Food as substrate

• What serves as a nutrient source for both humans and microorganisms?


  Food
• What are the two types of microbes associated with food?

  Beneficial and harmful microbes
• What are the effects of microbial growth in food?


  • Improve food quality (e.g., fermentation)
  • Cause spoilage
  • Transmit diseases
• What is the intrinsic factor related to nutrient content in food?


  Carbohydrates, proteins, vitamins, and minerals
• What role do carbohydrates play in microbial growth?


  They serve as an energy source
• How do sugars affect microbial growth?


  They promote yeast and bacterial growth
• What is the role of starch in microbial growth?


  It supports mold growth
• Why are proteins important for microbial growth?


  They provide a nitrogen source
• What do vitamins and minerals contribute to microbial metabolism?


  They are essential for microbial metabolism
• How does pH affect microbial growth?


  It affects microbial enzyme activity and growth
• What is the optimal pH range for most bacteria?


  Near neutral (6.5-7.5)
• What pH range do yeasts thrive in?


  Slightly acidic (4.5-6.0)
• What is the pH range that molds can tolerate?


  Wide range (3.0-8.0)
• Why do acidic foods generally resist bacterial growth?


  Because their pH is below 4.6
• What is the pH of citrus fruits?


  Between 2.0 and 4.0
• What does water activity (a\(_w\)) measure?


  The vapor pressure of a solution compared to pure water
• What is the general water activity requirement for bacteria?


  Generally > 0.91
• At what water activity can molds grow?


  As low as 0.80
• What is the water activity range for yeasts?


  Intermediate between bacteria and molds
• What is the water activity of S. aureus?


  Can grow at a\(_w\) of 0.86
• What is the water activity requirement for C. botulinum?


  Requires a\(_w\) > 0.94
• What does the oxidation-reduction potential (Eh) measure?


  A food's tendency to gain or lose electrons
• How does Eh affect microbial growth?


  It affects the growth of aerobic, facultative, and anaerobic microbes
• What does a positive Eh value indicate?


  Oxidized state (favors aerobes)
• What does a negative Eh value indicate?


  Reduced state (favors anaerobes)
• What type of microbial growth does fresh meat surface support?


  Aerobic growth
• What are some natural antimicrobials found in foods?


  • Plant essential oils (e.g., eugenol in cloves, allicin in garlic)
  • Milk components (e.g., lactoferrin, lactoperoxidase system)
  • Egg components (e.g., lysozyme, conalbumin)
  • Plant phenolics (e.g., hydroxycinnamic acid derivatives)
• What are the extrinsic factors affecting microbial growth?


  • Temperature
  • Relative humidity (RH)
  • Gases
  • Microbial interactions