Food Preservation Quiz
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Questions and Answers

What is the primary objective of heat treatment in food preservation?

  • To increase the nutritional value of food
  • To change the texture of food
  • To enhance the flavor of food
  • To kill microbes that cause spoilage (correct)

Which factor influences the thermal resistance of microbial cells or spores?

  • The initial concentration of spores or cells (correct)
  • The color of the food
  • The type of packaging used
  • The flavor profile of the food

During which phase of growth do bacterial cells exhibit the greatest resistance to heat?

  • During the exponential phase
  • During the decline phase
  • During the early lag phase
  • During the maximum stationary phase (correct)

What is pasteurization primarily used for?

<p>To kill pathogens while preserving food quality (B)</p> Signup and view all the answers

What temperature range generally characterizes pasteurization?

<p>Below 100°C (A)</p> Signup and view all the answers

Which of the following methods can supplement pasteurization in food preservation?

<p>Refrigeration (D)</p> Signup and view all the answers

What happens to microbial proteins at high temperatures during heat treatment?

<p>They undergo coagulation or denaturation (B)</p> Signup and view all the answers

What occurs to the time required to kill cells or spores as the temperature increases?

<p>It decreases (C)</p> Signup and view all the answers

Which method is NOT effective in preventing microbial contamination during food preservation?

<p>Incorporation of additional moisture (D)</p> Signup and view all the answers

What is the primary goal of inhibiting microbial growth in food preservation?

<p>Extending shelf life (C)</p> Signup and view all the answers

Which process is used to inactivate food enzymes as a method of food preservation?

<p>Blanching (B)</p> Signup and view all the answers

Which method is most effective for preserving food by creating unfavorable conditions for microorganisms?

<p>High heat treatment (A)</p> Signup and view all the answers

What is the objective of extending the lag phase and phase of positive acceleration in food preservation?

<p>To reduce spoilage and increase storage life (B)</p> Signup and view all the answers

How does prevention of oxidation contribute to food preservation?

<p>By prolonging the shelf life of food (B)</p> Signup and view all the answers

Which of the following is NOT a chemical reaction that should be delayed in food preservation?

<p>Microbial metabolism (C)</p> Signup and view all the answers

What is a potential outcome of exposing microorganisms to sublethal heat treatments?

<p>They will require a richer culture medium for growth (C)</p> Signup and view all the answers

What is the primary purpose of ventilation in food storage rooms?

<p>To maintain uniform relative humidity (A)</p> Signup and view all the answers

What concentration of carbon dioxide is considered optimal for preserving eggs?

<p>2.5% (D)</p> Signup and view all the answers

Which gas combination is typically used for gas storage of food?

<p>Carbon dioxide and ozone (B)</p> Signup and view all the answers

What does the thermal death point (TDP) measure in microorganisms?

<p>The temperature necessary to kill microorganisms in a fixed time (B)</p> Signup and view all the answers

What is a major advantage of combining U.V. irradiation with chilling during food storage?

<p>It allows for higher storage temperatures (C)</p> Signup and view all the answers

What is the effect of freezing on microbial growth?

<p>Microbial growth is prevented entirely (D)</p> Signup and view all the answers

What is the D Value in thermal destruction of microorganisms?

<p>The time required to destroy 90% of microorganisms (C)</p> Signup and view all the answers

Which microorganism can grow at temperatures as low as 0-3°C?

<p>Yersinia enterocolitica (C)</p> Signup and view all the answers

Which method is used to inactivate plant enzymes before freezing vegetables?

<p>Scalding or blanching (B)</p> Signup and view all the answers

What is the typical temperature for common or cellar storage of food?

<p>Below 15°C (B)</p> Signup and view all the answers

What happens to chemical or enzymatic reactions at lower storage temperatures?

<p>They slow down (B)</p> Signup and view all the answers

Which food item is best stored at a temperature of 13.3 – 16.7°C?

<p>Bananas (C)</p> Signup and view all the answers

What is the main purpose of packing most foods before freezing?

<p>To prevent freezer burn and preserve quality (B)</p> Signup and view all the answers

How do low temperatures affect the enzyme activity in stored food?

<p>They slow down the enzymatic activity but do not prevent it (D)</p> Signup and view all the answers

What is a potential consequence of high humidity in food storage?

<p>Enhanced microbial spoilage of the stored food (B)</p> Signup and view all the answers

Which of the following best describes chilling storage temperatures?

<p>Not far above freezing, around -1 to 8°C (C)</p> Signup and view all the answers

What is the correct temperature and time combination for the HTST pasteurization method?

