Food Preservation Techniques: Dehydration

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Questions and Answers

What is one purpose of dehydration in food preservation?

  • Increases the need for preservatives
  • Prevents all nutrient loss
  • Extends shelf life by reducing water activity (correct)
  • Enhances flavor substantially

What does food irradiation primarily reduce or eliminate?

  • Flavor compounds
  • Nutritional value
  • Chemical additives
  • Disease-causing microorganisms (correct)

Color changes like browning during drying can be prevented with proper treatment.

True (A)

What is the ideal drying temperature for food?

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

Food treated with irradiation becomes radioactive.

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

Which food items typically require a drying time of 6–16 hours?

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

The process of removing water from food through heat application is called __________.

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

What is the maximum energy level achieved by accelerated electrons in food irradiation?

<p>10 MeV</p> Signup and view all the answers

High moisture foods such as lettuce are suitable for drying.

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

Match the following dried foods with their categories:

<p>Coffee = Commercial dried food Egg powder = Dried ingredient Raisins = Commercial dried food Yeasts = Dried ingredient</p> Signup and view all the answers

Irradiation can be described as '________ pasteurization' as it achieves similar safety objectives without high temperature.

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

What effect does drying have on microbial spoilage?

<p>It reduces microbial spoilage.</p> Signup and view all the answers

Which of the following factors does NOT affect the drying process?

<p>Type of food packaging (A)</p> Signup and view all the answers

The primary objective of drying is to reduce _____ content in food.

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

Which of the following is NOT a characteristic of the electron beam irradiation method?

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

Match the following food items with their type of radiation treatment:

<p>Potatoes = Ionizing radiation Onions = E-Beams Cereals = Cold pasteurization Poultry = Thermal pasteurization</p> Signup and view all the answers

Match the food types with their typical drying times:

<p>Vegetables = 6-16 hours Fruits = up to 48 hours Grains = 10-15% moisture content Lettuce = unsuitable for drying</p> Signup and view all the answers

Dehydrated food contains more than 2.5% water.

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

What is a disadvantage of using Co60 pencils in food irradiation?

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

What happens to the drying rate if the size of food particles is smaller?

<p>Drying time decreases (B)</p> Signup and view all the answers

What is the oldest method of preserving food through dehydration?

<p>Solar/sun drying</p> Signup and view all the answers

Lower atmospheric pressure during drying allows for evaporation at higher temperatures.

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

Irradiation serves as an effective technology for preventing foodborne diseases.

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

What is the impact of temperature on the drying process?

<p>Low temperatures encourage microbial growth.</p> Signup and view all the answers

Flashcards

Dehydration

The process of removing moisture from food, which inhibits microbial growth and spoilage.

Water Activity (Aw)

The amount of water available for microbial growth and activity. It is reduced during dehydration.

Drying Rate

The rate at which water evaporates from the food during dehydration.

Airflow and Temperature

The temperature and airflow used during dehydration. High airflow speeds up drying but can impact product quality.

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Pre-treatment

Pre-treating food (e.g., blanching) before dehydration to prevent discoloration or unwanted changes.

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Uniform Drying

The process of creating a uniform moisture content throughout the food during dehydration to prevent uneven drying.

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Case Hardening

A condition where the outer surface of a food dries too quickly, creating a hard outer layer while the inside remains moist.

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Moisture Absorption

The ability of the surrounding air to absorb moisture. Higher humidity slows down the drying process.

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Drying

The process of removing moisture from food using a combination of heat application and moisture removal.

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Moisture content

The amount of water present in a food, expressed as a percentage of the total weight.

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Blanching

A pre-treatment step in food preservation that helps preserve color and flavor during dehydration.

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Shrinkage

The change in the size and shape of food due to water loss during dehydration.

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Browning

The browning of food during dehydration caused by high temperatures or oxidation.

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Loss of flavor

The loss of volatile compounds that contribute to the flavor of food during dehydration.

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Loss of nutritional value

The loss of water-soluble nutrients, such as Vitamin C, due to dehydration.

