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Food Spoilage: “Stinkies”, “Slimies” and Biofilms. -by- Jovana Kovačević. October 22, 2009. Outline. Spoilage of Food Spoilage Signs Meat, Fish, Dairy What do laboratory tests tell you about spoilage? Biofilms Properties and formation Why are they a problem?

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food spoilage stinkies slimies and biofilms

Food Spoilage:“Stinkies”, “Slimies” and Biofilms


Jovana Kovačević

October 22, 2009

  • Spoilage of Food
      • Spoilage Signs
      • Meat, Fish, Dairy
      • What do laboratory tests tell you about spoilage?
  • Biofilms
      • Properties and formation
      • Why are they a problem?
  • How do we deal with spoilage and biofilms?
food spoilage
Undesirable deterioration of food quality that may result in changes in odor, taste and appearance of food.Food Spoilage
food spoilage4
Food Spoilage
  • Types of spoilage:
      • Microbial:
        • Bacteria, yeasts, molds
      • Non-microbial
        • Foreign materials, enzymes
  • Changes not necessarily harmful
microbial food spoilage
Microbial Food Spoilage
  • Each food unique microbial environment
    • unique spoilage agents for each
  • Why do microorganisms spoil our food?
    • food composition ideal source of nutrients for microbes
    • availability of water and oxygen
    • suitable pH
  • Factors that affect spoilage:
    • Oxygen, temperature, pH, aw, humidity
spoilage organisms
Spoilage organisms
  • Similar microflora emerge in different foods under the same conditions
  • Affected by the:
      • Type of food
      • Processing
      • Preservation
      • Storage conditions
  • Domination of specific spoilage microbes:
      • Initial counts present
      • Nutrient composition
      • Chemical and physical parameters
spoilage signs
Spoilage Signs
  • Odor:
    • Breakdown of proteins – putrefaction

e.g. “rotten egg” smell

  • Sliminess
  • Discoloration
    • Mold on bread, blue and green mold on citrus fruit and cheese
spoilage signs8
Spoilage Signs…
  • Souring
    • Production of acid

e.g. sour milk from production of lactic acid

  • Gas formation
    • Meat becomes spongy
    • Swollen or bubbling packages and cans
food types based on rate of spoilage
Food Types: Based on rate of spoilage

1) Highly perishable

  • meat
  • fruit
  • milk
  • vegetables
  • eggs

2) Semi perishable

  • potatoes
  • nuts

3) Stable

  • rice
  • flour
  • dry beans



common causes of food spoilage
Common Causes of Food Spoilage
  • Inadequate storage temperatures
  • Prolonged storage times
  • Improper ventilation
  • Cross contamination
  • Excessive delays between receiving and storing
  • Inadequate food safety standards
meat spoilage12
Meat spoilage…
  • Cutting board contamination
  • Conveyor belts
  • Temperature
  • Delay between storage and distribution
  • Fecal contamination from intestines
fish and eggs spoilage continued

Polluted waters

Transportation vehicles, boxes

Poultry and Eggs

Human contact

Penetration by bacteria


Fish and Eggs Spoilage Continued




spoilage of milk and dairy products
Spoilage of Milk and Dairy Products

spoilage of fruits and vegetables
Spoilage of Fruits and Vegetables

examples of food quality tests
Examples of Food Quality Tests
  • Meat & Fish: pH for vacuum packaging (< 6.0)
  • Visual inspection for leakage / color change
    • Faulty seals, pin-holes
  • Sensory test
  • Aerobic plate count at 30°C
    • Indication of hygiene at packaging
    • Expected refrigerated shelf-life
    • ↑ APC = improper cleaning of equipment, unacceptable time/temperature history of raw products
testing for microbial quality
Total Viable Count



Escherichia coli



Bacillus spp.

Clostridium perfringens

Lactic acid bacteria

Pseudomonas species

Yeasts and molds

Testing for Microbial Quality
total viable count
Total Viable Count
  • Total Viable Count also known as:
    • Heterotrophic plate count (HPC)
    • Aerobic plate count (APC)
    • Total plate count (TPC)
    • Aerobic colony count (ACC)
    • Aerobic mesophilic count
  • Purpose:

The aerobic plate count gives the total number of bacteria able to grow in an oxygenated or aerobic environment.