<p>71.7°C for 15 seconds (B)</p> Signup and view all the answers

Which method of pasteurization uses the lowest temperature for the longest duration?

<p>LTLT Method (D)</p> Signup and view all the answers

What does the phosphatase test indicate in milk pasteurization?

<p>Proper pasteurization of milk (D)</p> Signup and view all the answers

What temperature is required during boiling to adequately treat food?

<p>100°C (D)</p> Signup and view all the answers

Which process is referred to as Ultra Heat Temperature (UHT) processes?

<p>Sterilization using steam injection (B)</p> Signup and view all the answers

What is the characteristic temperature and duration that Clostridium botulinum spores can resist?

<p>120°C for 20 minutes (D)</p> Signup and view all the answers

What is the role of steam pressure during sterilization processes?

<p>It increases the temperature beyond 100°C. (C)</p> Signup and view all the answers

What happens during the alkaline phosphatase test if the milk has not been properly pasteurized?

<p>A color is produced. (B)</p> Signup and view all the answers

What is a characteristic of quick freezing compared to slow freezing?

<p>Formation of smaller ice crystals (B)</p> Signup and view all the answers

How long does it take to achieve slow freezing?

<p>Within 3–72 hours (B)</p> Signup and view all the answers

Which of the following statements is true regarding microorganisms during freezing?

<p>Cocci are generally more resistant than Gram-negative rods (A)</p> Signup and view all the answers

What is a primary advantage of quick freezing over slow freezing?

<p>Reduced microbial growth more promptly (C)</p> Signup and view all the answers

Which change occurs during the preparation for freezing that affects food deterioration?

<p>Conditions at harvesting can influence spoilage (D)</p> Signup and view all the answers

What happens to the metabolic rapport during quick freezing?

<p>It is broken down (C)</p> Signup and view all the answers

How does the freezing process affect lipids in foods?

<p>Unsaturated fatty acids are synthesized more at low temperatures (B)</p> Signup and view all the answers

What is the effect of thawing on quick frozen foods?

<p>It brings them to room temperature for cooking (B)</p> Signup and view all the answers

Flashcards

Lag phase

The stage in bacterial growth where there is no significant increase in the number of cells, but the bacteria are preparing for rapid growth.

Logarithmic (exponential) phase

The stage in bacterial growth where the number of bacteria increases rapidly.

Stationary phase

The stage in bacterial growth where the number of cells remains constant, as the rate of cell death equals the rate of cell division.

Death (decline) phase

The stage in bacterial growth where the number of cells decreases due to factors like nutrient depletion and accumulation of waste products.

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Filtration

A method of food preservation that involves removing microorganisms by physically filtering them out. This is often used for liquids like beer or wine.

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Low Temperature Preservation

A method of food preservation that involves lowering the temperature to inhibit microbial growth. This includes refrigeration and freezing.

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Heat Processing

A method of food preservation that involves using high temperatures to kill microorganisms. This can be achieved through methods like boiling, baking, or pasteurization.

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Drying

A method of food preservation that involves removing moisture from food, creating an environment where microorganisms cannot thrive. This includes methods like drying, dehydration, and salting.

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Heat Treatment in Food Preservation

The process of using high temperatures to kill microbes in food, making it safe to eat. This helps prevent spoilage and protects us from harmful bacteria.

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Objective of Heat Treatment

The key goal of heat treatment is to eliminate microorganisms that can cause food to spoil or make us sick.

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How Heat Kills Microbes

The method by which high temperatures damage or destroy microbes by altering their protein structure. This makes them unable to function and reproduce.

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Relationship Between Time and Temperature

The length of time required to kill microbes at a specific temperature.

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Initial Concentration of Spores

The more microbes present, the longer the heat treatment needs to be. This ensures that all harmful organisms are eliminated.

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Previous History of Microbes

The history of a microbe (where it grew and survived) influences its resistance to heat treatment.

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Phases of Growth and Heat Resistance

The phase of growth in a microbe's life cycle affects its heat resistance. Older and younger phases may have different resistance levels.

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Pasteurization

A heat treatment where temperatures are below 100°C, killing some but not all microbes. This is commonly used for milk and juice.

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HTST (High-Temperature Short Time)

A pasteurization method where food is heated to a high temperature (71.7°C) for a short time (15 seconds).

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LTLT (Low-Temperature Long Time)

A pasteurization method where food is heated to a lower temperature (62.8°C) for a longer time (30 minutes).

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Ultra Pasteurization

A pasteurization method using an even higher temperature (137.8°C) for a very short time (at least 2 seconds).