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Food Irradiation

A process that uses controlled amounts of ionizing radiation to extend shelf life and reduce harmful microorganisms in food.

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Irradiation

A technique involving exposing food to a controlled dose of ionizing radiation, usually gamma rays or electron beams, to eliminate harmful microorganisms and extend shelf life.

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Gamma Irradiation

Gamma rays emitted by radioactive cobalt-60 are used to irradiate food, penetrating deep into the product to kill harmful microorganisms.

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Accelerated Electron (E-Beam) Irradiation

A type of irradiation that involves bombarding food with high-energy electrons produced by electron guns. It is effective for treating thinner products like poultry and fresh produce.

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Electron Beam Irradiation

A type of irradiation that involves directing high-energy electrons at food, penetrating to a depth of 3 cm. It is useful for reducing bacteria on the food surface.

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Food Irradiation and Radioactivity

Food exposed to irradiation does not become radioactive. The process only modifies the structure of harmful microorganisms, rendering them harmless.

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Food Irradiation Benefits: Disease Reduction

Irradiation effectively reduces or eliminates disease-causing microorganisms in food, reducing the risk of foodborne illnesses.

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Food Irradiation Benefits: Nutritional Value

Food treated with irradiation retains its nutritional value, ensuring that consumers receive essential vitamins and minerals from the food.

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Study Notes

Food Preservation Techniques

  • Dehydration: Removing water from food to extend shelf life. Foods dehydrated to less than 2.5% water are considered dried.

  • Dehydration Theory: Heat application combines with moisture removal to extend shelf life. Examples include dried foods like coffee, milk, raisins, pasta, beans, and spices.

  • Dehydration Process: Oldest method is solar drying, followed by pre-treatments to preserve color and flavor, and drying the food whole or transforming it into powder (e.g., powdered milk, dried fish).

  • Dehydration Principles: All organisms need water, dehydration stops spoilage by decreasing water activity and enzyme activity, and reduces microbial spoilage, concentrating sugars in fruits.

  • Factors Affecting Drying: Drying temperature (65-70°C initially, dropping to 60°C), moisture content (less than 20% for fruits, 10% for vegetables, 10-15% for grains), relative humidity, airflow velocity, drying time, tray loading, food particle size, and atmospheric pressure and vacuum.

  • Advantages of Dehydration: Intermediate step in creating retail products, inhibits microbial growth, cost-effective packaging and storage, and ready-to-eat foods (no refrigeration needed).

Other Preservation Techniques

  • Freezing: The process of converting a substance from a liquid to a solid state by removing heat.

  • Freezing Principles: Low temperatures inhibit reaction rates and microbial growth, and reduce moisture for growth. This also preserves taste, texture, and nutrients compared to other methods.

  • Freezing Methods & Equipment: Uses air blast, plate, or cryogenic freezing, and fluidized bed or spiral freezers.

  • Freezing Quality: Fast freezing creates small ice crystals for better texture; slow freezing creates larger crystals, causing loss of quality. Storage temperature needs to be maintained at low temperatures to prevent recrystallization. Food preparation methods like blanching are used to inactivate enzymes and packaging to prevent freezer burn.

  • Freezing Point Depression: Solutes lower the freezing point and causes water expansion, affecting volume and texture.

  • Irradiation: Exposing food to controlled ionizing radiation for preservation.

  • Irradiation Techniques: Gamma rays, electron beams, and X-rays.  Gamma rays and X-rays penetrate deeply, useful for packed food, while electron beams have lesser penetration, suitable for thin products.

  • Irradiation Mechanism: Damages microbial DNA, preventing reproduction, and altering cell membranes.  It affects food quality by breaking chemical bonds, impacting vitamins and proteins.

  • Contemporary Preservation Techniques: High Pressure Processing (HPP) uses pressure up to 900 MPa in liquid-submerged products to inactivate microorganisms. Pulsed Electric Field (PEF) uses high-voltage pulses for inactivation of pathogens in liquid foods. Ultrasound waves use sonic waves to damage membranes and cause bacterial death. Pulsed light uses high-energy light pulses for surface decontamination.

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