Food preservation

Cards (39)

  • Removal of microorganisms
    • Method: Heat treatment, filtration, or chemical additives.
    • Example: Pasteurisation of milk to eliminate harmful bacteria.
  • Inhibiting growth of organisms
    • Method: Lowering temperature, reducing moisture, adjusting pH, or using preservatives.
    • Example: Refrigeration to slow down bacterial growth.
  • Removing oxygen
    • Method: Vacuum packing or canning.
    • Example: Canned foods where oxygen is removed to prevent oxidation and spoilage.
  • Modifying storage atmosphere
    • Method: Controlled or modified atmosphere packaging.
    • Example: Packaging with gases like nitrogen to slow down spoilage.
  • Drying
    • Method: Removing water content from food.
    • Example: Dried fruits and jerky, where moisture removal inhibits microbial growth.
  • Advantages of food preservation
    extends shelf life- canning and freezing
    Retains nutritional value- freeze drying fruits
    Enhances food safety- pasteurization kills bacteria
    Offers convenience- pre-packaged meals
    Seasonal availability- frozen berries
    Economical- buying bulk can be cost effective
    Variety and taste
  • Underlying principle of freezing
    • Basic Concept: Lowering the temperature of food to below its freezing point, typically -18°C or lower, to inhibit the growth of microorganisms and slow down enzymatic reactions that cause food spoilage.
    • Effect on Microorganisms: Freezing doesn't kill microorganisms but renders them inactive.
    • Effect on Food Quality: Slows down chemical changes and prevents spoilage.
  • Quick freezing
    • Explanation: Rapid freezing process that minimises the formation of large ice crystals, preserving the cellular structure and texture of food.
    • Effects: Better preservation of texture, taste, and nutritional value. Ideal for most fruits, vegetables, meats, and fish.
  • Slow freezing
    • Explanation: Gradual freezing process occurring at standard freezer temperatures.
    • Effects: Larger ice crystals form, potentially damaging cell structure, leading to a change in texture upon thawing. More suitable for less delicate items like baked goods.
  • Suitable foods for home freezing
    Fruits and veg- especially when blanched
    Meat and poultry- With proper packaging to prevent freezer burn
    Fish and seafood
    Baked goods
    Prepared meals
  • Unsuitable foods for home freezing
    High water content vegetables- can become soggy
    Dairy products- can separate
    Egg based sauces- separate and curdle
    Fried food- can be soggy
  • Advantages of home freezing
    Convenience- easy access
    Nutritional retention- freezing preserves vitamins and minerals
    Waste reduction
    Seasonal flexibility
  • Disadvantages of home freezing
    Freezer burn
    Energy consumption
    storage limitation
  • Preparation for home freezing
    Cleaning and cutting
    blanching
  • Blanching
    Briefly boiling vegetables, then plunging them into cold water. inactivates enzymes that cause spoilage and preserves colour flavour and nutrition
  • Packaging

    Freezer bags- prevent freezer burn
    Aluminium foil and plastic wrap
    Rigid containers
  • Thawing
    Refrigerator: slow but safe
    Cold water: faster than refrigerator
    Microwave: used when food will be cooked immediately after
    Precautions
    Temperature control: keep food at safe temperature to prevent bacterial growth
    Cross contamination
  • Blast freezing
    Food items placed in blast freezer. Rapid freezing forms smaller ice crystals which causes less damage to cell structures preserving texture and flavour.
  • Plate/contact reasoning

