micro 13.2 pt 3

Thermal death point (TDP)

The lowest temperature at which all microorganisms are killed in a 10-minute exposure.

Thermal death time (TDT)

The length of time needed to kill all microorganisms in a sample at a specific temperature.

Heat-resistant microorganisms

Endospore-forming microorganisms, such as Clostridium botulinum.

Boiling and sterilization

Boiling is not considered a sterilization method because some endospores can survive boiling, even for many hours.

Effect of altitude on boiling

Boiling is less effective at high altitudes because water boils at a lower temperature.

Advantage of moist heat over dry heat

Moist heat penetrates cells more effectively.

Common autoclaving temperature

121°C or 132°C, depending on the cycle.

Typical autoclave pressure

Approximately 15–20 psi.

Importance of steam contact in sterilization

Direct contact allows the steam to transfer enough heat to destroy microorganisms and endospores.

Purpose of autoclave tape

It indicates that the autoclave reached the appropriate temperature due to color change in its stripes.

Limitations of autoclave tape

It does not prove sterility, as it doesn't indicate proper temperature exposure duration.

Biological indicator spore test

A test using highly heat-resistant endospores to verify that an autoclave has successfully killed them.

Gold standard organism for autoclave testing

Geobacillus stearothermophilus.

HTST pasteurization

Heating milk to 72°C for 15 seconds.

UHT pasteurization

Heating milk to approximately 138°C for 2 or more seconds.

Advantage of UHT pasteurization

Properly sealed UHT milk can be stored for long periods without refrigeration.

Household refrigerator temperature range

Approximately 0°C–7°C.

Refrigeration and microorganism control

It slows microbial metabolism and growth.

Refrigeration effect on bacteria

Refrigeration does not kill bacteria; it primarily slows their growth.

Bacterial growth upon thawing frozen food

Microbial growth can resume, so thawed food should be treated like fresh perishable food.

Long-term preservation temperatures for bacteria

−70°C or lower.

High-pressure processing (pascalization)

Using very high pressure to kill microorganisms in food while preserving food quality.

High-pressure processing pressure range

Approximately 100–800 MPa.

High pressure's effect on microbial cells

It causes protein denaturation and damages cellular structures.

Endospores and high-pressure processing

Endospores can survive high-pressure processing.

Desiccation

Drying or dehydration that removes water needed for microbial metabolism and survival.

Survival of microorganisms in desiccation

Not all microorganisms die; some can survive and resume growth when water becomes available.

Lyophilization

Freeze-drying: rapidly freezing material and placing it under a vacuum to remove water by sublimation.

Sonication

Using high-frequency ultrasound waves to create cavitation that disrupts and can lyse cells.

Effect of salt or sugar on food preservation

It creates a high-osmotic-pressure environment that draws water out of microbial cells, reducing available water and inhibiting growth.