Control of Microbial Growth

Control of Microbial Growth

5.1 Approaches to Control

  • Principles of Control:

    • Sterilization

    • Disinfection

    • Pasteurization

    • Decontamination

    • Preservation

Locations of Application

  • Where is Control Applied?

    • Food Production Facilities

    • Water Treatment Facilities

    • Microbiology Labs

    • Hospitals

    • Daily Life

Influencing Factors in Selection of an Antimicrobial Procedure

  • Factors to consider:

    • Type and number of microbes present

    • Environmental conditions present

    • Risk of infection associated with the microbes

    • Composition of the infected item

5.2 Selection of an Antimicrobial Procedure

Heat as a Method of Control

  • Heat Characteristics:

    • Considered safe, relatively fast, inexpensive, and non-toxic

  • Types of Heat:

    • Moist Heat: Irreversibly denatures proteins

    • Boiling

    • Pasteurization:

      • Example: Milk is treated at 72°C for 15 seconds

    • Autoclaving:

      • Conditions: 121°C at 15 psi for 15 minutes

    • Commercial Canning

    • Dry Heat:

    • Less effective than moist heat, requires longer times at higher temperatures

    • Example: 200°C for 90 minutes

    • Common methods: Hot air ovens, Incineration

Autoclave Components

  • Components of an Autoclave:

    • Safety valve

    • Control valve (regulates steam to chamber)

    • Exhaust valve (removes steam after sterilization)

    • Pressure gauge (measures pressure)

    • Door (seals the autoclave)

    • Air thermometer (monitors temperature)

    • Pressure regulator (maintains optimum pressure)

    • Steam supply

    • Trap (for condensation)

    • Jacket steam

5.3 Destroying Microorganisms and Viruses: Heat

  • Heat is a primary method for destroying microorganisms and viruses.

5.4 Physical Methods of Control

  • Filtration:

    • Examples:

    • Membrane filters

    • HEPA filters

  • Radiation: A technique used to control microbial growth.

  • High Pressure: Utilized as a microbial control method.

5.5 Chemicals Used in Antimicrobial Activity

  • Potency categorization of Chemicals:

    • Sterilants

    • High-level disinfectants

    • Intermediate-level disinfectants

    • Low-level disinfectants

Chemical Selection Criteria

  • Factors for selecting chemicals:

    • Toxicity

    • Activity

    • Compatibility with materials

    • Cost

    • Storage requirements

    • Environmental risk assessment

Common Chemical Classes and Examples

  • Types of Chemicals Used:

    • Alcohols

    • Aldehydes

    • Ethylene oxide:

    • A gaseous sterilant suitable for laboratory items

    • Halogens

    • Metal compounds

    • Ozone:

    • Applied in disinfecting drinking and wastewater

    • Peroxygens

    • Phenolics:

    • Example: Triclosan

5.6 Preservation of Perishable Products

  • Methods of Preservation:

    • Low-temperature storage:

    • Techniques: Refrigeration and Freezing

    • Chemical preservatives:

    • Example: Weak organic acids (benzoic acid, sorbic acid)

    • Other examples: Nitrates and nitrites (used in processed meats)

Reducing Available Water in Food

  • Methods of water reduction:

    • Salting

    • Sugaring or Drying food

    • Lyophilization:

    • Also known as freeze-drying.