Food Preservation and Drying Methods
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Questions and Answers

What is the typical drying time for vegetables?

  • 24-36 hours
  • 48 hours
  • 6-16 hours (correct)
  • 1-5 hours

A high moisture content food like lettuce is suitable for drying.

False (B)

What do lower atmospheric pressures do to the dehydration process?

They accelerate evaporation at lower temperatures.

Dehydration reduces water activity (Aw) below _____ to stop spoilage.

<p>0.5</p> Signup and view all the answers

Match the factors affecting the drying rate with their descriptions:

<p>Speed of Airflow = Affects product quality and drying speed Size of Food Particles = Smaller pieces dry faster than larger ones Surface Area = Larger areas facilitate faster drying Temperature = Low temperature encourages microbial growth</p> Signup and view all the answers

What is one objective of the drying process?

<p>To delay ripening (A)</p> Signup and view all the answers

Increasing the surface area of food reduces drying efficiency.

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

What may pre-treatment during the drying process help prevent?

<p>Discoloration</p> Signup and view all the answers

What is the ideal drying temperature for the dehydration process?

<p>65–70°C (D)</p> Signup and view all the answers

Dehydration increases the moisture content of food.

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

What is the primary purpose of dehydration in food preservation?

<p>To extend shelf life by reducing water activity.</p> Signup and view all the answers

Foods should have a moisture content below __________ for safe storage.

<p>20%</p> Signup and view all the answers

Match the food items to their respective categories:

<p>Raisins = Commercial dried foods Egg powder = Dried ingredients Coffee = Commercial dried foods Powdered milk = Transformed foods</p> Signup and view all the answers

What is a common method to prevent browning during the dehydration process?

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

Browning in dehydrated foods can be caused by high temperature or oxidation.

<p>True (A)</p> Signup and view all the answers

Name one factor that affects the drying process of foods.

<p>Drying temperature, relative humidity, or velocity of air.</p> Signup and view all the answers

What is the primary disadvantage of using cobalt-60 (Co60) in food irradiation?

<p>Requires frequent replenishment (C)</p> Signup and view all the answers

Food becomes radioactive after being irradiated.

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

List one characteristic of accelerated electrons (E-Beams) used in food irradiation.

<p>Maximum energy of 10 MeV.</p> Signup and view all the answers

Food irradiation is also referred to as _____ pasteurization.

<p>cold</p> Signup and view all the answers

Which of the following is NOT an advantage of food irradiation?

<p>Always improves the taste of food (B)</p> Signup and view all the answers

Match the following food items with their usage in irradiation:

<p>Potatoes = Fresh produce Onions = Fresh produce Cereals = Grains Poultry = Meat</p> Signup and view all the answers

What is one major advantage of using E-Beams over Co60 for food irradiation?

<p>Can be turned off as needed (B)</p> Signup and view all the answers

What is the purpose of exposing food to controlled amounts of ionizing radiation?

<p>To reduce or eliminate disease-causing microorganisms.</p> Signup and view all the answers

Flashcards

Dehydration

The process of removing water from food using heat under controlled conditions, resulting in evaporation.

Dehydrated Food

Foods with less than 2.5% water content (on a dry basis) are considered dehydrated.

Purpose of Dehydration

The removal of water from food extends its shelf life by reducing water activity, making it less hospitable to microbes.

Dehydration Process

Dehydration involves applying heat and simultaneously removing moisture, leading to a change in the food's physical and chemical properties.

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Drying Temperature

The ideal drying temperature is between 65-70°C (149-158°F). High heat can burn the food.

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Relative Humidity's Role in Drying

Lower humidity and higher temperature accelerate drying.

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Air Velocity in Drying

Faster airflow during dehydration removes moisture from the food's surface.

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Blanching

The process of heating food briefly before dehydration to preserve color and flavor.

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Moisture Content

The amount of water in a food, measured as a percentage.

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Drying Rate

The rate at which water evaporates from food during drying.

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Moisture Absorption

The ability of food to absorb moisture from the air surrounding it.

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Water Activity (Aw)

The measure of available water for microorganisms to grow in food.

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Case Hardening

When rapid drying creates a hardened outer layer while the inside remains moist, leading to uneven drying.

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Drying Chamber

The space within a drying equipment where food is placed for dehydration.

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Tray Loading

The number of trays placed in a dryer, which affects drying performance.

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Food Irradiation

Ionizing radiation, like gamma rays or electron beams, is used to sterilize food and extend its shelf life.