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Phosphatase Test

A test that checks if pasteurization was successful by detecting the presence of an enzyme (alkaline phosphatase) that is destroyed during proper pasteurization.

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Boiling

Food preservation method involving heating food at 100°C (boiling point of water), typically achieved by immersing the food in boiling water or steam.

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Sterilization

Food preservation method using temperatures exceeding 100°C, often achieved using steam under pressure in a retort or autoclave.

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UHT (Ultra High Temperature)

This heat treatment is sometimes referred to as 'Ultra Heat Treatment'. It typically involves heating milk to temperatures up to 150°C using steam injection, followed by rapid cooling.

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What is gas storage?

A controlled atmosphere where carbon dioxide, ozone, or other gases are introduced to extend shelf life.

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What is chilling or cold storage?

Using low temperatures to slow down microbial growth and enzymatic activity. This includes refrigeration and freezing.

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What are the benefits of gas storage for food?

Adding carbon dioxide or ozone can increase the shelf life of food and allows higher humidity without compromising quality.

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What is scalding or blanching?

The process of rapidly heating vegetables to inactivate enzymes, reduce microorganisms, and enhance color.

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How does scalding or blanching help preserve vegetables?

Enzymes, which are like tiny workers, are inactivated, preventing changes in texture, color, flavor, and nutritional value.

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What is freezing or frozen storage?

The process of preserving food by lowering its temperature to below freezing, preventing microbial growth and substantially slowing down enzymatic activity.

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How does freezing help preserve food?

Freezing slows down chemical and enzymatic reactions, ensuring food stays fresh for longer.

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What is the relationship between freezing temperature and food preservation?

The lower the temperature of frozen storage, the slower the chemical and enzymatic reactions occur, meaning the food stays fresh for a longer period.

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D-value

The time required to kill 90% of microorganisms at a specific temperature. Think of it as the time needed to reduce the population by a tenth.

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Thermal Death Point (TDP)

The minimum temperature needed to kill all microorganisms in a specific time (usually 10 minutes). It's like the 'death point' for microbes.

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Thermal Death Time (TDT)

This is the time needed to kill a specific number of microorganisms at a fixed temperature. Think of it as how long it takes to get rid of a specific number of microbes at a set temperature.

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Freezing vs. Refrigeration

Freezing involves temperatures below 0°C, effectively stopping the growth of most microorganisms. Refrigeration, on the other hand, involves temperatures above freezing, slowing down microbial growth.

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Yersinia enterocolitica Growth

Yersinia enterocolitica can thrive even at very low temperatures (0-3°C) which is why keeping food cold is important to prevent food poisoning.

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Common or Cellar Storage

Common storage keeps food between 15°C and 0°C, which can slow down spoilage but not prevent it entirely. It's good for short-term storage of foods like vegetables.

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Chilling Storage

Chilling storage is done close to freezing (between -1 to 8°C). It's suitable for many types of food but can cause some changes like 'sweating' due to temperature changes.

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Humidity in Low Temperature Storage

Humidity plays a crucial role in low temperature storage. Moisture on surfaces can encourage microbial growth leading to spoilage.

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Quick Freezing

Freezing process where temperatures reach -20°C within 30 minutes, resulting in small ice crystals that minimally damage cells.

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Slow Freezing

Freezing process that takes 3 to 72 hours, forming large ice crystals that damage cells and disrupt metabolism.

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Thawing

A process where frozen foods are brought to room temperature before consumption. This helps prevent texture changes and ensures proper cooking.

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Freezing on Microorganisms

Survival of microorganisms during freezing varies. Cocci are generally more resistant than Gram-negative rods. Endospores and toxins remain unaffected by low temperatures.

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Changes During Freezing

The condition of food before freezing significantly impacts deterioration. Temperature and other environmental conditions influence microbial growth and changes in the food.

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Freezing's Impact on Food Quality

The rate of freezing, formation of ice crystals, and disruption of metabolic processes all affect the quality of frozen food. Understanding these factors helps optimize freezing methods.

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Freezing and Enzyme Action

Freezing slows down enzymatic action. This helps preserve the food's quality and prevent undesirable changes.

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Advantages of Quick Freezing

Quick freezing is preferred over slow freezing because it minimizes damage to cells, slows microbial growth, and preserves food quality better.

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Study Notes

Food Preservation

  • Food preservation aims to prevent or delay microbial contamination and self-decomposition of food.

