Lecture Notes: The Effect of pH on Microbial Growth

pH Scale Overview

• Scale Range: 0 to 14
  • Neutral: pH 7
  • Acidic: pH < 7
  • Alkaline/Basic: pH > 7

Types of Microbial Preferences

• Acidophiles: Thrive in acidic environments
• Neutrophiles: Prefer neutral pH (~7)
• Alcaliphiles: Prefer alkaline conditions

Microorganisms and pH

• Diversity of Microorganisms: Can grow in various environments
• Relevant Microorganisms: Focus on those affecting humans and food
• Optimal pH for Most Bacteria: pH 6.5 to 7.5
  • Aligns with human body and environment
• Low pH Growth:
  • Few bacteria grow below pH 4
  • Acidophiles exist but aren't a concern for food/human health

Low pH as a Growth Inhibitor

• Microbial Growth Inhibition: Low pH inhibits most microbes, especially pathogens
• Fermentation as Preservation:
  • Fermentation lowers the pH through lactic acid production
  • Fermented foods (e.g., sauerkraut, kimchi, yogurt) are preserved due to low pH
  • Example: Sauerkraut can last years in a fridge without spoiling

Molds and Yeasts

• Preferred pH Range: 5 to 6

Microorganisms' Metabolism

• Production of Acidic Byproducts:
  • Microbes release acidic compounds during metabolism
  • Acidic byproducts lower the pH of their environment
  • This self-poisoning limits microbial overgrowth
  • Prevents Earth from being overrun by bacteria

Conclusion

• pH has a significant impact on microbial growth
• Understanding pH helps in food preservation and microbial management