Bacteria in Food Science

Bacteria are unicellular microorganisms found everywhere, including soil, water, air, and food. They play both beneficial and harmful roles in food processing and spoilage.

Types of Bacteria in Food

• Beneficial Bacteria (Probiotics): Used in fermentation and food preservation. Examples:
  • Lactobacillus: Used in yogurt, pickles, and sauerkraut production.
  • Streptococcus thermophilus: Used in dairy fermentation.
  • Bifidobacterium: Promotes gut health.

• Spoilage Bacteria: Cause deterioration of food quality without making it harmful. Examples:
  • Pseudomonas: Spoils milk, meat, and seafood.
  • Bacillus subtilis: Causes ropiness in bread.
  • Lactobacillus: Can cause souring in milk and vegetables.

• Pathogenic Bacteria: Cause foodborne illnesses. Examples:
  • Salmonella: Found in poultry, eggs, and raw meat, causing salmonellosis.
  • Escherichia coli (E. coli): Can lead to severe food poisoning (E. coli O157:H7).
  • Listeria monocytogenes: A concern in ready-to-eat foods, dairy, and meat.
  • Clostridium botulinum: Produces botulinum toxin, causing botulism.

Growth Conditions of Bacteria Bacteria thrive under specific conditions, known as FAT TOM:

1. Food: Prefer protein-rich foods like meat, dairy, and eggs.
2. Acidity: Grow best at neutral pH (4.6–7.5).
3. Temperature: Most pathogenic bacteria grow between 5°C and 60°C (danger zone).
4. Time: Bacteria can double every 20 minutes under optimal conditions.
5. Oxygen: Some bacteria require oxygen (aerobic), while others grow without it (anaerobic).
6. Moisture: Higher water activity (aw > 0.85) promotes bacterial growth.

Control Methods of Bacteria

1. Temperature Control: Refrigeration (< 4°C), freezing (-18°C), pasteurization (72°C for 15 sec), and sterilization.
2. pH Adjustment: Acidification using vinegar or citric acid.
3. Moisture Reduction: Drying, dehydration, or adding salt/sugar.
4. Proper Hygiene: Clean surfaces, utensils, and hands.

2. Yeasts in Food Science

Yeasts are unicellular fungi, larger than bacteria, with the ability to ferment sugars into alcohol and carbon dioxide. They can spoil food or be used in fermentation.

Characteristics

• Size: 5–8 µm in diameter, oval, spherical, or elliptical cells.
• Reproduction: Primarily by budding; some reproduce by fission.
• Growth Conditions:
  • pH: Wide range of 3.5 to 8.0.
  • Temperature: Optimal 25–30°C, but some can grow at refrigeration temperatures.
  • Ethanol Tolerance: Up to 18% alcohol.
  • Sugar Tolerance: Can grow in 55–60% sucrose.

Types of Food-Related Yeasts

• Beneficial Yeasts: Used in fermentation.
  • Saccharomyces cerevisiae: Baker’s and brewer’s yeast.
  • Candida utilis: Used in single-cell protein production.
  • Kluyveromyces lactis: Used in lactose fermentation for dairy products.

• Spoilage Yeasts: Cause fermentation and off-flavors.
  • Candida tropicalis: Common in fruit juices and dairy.
  • Debaryomyces hansenii: Found in cheese and salted foods.
  • Rhodotorula: Pink-colored yeast on butter, meat, and poultry.

• Control Methods

1. Pasteurization: Heat treatment destroys yeast cells.
2. Low pH: Acidic environments inhibit growth.
3. Reduced Water Activity: Yeasts are inhibited in dry foods.
4. Preservatives: Sorbates, benzoates, and sulfites prevent spoilage.

• Molds in Food Science

Molds are multicellular filamentous fungi that form mycelium, composed of hyphae. Molds can spoil food and produce harmful mycotoxins, but some are useful in fermentation.

• Characteristics
• Growth Form: Mycelial growth with branching hyphae.
• Color: Can be white, green, black, yellow, or blue.
• Reproduction: By spores (conidia, ascospores).
• Growth Conditions:
  • pH: Can grow at pH 2 to 8.5.
  • Temperature: Optimal 20–30°C, some tolerate refrigeration.
  • Moisture: Can grow at lower water activity (aw 0.7–0.8).

• Types of Food-Related Molds

1. Beneficial Molds: Penicillium roqueforti: Used in blue cheese production. Aspergillus oryzae: Used in soy sauce and sake fermentation.
2. Spoilage Molds: Rhizopus stolonifer: Bread mold. Mucor spp.: Spoils fruits, vegetables, and dairy. Geotrichum candidum: Found in dairy products (“dairy mold”).
3. Toxin-Producing Molds (Mycotoxins): Aspergillus flavus: Produces aflatoxins in grains, nuts, and spices. Penicillium spp.: Produces ochratoxin A in cereals and coffee. Fusarium spp.: Produces fumonisins and trichothecenes in grains.

• Control Methods

1. Temperature: Freezing and pasteurization inhibit mold growth.
2. Drying: Reducing moisture prevents mold growth.
3. Proper Storage: Store foods in airtight containers at cool temperatures.
4. Preservatives: Propionates, sorbates, and benzoates inhibit molds.

Comparison of Bacteria, Yeasts, and Molds