Principles of Food Preservation

  • Prevention or delay of microbial contamination:

    • Keeping out microorganisms (sterilization)
    • Removing microorganisms (e.g., filtration)
    • Inhibiting microbial growth (e.g., low temperature, drying, anaerobic conditions, chemicals)
    • Killing microorganisms (e.g., high heat, radiation)

  • Prevention or delay of self-decomposition of the food:

    • Destroying or inactivating food enzymes (e.g., blanching)
    • Preventing chemical reactions (e.g., oxidation using antioxidants)
    • Preventing damage caused by insects, animals, or mechanical causes

Application of Food Preservation

  • Lengthening the lag phase and the phase of positive acceleration is crucial.
    • Reduce the number of spoilage organisms by reducing contamination.
    • Avoid adding actively growing organisms to prevent contamination during growth phase of organisms.
    • Create unfavorable environmental conditions to slow or stop growth (e.g., temperature, pH, presence of inhibitors).
    • Damage organisms through processing methods like heating or irradiation.

Methods of Food Preservation: High Temperatures

  • The primary objective of heat treatment is to kill microbes causing food spoilage or posing health risks.
  • Heat denatures or clots microbial proteins, inactivating their vital functions, inhibiting metabolism enzymes, and damaging the cell wall.

Factors Influencing Thermal Resistance

  • Relationship between temperature and time: Higher temperatures result in shorter times for killing microorganisms.
  • Initial concentration: Higher initial numbers require longer or higher temperatures.
  • Previous history: Conditions in which cells live & how cells have grown affect the ability of spores or cells to resist heat.
  • Growth Phases: Microorganisms, in general, tend to exhibit greatest resistance during the late logarithmic to maximum stationary phases of growth.

Heat Treatments Employed in Processing Foods

  • Pasteurization (below 100°C): Kills part of the microorganisms but not all. Used to eliminate pathogens or when higher temperatures might harm quality.
    • Methods: steam, hot water, dry heat, electric currents; Cooling immediately after.
  • Boiling (around 100°C): Sufficient for killing many microbes but not spores. Suitable for low and medium acid foods.
  • Sterilization (above 100°C): Kills all microorganisms (including spores). Achieved via steam under pressure.
    • Ultra-Heat Treatment (UHT) involves steam injection or infusion with flash evaporation followed by rapid cooling to achieve high temperatures. Detection of effectiveness involves determining the presence of heat resistant organisms like Clostridium botulinum, resistant to high heat at 120°C for 20 minutes.

Thermal Destruction of Microorganisms

  • Thermal death time (TDT): Time needed to kill a given number of microbes at a fixed temperature.
  • Thermal death point (TDP): Temperature needed to kill a given number of microbes in a fixed time (e.g., 10 minutes).
  • D-value: Time required to decrease the number of live organisms by 90%.

Preservation by Use of Low Temperatures

  • Low temperatures slow down chemical reactions, enzyme action, and microbial growth.

Growth of Microorganisms at Low Temperatures

  • Freezing prevents the growth of most foodborne microorganisms.
  • Refrigeration slows growth rates.
  • Specific microorganisms have minimum growth temperatures (e.g. Clostridium botulinum type E 3.3°C; Yersinia enterocolitica 0-3°C)

Temperatures Employed in Low-Temperature Storage

  • Common/Cellar Storage: Typically below 15°C for root crops, potatoes and others.
  • Chilling/Cold Storage: Temperatures near freezing (-1 to 8°C).
    • Holds eggs, dairy, meats, seafood, vegetables and fruits for a limited time.
    • Using gas in addition to cold storage may extend storage time.
  • Freezing: Freezing prevents all microbial growth and significantly slows enzyme reactions. Methods vary regarding pre-processing and packaging.
  • Methods like scalding/blanching are used for vegetables prior to freezing.

Quick Freezing vs. Slow Freezing

  • Quick freezing: Forms smaller ice crystals, preserving cell structure.

  • Slow freezing: Forms larger crystals. Damages cell structure to a greater degree.

Effect of Freezing on Microorganisms

  • Cocci (spherical) bacteria are more resistant to freezing than rods.
  • Endospores and toxins are unaffected.
  • Low temps impact fatty acids, causing some changes to lipids' unsaturated fatty acids.

Changes during preparation for Freezing

  • Conditions at harvesting, slaughter, and handling influence food's deterioration rate. Temperatures and handling will result in different microbial growth and changes.

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Food Preservation Lecture Notes PDF

Description

Test your knowledge on the principles of heat treatment and food preservation methods. This quiz covers key concepts such as pasteurization, thermal resistance of microorganisms, and the goals of inhibiting microbial growth. Discover how various techniques contribute to extending the shelf life of food.

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