Food Preservation: Modified Atmosphere, Osmosis, and Filtration

Posted on Jan 11, 2025 in Chemistry

Food Preservation Techniques

Modified atmosphere conservation involves altering the air around food to maintain its quality. This can be done by replacing the air with a specific gas or mixture, or by removing it through vacuum sealing. This helps preserve the food’s chemical, structural, and microbiological properties.

Types of Modified Atmosphere Preservation

  • Vacuum Packaging: Removes air to prevent bacterial growth, lipid oxidation, and enzymatic changes. However, it can cause reversible color changes in meat and maintain aerobic metabolism in plants.
  • Modified Atmosphere Packaging (MAP): Replaces the air with a specific gas mixture tailored to the product. Common gases include:
    • N2 (Nitrogen): Inert, prevents oxidation, and inhibits aerobic organisms. It’s an alternative to vacuum packaging and prevents package collapse.
    • O2 (Oxygen): Maintains the color of fresh meat, supports aerobic metabolism in plants, inhibits anaerobic microorganisms, and promotes aerobic oxidation.
    • CO2 (Carbon Dioxide): Bacteriostatic and fungicidal, especially at high temperatures. It does not inhibit anaerobic organisms.

The gas mixture is chosen based on the product’s sensitivity to O2 and CO2, color stabilization needs, and the microorganisms to be inhibited.

Atmospheres Used in Food

  • Meat: CO2 is used to inhibit microorganisms, and O2 to maintain color.
  • Fish: Such as hake, tuna, and mackerel.
  • Fruits and Vegetables: To inhibit post-harvest growth.

Modified Atmosphere Packaging Process

MAP is often done in cold rooms with bulk products. The atmosphere is controlled to maintain its composition throughout storage, which can delay or accelerate fruit ripening.

Active Packaging

This involves adding substances to the packaging, such as:

  • O2 absorbers: Bags with metallic reducing agents like Fe.
  • CO2 absorbers.
  • Ethylene absorbers.
  • Moisture absorbers: Such as silica.
  • Sustained-release microbicides: Such as ethanol.

Osmosis and Reverse Osmosis

Osmosis: Water moves from a less concentrated to a more concentrated solution until equilibrium is reached. Only water flows, not solutes.

Reverse Osmosis: Water is forced to flow from a more concentrated to a less concentrated solution by applying pressure. This allows for the separation of molecules with similar molecular weights and requires high pressure.

Filtration Techniques

Conventional Filtration: The flow is perpendicular to the filter media, which can cause clogging. The filter needs to be changed frequently.

Membrane Filtration: The liquid flows parallel to the membrane surface, which retains particles by screening.

Membrane Filtration Types

  • Reverse Osmosis: Membranes only allow water to pass through, retaining almost all solutes. It requires higher pressures and has finer pores.
  • Ultrafiltration: Allows the passage of some solutes, requires less pressure, and has fewer pores.