Lecture_4__Fermentation_cultures_

Fermentation Overview

  • Fermentations can be performed through different methods:

    • Spontaneous Fermentation: Encourages endogenous flora growth via initial raw material treatment.

    • Back Slopping: Involves using a portion of a previous batch to inoculate a new one (common in artisanal cheese).

    • Starter Culture: Added when raw materials are treated to inactivate endogenous flora (applied in yogurt and cheese).

Defined Starter Cultures

  • Using a defined mixture of starter cultures enhances consistency and flavor:

    • Single Strain Starter: A single strain known for its properties.

    • Multiple Strain Starter: 2 to 6 well-defined strains with known attributes.

    • Mixed Strain Starter: An undefined number of strains with no specific characteristics.

Bacterial Starter Cultures

  • Predominantly made of Lactic Acid Bacteria (LAB):

    • Ferment lactose to produce lactic acid, crucial for initiating fermentation.

    • Examples include:

      • Bifidobacterium spp.: Not classified as LAB but produce lactic acid, beneficial for flavor and probiotics.

      • Pediococci: Used in fermented meats.

      • Propionic Acid Bacteria: Essential in cheese ripening.

Characteristics of Lactic Acid Bacteria (LAB)

  • Generally:

    • Gram Positive: Can be rods or cocci.

    • Non-Sporforming and Microaerophilic: Thrive in reduced oxygen.

    • Acid Tolerant: Survive in low pH conditions (pH 3).

    • Fermentative: Convert carbohydrates into lactic acid (homofermentative).

    • Food Safety: Recognized as Generally Regarded As Safe (GRAS) by the FDA.

    • Probiotic Potential: Many LAB exhibit probiotic traits.

Hexose Fermentation Patterns in LAB

  • Two main pathways:

    • Heterofermentative: Produces lactic acid, CO2, acetic acid, and ethanol (via phosphoketolase pathway).

    • Homofermentative: Primarily yields lactic acid (via the Embden-Meyerhof pathway).

    • Some strains exhibit facultative heterofermentation capabilities.

Problems in Dairy Fermentations

  • Cell Death & Injury: Caused by freeze-thaw cycles or freeze-drying and rehydration.

  • Loss of Desired Trait: Strains can lose important traits during storage or sub-culturing.

  • Strain Antagonism: Competition between strains in mixed cultures can alter profiles.

  • Inhibitors in Raw Materials: Milk can contain antibiotics or sanitizers that affect cultures.

Bacteriophages in Fermentation

  • Impact of Bacteriophages:

    • Can cause starter culture failure by rapidly spreading in fermentation vats, leading to reduced acidification and spoilage.

    • Bacteriophages are viruses that target bacteria, often surviving pasteurization and requiring rigorous heat treatment.

Control Methods for Phage Attack

  • Preventative Measures:

    • Purchase freeze-dried starter cultures from reliable suppliers.

    • Ensure sanitation to minimize phage build-up.

    • Use phage inhibitory media and rotate strains to prevent specific phage dominance.

    • Incorporate mixed strains to mitigate phage accumulation effects.

Probiotics

  • Defined as “live microbes conferring health benefits above basic nutrition” (FAO/WHO).

  • Many LAB, such as Lactobacilli and Streptococcus, possess probiotic traits.

  • Commonly consumed through fermented dairy products (e.g., yogurt).

  • Non-LAB Probiotics: Include Bacillus sp. and Saccharomyces cerevisiae.

Key Properties of Probiotics

  1. Nonpathogenic: Should not cause harm or produce toxins.

  2. Digestive Survival: Must survive intestinal passage.

  3. Adherence: Should attach and colonize the gastrointestinal tract.

  4. Nutrient Utilization: Capable of accessing nutrients in typical diets.

  5. Viability: Must remain alive in the form consumed.

  6. Beneficial Effects: Should confer health benefits, such as enhancing immunity or preventing infections.

Probiotics and Functional Foods

  • Characteristics:

    • Must outlive expiration date (> 106 CFU/g or /ml).

    • Benefits beyond GI health, like reducing cholesterol and modulating the immune system.

    • Nutraceuticals: Foods offering health benefits beyond basic nutrition.

Bacterial Flora Overview

  • Good Bacteria:

    • Bifidobacteria: Regulate gut flora, enhance immunity, prevent tumors.

    • Lactobacilli: Contribute to vitamin production and immune defense.

  • Bad Bacteria:

    • Campylobacter: Causes foodborne illness.

    • Clostridium difficile: Can proliferate post-antibiotic use leading to infections.

Yeast Starter Cultures**

  • Role in Fermentation: Used in both spontaneous and controlled fermentations.

  • Yeasts convert carbohydrates into alcohols and CO2, enhancing aroma production.

  • Example: Saccharomyces cerevisiae is the main yeast used in bread, wine, beer, and cheese.

Mould Starter Cultures

  • Employed for cheese and fermented meat production, particularly in Europe.

  • Function under aerobic conditions, effective in enzyme and aroma compound production.

  • Examples include:

    • Penicillium roqueforti: Used for Roquefort cheese.

    • Penicillium camemberti: Associated with Camembert cheese.

Future of Microbiome in Dietary Recommendations

  • The impact of fermented foods on gut health and potential inclusion in dietary guidelines is being explored.