Actions of Microbial Control Agents Alternation of membrane permeability 。Damage to proteins Damage to nucleic acids
• Alternation of membrane permeability • Damage to proteins • Damage to nucleic acids Actions of Microbial Control Agents
Physical Methods of Microbial Control 。Heat Thermal death point (TDP):Lowest temperature at which all cells in a culture are killed in 10 min. Thermal death time (TDT):Time to kill all cells in a culture Decimal reduction time(DRT):Minutes to kill 90%of a population at a given temperature
• Heat • Thermal death point (TDP): Lowest temperature at which all cells in a culture are killed in 10 min. • Thermal death time (TDT): Time to kill all cells in a culture • Decimal reduction time (DRT): Minutes to kill 90% of a population at a given temperature Physical Methods of Microbial Control
Heat Moist heat Exhaust valve (to remove Steam to Safety Pressure Operating valve(controls steam steam after sterilization) chamber valve gauge from jacket to chamber) denatures proteins Autoclave: Steam Steam under chambe pressure Perforated shelf Sediment screen Steam jacket Thermometer Automatic ejector valve is Pressure regulator thermostatically controlled for steam supply and closes on contact with pure steam when air is To waste line exhausted. Steam supply Figure 7.2
• Moist heat denatures proteins • Autoclave: Steam under pressure Heat Figure 7.2
Physical Methods of Microbial Control Pasteurization reduces spoilage organisms and pathogens Equivalent treatments 。63°Cfor30min 。High-temperature short-time72°Cfor15sec 。Ultra-high-temperature::140°Cfor<1sec Thermoduric organisms survive
• Pasteurization reduces spoilage organisms and pathogens • Equivalent treatments • 63°C for 30 min • High-temperature short-time 72°C for 15 sec • Ultra-high-temperature: 140°C for <1 sec • Thermoduric organisms survive Physical Methods of Microbial Control
Physical Methods of Microbial Control Dry Heat Sterilization kills by oxidation 。Flaming 。Incineration Hot-air sterilization Hot-air Autoclave Equivalent treatments 170°C,2hr 121°C,15min
• Dry Heat Sterilization kills by oxidation • Flaming • Incineration • Hot-air sterilization Physical Methods of Microbial Control Hot-air Autoclave Equivalent treatments 170˚C, 2 hr 121˚C, 15 min