Unit 5: Food Microbiology

Important Microorganisms in Food

Microbes in food can be categorized into three groups:

1. Beneficial ("The Good"): Microbes used in food production (fermentation).
   • Example: Lactobacillus in yogurt, Saccharomyces (yeast) in bread.
2. Pathogenic ("The Bad"): Disease-causing microbes that contaminate food.
   • Example: Salmonella, Listeria, Norovirus.
3. Spoilage ("The Ugly"): Microbes that cause food to rot, decay, and become undesirable.
   • Example: Pseudomonas, various molds.

Major Food-Borne Diseases

A food-borne illness is caused by consuming contaminated food or drink.

Food Infection vs. Food Intoxication

Bacterial Diseases

• Salmonellosis (Infection):
  • Cause: Salmonella bacteria.
  • Source: Contaminated poultry, eggs, and raw milk.
• Staphylococcal Food Poisoning (Intoxication):
  • Cause: Staphylococcus aureus (produces a heat-stable enterotoxin).
  • Source: Human skin (food handlers), creamy salads, cured meats.

Viral Diseases

• Norovirus:
  • Cause: Highly contagious Norovirus.
  • Source: Contaminated water, shellfish, or food handled by an infected person. The leading cause of foodborne illness outbreaks.
• Hepatitis A:
  • Cause: Hepatitis A virus (HAV).
  • Source: Contaminated food or water, often from fecal-oral route. Causes liver inflammation (jaundice).

Food Preservation

Food preservation techniques aim to slow down or stop microbial growth, extending the shelf life of food.

Fermented Foods

Definition: Fermentation

A metabolic process where microorganisms (like yeast and bacteria) convert carbohydrates (like sugar) into alcohol or acids in the absence of oxygen.

Humans have used fermentation for thousands of years, primarily as a method of preservation.

Examples of Fermented Foods:

• Yogurt/Cheese: Lactic Acid Bacteria (e.g., *Lactobacillus*) ferment lactose (milk sugar) into lactic acid. The acid coagulates milk protein and prevents spoilage.
• Bread: Yeast (Saccharomyces cerevisiae) ferments sugar, producing Carbon Dioxide (CO2) gas, which makes the dough rise.
• Wine/Beer: Yeast ferments sugars from grapes or grain into Ethanol (alcohol).
• Sauerkraut/Kimchi: Lactic Acid Bacteria ferment sugars in cabbage.

Importance of Fermented Foods

1. Preservation: The production of acid (lactic acid, acetic acid) or alcohol creates an environment where spoilage microbes cannot grow.
2. Enhanced Digestibility: Microbes partially break down complex compounds, making them easier for us to digest (e.g., fermenting milk into yogurt breaks down lactose).
3. New Flavors/Textures: Creates desirable new tastes and textures (e.g., cheese, beer, soy sauce).
4. Increased Nutritional Value: Microbes can synthesize new vitamins (like B vitamins).

Probiotics and their Potential Health Benefits

Definition: Probiotics

Probiotics are "live microorganisms which, when administered in adequate amounts, confer a health benefit on the host." (World Health Organization definition)

• What they are: These are "good" bacteria, most commonly strains of Lactobacillus and Bifidobacterium.
• Sources: Found in fermented foods like yogurt, kefir, kimchi, and also available as dietary supplements.

Potential Health Benefits:

• Digestive Health: Help maintain a healthy balance of gut microflora. Can be used to treat or prevent diarrhea (especially antibiotic-associated diarrhea).
• Immune System Support: The gut contains a large part of the immune system. A healthy gut microbiome can help modulate and support immune function.
• Improved Digestion: Can help break down food and absorb nutrients.
• Competitive Exclusion: "Good" probiotic bacteria can take up space and nutrients, making it harder for "bad" pathogenic bacteria to establish an infection.