Food Preservation 13.1

What is the impact of dry conditions on bacteria?

• They enhance bacterial growth

• They prevent enzymatic and metabolic processes

• They increase bacterial activity

• They promote bacterial reproduction

Answer explanation

Dry conditions limit water availability, which is crucial for enzymatic and metabolic processes in bacteria. This prevents their growth and activity, making the correct choice 'They prevent enzymatic and metabolic processes'.

What is the Aw value of flour stored at 20°C that prevents Clostridium perfringens growth?

• 0.1

• 0.4

• 0.7

• 1.0

Answer explanation

The Aw value of 0.4 is critical for preventing Clostridium perfringens growth in flour stored at 20°C. Values below this threshold inhibit bacterial growth, making 0.4 the correct choice.

What is the effect of high nutrient content in fresh meat?

• Reduces bacterial growth

• Enhances bacterial proliferation

• Neutralizes pathogens

• Inhibits spoilage

Answer explanation

High nutrient content in fresh meat provides an ideal environment for bacteria, leading to enhanced bacterial proliferation. This can increase the risk of spoilage and foodborne illnesses.

What is the effect of high-acid foods on spoilage organisms?

• Completely eliminates them

• Some may persist

• Enhances their growth

• Increases spoilage

Answer explanation

High-acid foods create an environment that inhibits many spoilage organisms, but some may still persist. This means that while the growth of certain bacteria is reduced, not all are eliminated.

What is the pH range where most pathogens cannot survive?

• Below 4.5

• 4.5–7.0

• 7.0–9.0

• Above 9.0

Answer explanation

Most pathogens cannot survive in highly acidic environments, specifically below a pH of 4.5. This low pH disrupts their cellular functions, making it inhospitable for their growth and survival.

What is the pH range of tomatoes?

• 3.0–3.5

• 4.0–4.4

• 5.0–5.5

• 6.0–6.5

Answer explanation

Tomatoes typically have a pH range of 4.0 to 4.4, making them slightly acidic. This range is important for their flavor and preservation, distinguishing them from more acidic fruits.

Listeria bacteria thrive on which of the following?

• Proteins and fats in raw milk

• Sugars in fruits

• Starch in bread

• Fiber in vegetables

Answer explanation

Listeria bacteria thrive on proteins and fats found in raw milk, making it a suitable environment for their growth. Other options like sugars, starch, and fiber are not ideal for Listeria.

What temperature should poultry be cooked to in order to prevent Campylobacter infection?

• 60°C

• 75°C

• 85°C

• 100°C

Answer explanation

Poultry should be cooked to an internal temperature of 75°C to effectively kill harmful bacteria like Campylobacter, ensuring food safety and preventing infection.

What is the impact of high water activity in milk?

• Reduces bacterial growth

• Enhances bacterial proliferation

• Neutralizes pathogens

• Inhibits spoilage

Answer explanation

High water activity in milk creates an environment conducive to bacterial growth, leading to enhanced bacterial proliferation. This can result in spoilage and potential health risks.

What happens to Bacillus cereus when cooked rice is left at room temperature for 4 hours?

• It becomes inactive

• It reaches dangerous levels

• It dies off

• It remains unchanged

Answer explanation

When cooked rice is left at room temperature for 4 hours, Bacillus cereus can multiply rapidly, reaching dangerous levels. This bacterium can produce toxins that cause foodborne illness, making this option the correct choice.