  • Cooked foods should have little to no bacteria present
  • Result provides a guide for shelf-life of foods
    • The higher the count: prolonged storage, and/or inadequate cooking.

Note: Not a useful indicator for fermented foods or fresh ready-to-eat raw fruits and vegetables.

  • A family of Gram-negative, facultatively anaerobic, rod-shaped bacteria that do not form endospores and ferment variety of sugars
  • Includes:
    • Pathogenic microbes:

e.g. pathogenic E. coli, Proteus, Salmonella, Shigella, Yersinia, Enterobacter, Serratia, Klebsiella

    • Non-pathogenic microbes:

e.g.Citrobacter, Erwinia, Hafnia

coliforms and e coli
Coliforms and E. coli
  • Coliforms:
    • Total coliforms
    • Fecal coliforms:
      • Found in human and animal intestinal wastes
      • More precise indicator of the presence of sewage contamination than total coliforms
    • Four groups of fecal coliforms:
      • Enterobacter
      • Klebsiella
      • Escherichia
      • Citrobacter
escherichia coli
Escherichia coli
  • Best indicator of fecal sanitation problems
  • Characterized by the fermentation of glucose and lactose
  • Found
    • In the gut of warm blooded mammals
    • In the gut of insects and reptiles
    • As natural soil microbial flora
aerobic plate count environmental swabs
Aerobic Plate Count: Environmental Swabs

Guidelines for interpretation of bacterial counts from swabs and sponges as means of monitoring the cleanliness of surfaces.

** Values will vary depending on size of the surface area sampled. To calculate the number of bacteria per cm2 take the total CFU and divide by the surface area swabbed.

common spoilage microorganisms
Common Spoilage Microorganisms
  • Shewanella putrefaciens
  • Pseudomonas spp.
      • Gram negative
      • Rod shaped
      • Motile
      • Aerobic
      • Non-spore forming
      • Biofilm formers



Pseudomonas aeruginosa


“Variety of microorganisms arranged in a complex relationship to one another and embedded in a mass of extracellular polysaccharides of their own making”


biofilms continued
Biofilms Continued
  • Communities of bacteria adhering to:
      • Environmental surfaces
      • Living tissues
      • Indwelling medical devices
      • Industrial or potable water system piping
      • Natural aquatic systems
      • Food processing facilities:
        • Floors, waste water pipes, bends in pipes, rubber seals, conveyor belts, stainless steel surfaces (Kumar and Anand, 1998)

FEMS Microbiology Letters. 228:203-210.

why do bacteria form biofilms
Why do bacteria form biofilms?
  • Protection from the environment
      • Sanitizers
      • Antibiotics
  • Nutrient availability and metabolic cooperativity
  • Acquisition of new genetic traits
biofilm formation
Biofilm formation

control of microbial spoilage
Control of Microbial Spoilage
  • Good manufacturing practices
  • Cleaning and sanitation
    • Processing environment
    • Equipment
  • Handling with minimal physical damage
  • Washing (in some case)
  • Proper storage temperature
  • Rapid movement of food through processing plant
  • Treatments…
    • preservation
food preservation
Food preservation
  • Temperature based:
      • Chilling
      • Refrigeration
      • Freezing
      • Pasteurization
      • Canning
  • Water activity reduction
      • Dehydration
      • Addition of salts and sugars
  • Irradiation
  • Modified Atmosphere Packaging
  • Fermentation
  • Treatment with chemicals
      • Sorbic acid, phenylphenates, diphenyl and iodophors, fumigation with sulfur-containing dusts

1. Davey and O’Toole (2000). Microbial Biofilms: from ecology to molecular genetics. Microbiol. Molec. Bio. Rev. 64(4):847-867.

2. Forsythe, S.J, and P.R. Hayes. 1998. Food Hygiene Microbiology and HACCP. 3rd Ed. pp. 434. Aspen Publishers Inc., Maryland.

3. ICMSF. 2005. Microorganisms in Foods. Microbial Ecology of Food Commodities. 2nd Ed. pp. 763. Kluwer Academic/Plenum Publishers, New York, NY.

4. Marsh, E.J., H. Luo, H. Wang. 2003. A three-tiered approach to differentiate Listeria monocytogenes biofilm-forming abilities. FEMS Microbiology Letters. 228:203-210.