Unit 4 Food Microbiology final

Unit 4: Food Microbiology

Microorganisms in Food

  • Microbiology: Study of microscopic plants and animals

  • Five important groups in food industry:

    • Viruses

    • Bacteria

    • Molds and Yeast (Fungi)

    • Algae

    • Protozoa

  • Classification:

    • Spoilage Organisms (e.g., mold)

    • Pathogens (e.g., Salmonella, Hepatitis A)

Types of Microbes (Microorganisms)

Viruses

  • Parasitic and cannot be cultivated outside host cells.

  • Infect living cells of plants and animals.

  • Very small; observed only under an electron microscope.

  • Latch onto host cells, inject nuclear material, replicate, and burst cell releasing new viruses.

  • Bacteriophages: Viruses that infect bacteria.

  • Mycophages: Viruses that infect fungi.

  • Harmful Effects:

    • Can affect bacteria used in cheese and yogurt production.

    • Cause diseases like poliomyelitis and infectious hepatitis through contaminated food/water.

Fungi

  • Includes molds and yeasts.

    • Molds:

      • Multicellular, aerobic, and chlorophyll-free.

      • Produce thread-like filaments (hyphae) forming branched mycelium.

      • Grow on most foods regardless of moisture, acidity, or salt/sugar concentrations.

      • Optimal growth temperature: 20-30˚C; can grow at lower temperatures (some as low as 10˚C).

      • Reproduce by asexual spores; harmful molds produce toxins (e.g., aflatoxin).

    • Yeasts:

      • Unicellular fungi, reproduce by budding.

      • Prefer slightly acidic foods; require moisture levels >20%.

      • Used in bread, beer, and vinegar production, can spoil jam and fruits.

Pathogenic Microorganisms

  • Protozoa: Single-celled, essential to the food chain.

    • Pathogenic; e.g., Entamoeba histolitica (amoebic dysentery).

  • Algae:

    • Photosynthetic, some pathogenic algae can contaminate shellfish.

Bacteria

  • Prokaryotic, unicellular microorganisms found everywhere.

  • Classified as Gram-positive or Gram-negative; shaped as rods, spheres, spirals.

  • Beneficial for food by fermenting dairy products (e.g., cheese, yogurt).

  • Bacterial cell components:

    • Capsule: Layer outside the cell wall.

    • Cell wall: Thin protective layer.

    • Flagellum: For propulsion.

    • Pili: Allow adherence to surfaces.

  • Safety and Spoilage Risks:

    • Pathogenic bacteria cause food poisoning; can multiply rapidly under ideal conditions.

Food Spoilage and Contamination

  • Microbial action, physical changes, natural enzymes, and chemical reactions can spoil food.

  • Types of contamination:

    • Microbiological (pathogens)

    • Physical (foreign objects)

    • Chemical (residues)

Food Preservation Strategies

  • High Temperatures: Control growth, eliminate pathogens (e.g., pasteurization, sterilization).

    • Pasteurization: Reduces spoilage organisms.

    • Sterilization: Destroys all microorganisms and spores.

  • Low Temperatures: Slower growth, some organisms can survive; used for refrigeration and freezing.

  • Dehydration: Inhibits microbial activity by reducing water activity (aw).

    • Methods: Sun drying, mechanical drying, freeze-drying.

  • Chemical Preservation: Food additives like nitrites/nitrates, organic acids, and preservatives control spoilage.

Beneficial Roles of Microorganisms

  • Used in food production (e.g., yogurt, cheese).

  • Sources of nutrients and vitamins (e.g., vinegar, fermented foods).

  • Improve soil fertility in agriculture.

Conclusion

Understanding food microbiology is crucial for food safety and preventing contamination. Awareness of the role of specific microorganisms in spoilage versus fermentation can help in managing food preparation and storage.