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Mechanism of Food Irradiation

Food irradiation targets and disrupts the DNA of bacteria and other microbes, eliminating their ability to multiply and cause spoilage.

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Irradiation Process

The process involves exposing food to a controlled dose of ionizing radiation, which can be from gamma rays or electron beams. The duration of exposure depends on the food type and desired outcome.

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Cobalt-60 (Co60)

Cobalt-60 is a radioactive isotope used as a gamma ray source in food irradiation. Its half-life is 5.27 years.

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Electron Beams (E-Beams)

Electron beams are produced by powerful electron guns that generate high-energy electrons.

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Advantages of E-Beams

E-Beams can be turned on and off as needed, allowing for more precise control over the irradiation process. They also don't require frequent replenishment.

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Food Safety of Irradiation

Food irradiation doesn't make the food radioactive. The process only disrupts harmful bacteria and insects.

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Nutritional Impact of Irradiation

Food irradiation doesn't significantly alter the nutritional value of food, preserving its vitamins, minerals, and other essential nutrients.

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Study Notes

Food Preservation

  • Food preservation extends the shelf life of food products by reducing water activity, inhibiting microbial growth, or slowing down chemical reactions that cause spoilage.
  • Dehydration is a method of food preservation that involves removing water from food products, thus decreasing water activity and inhibiting microbial growth and enzyme activity.
  • Factors affecting drying rate include temperature, airflow/velocity, relative humidity, moisture content of food, surface area of food, food particle size and atmospheric pressure.

Drying Methods

  • Conventional Drying: Uses heat through heated air or direct contact.
  • Vacuum Drying: Removes water under vacuum, e.g., freeze drying where solid ice turns to vapor.
  • Osmotic Drying: Utilizes osmosis to draw water out of the food.
  • Sun/Solar Drying: Food is exposed to direct sunlight, utilizing a renewable energy source.
  • Microwave Drying: Uses high-frequency electromagnetic waves.
  • Freeze Drying: Food is frozen and then placed in a vacuum chamber to sublimate ice directly into vapor.
  • Drum Drying: Suitable for high viscosity liquids or slurries, involves spreading food over a rotating heated drum.
  • Spray Drying: Converts liquid into a fine mist sprayed into a hot air chamber.
  • Tunnel Drying: Combines heated air and moving trays throughout a tunnel.
  • Roller Dryer: Food is spread on a heated rotating drum.
  • Vacuum Shelf Dryer: Operates under vacuum conditions.

Objectives of Drying

  • Reduce water content to below 25% or an aw (water activity) of 0.00–0.60;
  • Extend shelf life;
  • Reduce enzyme activity;
  • Reduce microbial growth and inhibit undesirable chemical reactions;
  • Reduce packaging, storage, and transport costs;
  • Produce ready to eat foods that don't need refrigeration.

Factors Affecting Drying

  • Drying/Airflow Speed: Affects quality, must be controlled to avoid case hardening.
  • Temperature: High heat can scorch; low temperature increases drying time.
  • Humidity: Low humidity increases rate of drying.
  • Air Velocity: Faster air flow increases drying rate.
  • Food Size/Surface Area: Smaller pieces or larger surface areas dry faster.
  • Moisture Content of Food: Foods with high moisture are unsuitable for drying.
  • Capacity of Dryer: Affects drying performance and time needed.
  • Tray Loading: Affects drying performance.
  • Product Type: Vegetables, fruits, and grains have different drying times and requirements.

Hurdle Technology

  • Food preservation using a combination of multiple preservation techniques;
  • Hurdles disrupt microbial homeostasis (e.g., by disrupting cell membranes or DNA);
  • A combination of multiple hurdles at low concentrations is more effective than a high concentration of one hurdle.
  • Factors considered for selection are initial microbial load, conditions favorable for growth, desired shelf life, expected reactions and quality, quantity of expected microorganisms.
  • Examples include combinations of heat, salt, pH, and reduced water activity.

Irradiation

  • Food irradiation exposes food to carefully controlled doses of ionizing radiation, achieving preservation objectives.
  • Mechanisms include damaging DNA, affecting cell membranes, and breaking chemical bonds.
  • Types include gamma rays, electron beams, and X-rays.
  • Applications include sterilization, pathogen control, insect disinfestation, and delaying ripening.

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Related Documents

Food Preservation Techniques - Dehydration PDF

Description

This quiz covers food preservation techniques and various drying methods used to extend the shelf life of food. It discusses factors affecting drying rates and different approaches such as conventional, vacuum, osmotic, solar, and microwave drying. Test your knowledge on how these methods inhibit spoilage and promote food safety.

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