Food Spoilage

Spoilage: Basics - The Rotten Truth

• Food spoilage: Undesirable alterations in food (odor, flavor, texture, appearance) rendering it unacceptable for consumption.
• Primary Causes:
  • Microbial growth (bacteria, yeasts, molds)
  • Enzymatic activity (autolysis)
  • Chemical reactions (e.g., oxidation)
  • Physical damage
• Key Factors Influencing Spoilage:
  • Intrinsic: pH, water activity ($a_w$), nutrients, antimicrobial compounds.
  • Extrinsic: Temperature, relative humidity, gaseous atmosphere.
• Manifestations: Changes in color, texture (e.g., slime), odor (e.g., putrid, sour), taste, gas production.

⭐ Many food spoilage organisms themselves are not pathogenic, but they can produce conditions favorable for the growth of pathogens or produce toxic metabolites.

Growth Factors - Recipe for Ruin

Spoilage depends on:

• Intrinsic Factors (Food-related):

  • pH: Bacteria prefer neutral ($\approx \textbf{7.0}$); molds/yeasts wider range (pH $\textbf{2-9}$).
  • Water Activity ($a_w$): Free water for growth.
  • Nutrients: C, N sources, vitamins.
  • Eh (Redox): Aerobes (+Eh), Anaerobes (-Eh).
  • Antimicrobials: Lysozyme, essential oils.
  • Biological Structures: Peels, shells.

• Extrinsic Factors (Environment-related):

  • Temperature: Psychrophiles ($<\textbf{20}°C$), mesophiles ($\textbf{20-45}°C$), thermophiles ($>\textbf{45}°C$). (📌 PMT: Psychro, Meso, Thermo)
  • Relative Humidity (RH): Affects surface $a_w$.
  • Gaseous Atmosphere: O2 for aerobes; CO2 in MAP.

⭐ Water activity (aw) is a critical intrinsic factor. Most spoilage bacteria need aw > 0.90. Xerophilic molds can grow at aw as low as 0.60.

Spoilers & Foods - Culprit Catalog

• Bacteria:
  • Pseudomonas: Psychrotroph; refrigerated meat, fish, milk (slime, green/fruity/putrid odors).

    ⭐ Pseudomonas species are notorious psychrotrophic spoilers of refrigerated proteinaceous foods like meat and milk, often causing slime formation and off-odors (e.g., fruity, putrid).

  • Bacillus: Cereals (ropy bread - stringy), canned foods (flat sour).
  • Clostridium: Anaerobe; canned foods (swelling, gas), meats (putrefaction).
  • Lactic Acid Bacteria (Lactobacillus, Leuconostoc): Dairy (souring), vacuum-packed meats (greening, slime), beverages (turbidity, acidity).
  • Erwinia: Fruits, vegetables (pectinolytic soft rot).
  • Alcaligenes: Dairy (ropy milk, bitterness).
• Yeasts:
  • Saccharomyces: Juices, syrups, wine (fermentation, CO₂).
  • Zygosaccharomyces: Osmophilic; high sugar foods (jams, honey).
  • Debaryomyces: Halophilic; salted meats, brines, cheese.
  • Candida: Dairy surfaces, butter, salads (films, yeasty off-flavors).
• Molds: (Visible growth, mycotoxins potential)
  • Aspergillus, Penicillium: Bread, cheese, fruits, nuts (blue/green/black molds).
  • Rhizopus, Mucor: Bread ("bread mold" - black, fuzzy), fruits, vegetables (soft rot).
  • Botrytis cinerea: Grapes, berries, vegetables ("grey mold" rot).
  • Byssochlamys: Heat-resistant ascospores; canned fruits (disintegration).

High‑Yield Points - ⚡ Biggest Takeaways

• Psychrotrophs (Pseudomonas, Listeria) spoil refrigerated foods.
• Molds (Aspergillus, Penicillium) spoil low water activity foods like bread, cheese.
• Yeasts (Saccharomyces, Candida) spoil high sugar/acid foods like juices, jams.
• Lactic acid bacteria (Lactobacillus) cause souring in dairy and meats.
• Flat sour spoilage in cans: Geobacillus stearothermophilus (acid, no gas).
• Sulfide stinker spoilage in cans: Desulfotomaculum nigrificans (produces H2S).
• Ropiness in bread: Bacillus subtilis (slime production).