FSC-342 Quiz #2 : Lecture 5 - Extrinsic Factors that Impact Microbial Growth

What effect does refrigeration have on microbial growth?

Microbial cells grow slower compared to room temperature.

How can prior heat exposure affect Listeria monocytogenes?

Preheating at 48°C for 2 hours increases its thermotolerance.

What are psychrophiles?

Cold-loving bacteria that grow optimally at 15°C and cannot grow above 25°C.

What are psychrotrophs?

Cold-tolerant bacteria (e.g., Listeria monocytogenes, Clostridium botulinum) that grow optimally at 25°C and cannot grow above 40°C.

What are mesophiles?

Bacteria that grow between 20°C to 45°C, like Salmonella and pathogenic E. coli.

What are thermophiles?

Bacteria that grow between 41°C and 70°C.

Define hazard in food safety.

the potential to cause harm or be a source of damage.

Define risk in food safety.

the probability that a hazard will lead to injury.

What is hurdle technology?

A method that deoptimizes multiple factors to inhibit microbial growth rather than pushing one factor to an extreme.

What is an example of using hurdle technology?

Using pH 5.2 and aW 0.92 to prevent pathogen growth instead of pushing pH to 4.6 or aW below 0.85.

How are federal canning rules related to hurdle technology?

They integrate pH and water activity (aW) to determine the necessary processing, like boiling water or pressure retort.

Why are multiple hurdles effective in food preservation?

Because they force bacteria to use energy for survival instead of growth, leading to inhibition or death.

What are the stages of the spore life cycle?

Sporulation → Dormancy → Activation → Germination → Outgrowth.

Why are spores important in food safety?

They can survive heat, drying, and chemicals and can cause illness and spoilage in low-acid and refrigerated foods.

What pathogens are major spore-formers relevant to public health?

Clostridium botulinum, Clostridium perfringens, and Bacillus cereus.

What are the two types of Clostridium botulinum?

Proteolytic & Non-proteolytic; both produce heat-resistant spores.

How does Clostridium perfringens vary in heat resistance?

D90°C values from 15 to 145 minutes, spores 3 to 5 minutes.

What are the toxins produced by Bacillus cereus?

A heat-labile enterotoxin (diarrhea) and a heat-stable emetic toxin (vomiting).

How many cells of B. cereus typically cause illness?

Generally requires >10^6 cells per gram of food.

What is the structure of a bacterial spore?

Seven layers: exosporium → coats → outer membrane → cortex → germ cell wall → inner membrane → core.

Why is the spore core so resistant?

Low water content, high Ca-DPA, SASP-bound DNA, and a tight inner membrane protect from damage.

What triggers spore germination?

Nutrients (amino acids, sugars) or non-nutrient triggers (salts, DPA)

What is a D-value?

Time at a set temperature to reduce microbial population by 1 log (90%).

What is a Z-value?

Temperature increase needed to reduce the D-value by 10 times.

What is the target pathogen for low-acid canned food?

Proteolytic Clostridium botulinum.

What temperature/time inactivates C. botulinum in food processing?

121°C for ≥2.4 minutes.

Why is rapid chilling important after cooking?

To prevent C. perfringens spore germination and growth.

What organism causes off-flavors in acid juices after pasteurization?

Alicyclobacillus.

True or False: Pasteurized crabmeat (85°C, 10 min) does not require refrigeration to control Group II C. botulinum.

False. Refrigeration is still necessary.