Revision

• Microbes


  Microscopic living things in/on food
• Microbe multiplication


  1. Occurs during handling, processing, packaging

  2. Increases as food quality decreases
• Enumeration


  Microbiologists count the numbers of microorganisms present in a food sample
• Isolation and identification


  Food microbiologists isolate and identify the organisms present in the food sample
• Liquid foods


  Non-viscous liquids measured with pipettes, viscous liquids weighed
• Solid food


  Weigh sample
• Sponge


  Swabbing a defined area
• Viable cells


  Fully competent cells that readily produce colonies
• Sub-lethally injured cells


  May not be recovered if selective agents are present in recovery media, selective agents act as a further stress
• Viable but non-culturable cells

  State most often induced by nutrient limitation
• Food environment testing


  Walls, floors and work surfaces
• RODAC


  Replicate organism detection and counting
• Enterobacteriaceae


  Large family of bacteria that cause foodborne illness, gram negative rods, oxidase-negative, facultative anaerobes, ferment glucose
• Colony morphology


  Size, shape, colour
• MacConkey agar


  Nutrition: pancreatic digest of gelatin and peptones, Selective: crystal violet and bile salts, Differential: neutral red pH indicator
• Microbial and non-microbial causes of food spoilage include colour defects, changes in texture, odours and development of slime
• Carbohydrate-rich, high moisture foods


  Molds produce enzymes that weaken skin of fruit, then bacteria can colonize
• Denser carbohydrates


  Also susceptible to mold growth
• Unpasteurized milk


  Opaque liquid, Lactococcus lactis overgrows and produces acid, then yeasts and molds predominate, protein digesting bacteria become active, resulting in bitter taste and clear coagulation
• Water activity


  Measure for the amount of available water, Aerobic microorganisms have +ve Eh values, Anaerobic microorganisms have -ve Eh values
• Grinding foods increases surface area
• Antimicrobial substances


  • Coumarins (fruit and veg)
  • Lysozymes (eggs)
  • Aldehydic and phenolic compounds (herbs and spices)
• Temperature


  Influences growth of microorganisms in muscle foods, below optimum growth, lag time and generation time are extended, microbial growth slows
• Foodborne illness


  Any disease of an infectious or toxic nature caused by, or thought to be caused by, the consumption of food or water, transmitted via the fecal-oral route (5Fs: feces, fingers, food, fomites and flies)
• Mycotoxins


  Fungus-derived toxins, secondary metabolites, can cause acute poisoning to long-term effects like immune deficiency and cancer
• Foodborne infection


  Ingestion of pathogen followed by growth in host
• Foodborne intoxication


  Ingestion of a pre-formed toxin already present in food, or exotoxin released into the food during pathogen growth and metabolism
• Reasons for emergence or re-emergence of foodborne illness

  • Mass production and globalisation of food supply
  • International movement of people
  • Changing character of the population
  • Lifestyle changes
  • Microbial evolution
• Food preservation


  Process of treating and handling food to stop or slow down spoilage and prevent foodborne illness while maintaining nutritional value, texture and flavour
• Shelf life


  Period of time a food product will remain safe to eat, retain desired characteristics, and comply with label nutritional data when stored under recommended conditions
• Use-by date


  Can be eaten until but not after
• Best before date


  Safe to eat after this date but may not be at its best
• Low temperature preservation


  Slows and prevents microbial growth, reduces metabolic reactions, increases lag time and generation time, decreases growth rate, stops cell division as temperature approaches minimum for growth
• Reduction in water activity

  Affects ability of microorganisms to grow in food, via drying/dehydration or addition of salts and sugar
• High temperature preservation


  Kills some or all microorganisms
• Pasteurization


  Heating food to a temperature that kills disease-causing microorganisms and substantially reduces numbers of spoilage organisms, based on water, salts, pH and proteins
• Sterilization


  Destruction of all viable organisms, includes UHT pasteurization and canning (heated in retorts, rapidly cooled)
• Vacuum packaging


  Air is removed
• Modified atmosphere packaging (MAP)

  Mixture of natural gases (N, CO2, Ar) in controlled proportions to displace oxygen and inhibit aerobic spoilage, but some pathogens and anaerobes can still grow
• Chemical preservatives


  • Acetic acid (vinegar)
  • Benzoic acid (cranberries)
  • Sorbic acid (Rowan berries)
  • Propionic acid
  • Sulphur dioxide (fruit and veg)
  • Sodium nitrate (cured meats)