10 min were required to achieve a decimal reduction
Relationship between temperature and D for two different microorganisms. For organism (a), a mesophile, exposure to for less than 20 s resulted in a decimal reduction, while for organism (b), a thermophile, 10 min were required to achieve a decimal reduction a: mesophilic b: thermophilic
上泽充通大￥ Shanghai Jiao Tong University Important term of heat sterilization ©Thermal death time(TDT)热致死时间 the time at which all cells are killed at a given temperature Measurement:heating samples of a cell suspension for different times,mixing the heated suspensions with culture medium,incubating and check growth o Shortcoming:such destruction is logarithmic,and it is theoretically not possible to "completely destroy" microorganisms in a sample..热致死是对数性的，理论上无 法“完全杀死”样品中所有微生物 Shanghai Jiao Tong University
Shanghai Jiao Tong University Thermal death time (TDT)热致死时间 • the time at which all cells are killed at a given temperature • Measurement: heating samples of a cell suspension for different times, mixing the heated suspensions with culture medium, incubating and check growth • Shortcoming: such destruction is logarithmic, and it is theoretically not possible to “completely destroy” microorganisms in a sample.热致死是对数性的,理论上无 法“完全杀死”样品中所有微生物 Important term of heat sterilization
上泽充通大学 Shanghai Jiao Tong University 6.1.2 Factors affecting efficiency of heat sterilization影响高温杀菌效果的因素 Presence of endospores determines the heating process.temperature and time内生芽孢决定了热 致死所需的温度和时间. Moist heat has better penetrating power than dry heat湿热比千热更具穿透力. Microbial cells die more quickly at acidic pH Dry cells and spores are more resistant to heat Higher concentrations of proteins,sugars and fats reduce heat penetration Shanghai Jiao Tong University
Shanghai Jiao Tong University 6.1.2 Factors affecting efficiency of heat sterilization 影响高温杀菌效果的因素 Presence of endospores determines the heating process- temperature and time内生芽孢决定了热 致死所需的温度和时间. Moist heat has better penetrating power than dry heat湿热比干热更具穿透力. Microbial cells die more quickly at acidic pH Dry cells and spores are more resistant to heat Higher concentrations of proteins, sugars and fats reduce heat penetration