Handout B

• Approaches to Shelf Life Determination

  • Direct shelf life determination and monitoring
  • Accelerated shelf life estimation
• Spoilage of Food Products

  • Meat products
  • Seafoods
  • Dairy products
  • Egg
  • Vegetable and Fruit Products
  • Cereals, flour, and bakery products
• Bakery Products

  • Commercially produced bread – Molds
  • Homemade breads – Ropiness (e.g. B. subtilis)
  • Cakes – Molds
• Accelerated Shelf Life Estimation


  • Performed to meet product launch dates
  • Storage temperature is raised to increase the ageing process
• Challenge Tests


  • Samples are incubated under conditions that reproduce the large-scale food production and storage period
  • May be inoculated with specified target organisms of interest (e.g. Clostridium sporogenes)
• Indicator Organisms

  • Provide indirect evidence concerning a particular feature in the past history of the sample
  • e.g. fecal contamination or inadequate heat treatment
  • Index organism – Indicated the possible presence of an ecologically similar pathogen
  • Often employed to assess food safety and hygiene than quality
• Module 3: Spoilage- and Disease-Causing Microorganisms

  • Spoilage Mechanisms of Different Food Products
  • Causative Agents of Diseases and Associated Food Vectors
• Microbiological Determination of Shelf Life

  • Storage trials
  • Challenge tests
  • Predictive modelling
• Direct Shelf Life Determination and Monitoring

  • Applicable for products with short shelf lives
  • Batches of samples to be taken at specified stages in the development of the product
  • Samples are stored under controlled conditions until their quality becomes unacceptable
  • Tested for smell, texture, flavor, color, and viscosity
• Shelf Life is the time between the production of the product and the point at which the product becomes unacceptable to the consumer
• Cereals and Flour

  • High in proteins and carbohydrates
  • Low aw restricts growth of all microorganisms if stored properly
  • e.g. Bacillus and molds
• Chemical Indicators of Spoilage

  • Depletion of glucose (e.g. red meat)
  • Production of gluconic and 2-oxogluconic acid (e.g. beef)
  • Production of L- and D-lactic acids, acetic acid, and ethanol (e.g. pork and beef)
  • Biologically active amines (e.g. Tyramine in vacuum packed beef)
  • Volatile compounds (e.g. Proponol in beef)
• Storage Trials

  • Samples are taken at timed intervals and analyzed for: Total microbial load, Specific spoilage organisms (e.g. Pseudomonads, LAB), Viable counts are compared with sensory evaluation of the product
• Predictive Modelling


  • Simultaneously predict the growth of microorganisms over a range of conditions
  • Validate the model using published and in-house laboratory data
• Causative Agents of Diseases and Associated Food Vectors

  • Indicator Organisms
  • Foodborne pathogens and agents
• Characteristics of a Food Safety Indicator

  • Easily and rapidly detectable
  • Easily distinguishable from other members of the food flora
  • Have a history of constant association with the pathogen whose presence it is to indicate
  • Always present when the pathogen of concern is present
  • Density correlates with the pathogen of concern
  • Growth requirements and growth rate are equal
• Enterobacteriaceae

  • Gram-negative bacilli and facultative anaerobes
  • Includes Escherichia, Salmonella, Shigella, Yersinia, and Enterobacter
  • Indicators of enteric pathogens
• Common Indicator Organisms

  • Coliforms
  • Enterobacteriaceae
  • Enterococci
  • Bacteriophages
• Campylobacter

  • Gram-negative
  • Sporadic and self-limiting gastroenteritis
  • Includes C. jejuni (80% of cases) and C. coli (15%)
  • Found in raw chicken, beef, milk, mushrooms, clams, hamburger, water, cheese, pork, shellfish, eggs, cake icing
• Bacteriophages


  • Indicator of waterborne viruses
  • Present in human fecal matter
  • Plaque enumeration using agar overlay technique with a tester bacterial strain
• E. coli

  • Gram-negative
  • Includes Enteropathogenic E. coli (EPEC) causing diarrhea in infants
  • Enterotoxigenic E. coli (ETEC) causing "Traveler’s diarrhea"
  • Enteroinvasive E. coli (EIEC) causing Shigellosis-like symptoms
  • Shiga toxin-producing E. coli (STEC) causing hemorrhagic colitis and hemolytic uremic syndrome
  • O157:H7 strain is of major concern, found in ground beef, poultry, apple cider, raw milk, vegetables, cantaloupe, hot dogs, mayonnaise, salad bar items
• Foodborne Pathogens and Agents

  • Bacteria
  • Viruses
  • Parasites
  • Toxins
  • Prions
• Shigella

  • Gram-negative
  • Causes Shigellosis with bloody/non-bloody diarrhea
  • Found in salads, raw vegetables, bakery products, sandwich fillings, milk, dairy products, poultry
• Salmonella


  • Gram-negative
  • Causes gastroenteritis, enteric fever, and invasive systemic disease
  • Found in raw poultry, meat, eggs, milk and dairy products, vegetables, fruits, chocolate, coconut, peanuts, fish, shellfish
• Coliforms

  • Gram-negative, rod-shaped facultatively anaerobic bacteria
  • Fermentation of lactose to acid and gas within 48 hours at 45°C
  • Indicator of: Fecal contamination, Enteric pathogens, Post-processing contamination
  • Includes Escherichia, Klebsiella, Enterobacter, and Citrobacter
  • E. coli is the best indicator of fecal contamination
• Characteristics of a Food Safety Indicator

  • Density correlates with the pathogen of concern
  • Growth requirements and growth rate are equal to that of the pathogen
  • Persists slightly longer than the pathogen of concern (Die-off rate parallels that of the pathogen)
  • Absent from foods that are free of the pathogen (Except at certain minimum numbers)
• Enterococci

  • Indicator of fecal contamination in water
  • E. faecalis from human feces, E. faecium from human and animal feces
  • Indicator of hygienic quality for frozen, dried, and heat-treated food
  • Die more slowly than E. coli, more resistant to drying than coliforms
  • May survive better than pathogens so detection may have little consequence
• Foods associated with concern

  • Ground beef, poultry, apple cider, raw milk, vegetables, cantaloupe, hot dogs, mayonnaise, salad bar items
• Types of Shigella

  • S. sonnei, S. flexneri, S. dysenteriae, S. boydii
• Types of Vibrio

  • V. cholerae, V. parahaemolyticus, V. vulnificus
• Brucella causes Brucellosis which includes symptoms like sweating, headache, lack of appetite, fatigue, and fever
• Shigella causes Shigellosis which can lead to bloody/non-bloody diarrhea
• Types of Brucella

  • B. abortus (cattle), B. suis (swine)
• Food sources of Cronobacter

  • Powdered infant formula, plant-based ingredients, vegetables and salads
• Type of Plesiomonas

  • P. shigelloides
• Listeria monocytogenes causes Listeriosis which includes meningitis and sepsis
• Aeromonas causes Gastroenteritis and is found in seafood, snails, and drinking water
• Vibrio is gram negative
• Plesiomonas is gram negative
• Flaccid Paralysis is a neurological condition characterized by weakness or paralysis, reduced muscle tone or hypotonia