    Food place between metal plates that are cooled. Suitable for flat shaped products.
  • Underlying principles of canning and bottling
    • Sterilisation: Both canning and bottling involve sterilisation, where heat is used to destroy microorganisms that can cause spoilage or disease.
    • Airtight Sealing: Prevents recontamination and preserves the food for extended periods.
    • Heat Application: Varied based on the type of food, effectively destroys enzymes and microorganisms.
  • Stages of the canning process
    • Preparation: Food is cleaned, peeled, chopped, or prepared as necessary.
    • Filling: The prepared food is placed into cans or jars.
    • Air Removal: Air is evacuated to prevent oxidation and spoilage.
    • Sealing: Cans or jars are sealed to prevent contamination.
    • Sterilisation: The sealed containers are heated to destroy pathogens and spoilage organisms.
    • Labelling: Includes information about contents, nutritional value, and expiry date.
  • Methods of canning
    • aseptic- sterilisation of food & container separately, followed by aseptic packaging in a sterile environment.
    • High acid- Foods with a pH of 4.6 or lower, requiring lower temperatures for sterilisation.
    • low acid- Foods with a pH above 4.6, requiring higher temperatures for effective sterilisation.
  • Suitable food for canning
    Fruits and Vegetables: Due to their natural acidity.
    Meats and Poultry: Protein-rich and low-acid, requiring careful processing.
    Seafood: Including fish, requires specific canning techniques.
    Dairy Products: Processed under aseptic canning methods.
  • Dehydration
    • removal of water from food, leading to a significant reduction in moisture content.
    • Purpose: To extend the shelf life of food products by inhibiting microbial growth and enzymatic reactions that require water.
  • Methods of dehydration - Fluidised bed drying
    • hot air is passed through a bed of soil particle, causing them to act like a fluid.
    • The food particles are suspended in a hot air stream, allowing efficient and uniform heat transfer.
  • Methods of dehydration- accelerated freeze drying
    • involves freezing the food and then reducing the surrounding pressure to allow the frozen water in the food to sublimate directly from the solid to the gas phase.
    • Process: The food is first frozen solid and then placed in a vacuum chamber where the pressure is lowered, and heat is applied, allowing the ice to evaporate without passing through a liquid phase.
  • Methods of dehydration- sun drying
    • food is dried using natural sunlight and air.
    • Process: Food is spread out in thin layers and exposed to sunlight and air. Moisture evaporates due to solar heat and air movement.
  • Fermentation
    • metabolic process that converts sugar to acids, gases, or alcohol. It occurs in yeast and bacteria, and also in oxygen-starved muscle cells, as in the case of lactic acid fermentation.
    • Purpose: to preserve food by converting carbohydrates like sugars into alcohol or organic acids under anaerobic conditions.
  • Underlying principles of fermentation
    • Anaerobic Environment: Fermentation typically occurs in environments where oxygen is limited or absent.
    • Microbial Growth: Specific microorganisms, such as yeast or bacteria, are instrumental in the fermentation process. These microorganisms feed on the carbohydrates present in the food, producing alcohol, acids, and gases.
    • Preservation Mechanism: The acids or alcohol produced during fermentation act as natural preservatives, inhibiting the growth of harmful bacteria. This process also enhances the nutritional content and flavour of the food.
  • Types of fermentation
    • Alcoholic Fermentation: Yeasts convert sugars into alcohol and carbon dioxide. Used in making beer, wine, and spirits.
    • Lactic Acid Fermentation: Lactic acid bacteria convert sugars into lactic acid. This method is used in yoghurt, kefir, and fermented vegetables like sauerkraut and kimchi.
    • Acetic Acid Fermentation: Converts alcohol into acetic acid. A prime example is vinegar production.
  • Fermented food
    • Dairy Products: Yogurt, cheese, and kefir.
    • Vegetables: Sauerkraut, kimchi, and pickles.
    • Breads: Sourdough bread, where fermentation aids in rising.
    • Beverages: Wine, beer, and kombucha.
  • Irradiation
    • process of exposing food and food packaging to ionising radiation such as gamma rays, electron beams, or X-rays.
    • Purpose: Primarily used to preserve food, reduce the risk of foodborne illness, prevent the spread of invasive pests, and increase shelf life.
  • Underlying principle of irradiation
    • lonising Radiation: The process involves using high-energy radiation that penetrates food, destroying bacteria, viruses, and other pathogens without significantly raising the temperature or altering the nutritional and sensory attributes of the food.
    • Mechanism: The energy emitted by the radiation breaks chemical bonds and forms ions, disrupting the DNA of harmful organisms, effectively killing or inactivating them.
  • Irradiation
    • Legislation: Food irradiation is regulated and monitored by various national and international agencies to ensure its safe and appropriate use.
    • Radura Symbol: The international symbol for irradiated food, consisting of a green radial pattern, symbolising the irradiation process. The presence of the Radura symbol on packaging indicates that the product has been treated with ionising radiation.
  • Advantages of irradiation
    • Extended Shelf Life: Slows down ripening in fruits and vegetables, and prevents spoilage.
    • Food Safety: Effectively kills bacteria, parasites, and other pathogens, reducing the risk of illness.
    • Cold Pasteurisation: Acts as an alternative to traditional pasteurisation methods without using heat, preserving food quality.
    • Prevention of Invasive Pest Spread: Kills insects and parasites in foods, preventing the spread of non-native species.
    • Decreased Need for Chemical Preservatives: Reduces reliance on chemical additives for preservation.
  • Disadvantages of irradiation
    • Public Perception: Concerns and misconceptions about the safety and nutritional impact of irradiated foods.
    • Nutritional Changes: alterations in vitamins and nutrients.
    • Cost: The process can be more expensive than traditional preservation methods.
    • Packaging Considerations: Requires specialised packaging materials.
    Not Effective Against All Pathogens: Some microorganisms are resistant to irradiation.
  • Effects of freezing on food
    • Texture Changes: Formation of ice crystals can disrupt cell walls, altering texture in some foods, especially fruits and vegetables.
    • Nutritional Value: Generally well preserved, though some vitamin loss, particularly water-soluble vitamins like Vitamin C, can occur.
    • Flavour Preservation: Freezing maintains the flavour of most foods effectively, but spices may become more pronounced.
  • Effects of canning on food
    • Nutritional Changes: Some nutrients, especially heat-sensitive ones like vitamins B and C, can be lost during the heating process.
    • Texture Alterations: Softening of fruits and vegetables as heat breaks down cell walls.
    • Flavour Changes: Can enhance flavours in some foods, but can also lead to changes due to interactions with the canning liquid.
  • Effects of chemical preservation on food
    • Nutritional Impact: Minimal direct effect on nutrients, but some preservatives may interact with food
    • Safety Concerns: Some preservatives can cause allergic reactions or other health concerns in sensitive individuals.
    • Flavour and Color: Can affect the flavour and colour of some foods; for example, sulfites can prevent browning in dried fruits.