Dairy micro 12082024

Food 90012: Current Issues in Dairy Science

Faculty of Science - The University of Melbourne

  • Course focuses on dairy microbiology under the instruction of AProf Said Ajlouni.

Microbial Growth in Milk

Microorganisms in Milk

  • Milk is an ideal medium for the growth of:

    • Bacteria

    • Yeast

    • Mould

Pasteurisation

  • Purpose: Eliminate pathogenic microorganisms and reduce total bacteria count in milk.

Chemical Composition of Milk

Source

% Composition (Protein)

Casein

Whey Protein

Fat

Sugars

Cow

3.5%

2.8%

0.7%

3.7%

4.8%

Buffalo

4.0%

3.5%

0.5%

7.5%

4.8%

Goat

3.6%

2.7%

0.9%

4.1%

4.7%

Sheep

5.8%

4.9%

0.9%

7.9%

4.5%

Major Pathogens in Raw Milk

  • Pathogenic microorganisms include:

    • Bacillus cereus

    • Campylobacter jejuni

    • Echerichia coli

    • Listeria monocytogenes

    • Salmonella spp.

    • Yersinia enterocolitica

Major Spoilage Microorganisms

  • Spoilage Microbes include:

    • Pseudomonas fluorescens

    • Pseudomonas fragi

  • Produce heat-resistant extracellular proteolytic and lipolytic enzymes.

Spoilage Microbes That Survive Pasteurization

  • Species from Bacillus, Clostridium, Corynebacterium, Arthrobacter, Lactobacillus, Microbacterium, Micrococcus, and Streptococcus can survive the pasteurization process.

Desirable Microorganisms in Dairy Products

  • Starter cultures for fermentation.

  • Ripening organisms contribute to flavor development.

  • Probiotic organisms enhance gut health.

Lactic Acid Bacteria in Milk

  • Common types of lactic acid bacteria include:

    • Lactococcus lactis subsp. lactis (formerly Streptococcus lactis)

    • Lactococcus lactis subsp. cremoris (formerly Streptococcus cremoris)

    • Lactobacillus casei

    • L. delbrueckii subsp. lactis

    • L. delbrueckii subsp. bulgaricus (formerly Lactobacillus bulgaricus)

Indicator Microorganisms

  • Non-pathogenic microorganisms indicating potential pathogens, abuse, or contamination.

  • Coliforms serve as an example of indicator microorganisms.

Sources of Milk Contamination

  • **Direct Sources: **

    • Faeces: E. coli and other pathogens.

    • Infection in udders: Includes clinical and sub-clinical mastitis pathogens like Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, Staphylococcus aureus.

  • Environmental Sources:

    • Water containing Pseudomonas, dust from the environment containing Bacillus.

Milk-Borne Diseases

  • Diseases linked with contaminated milk include:

    • Typhoid Fever

    • Diphtheria

    • Scarlet Fever

    • Dysentery

    • Septic Sour Throat

Recent Dairy Product Recalls

  • Examples of recent recalls due to microbial contamination include:

    • Paris Creek Farms: Contaminated fresh butter (Yersinia enterocolitica).

    • Driftwood Cheese: E. Coli contamination.

    • Various Jalna products: Potential E. coli contamination.

    • Gippsland Jersey: Listeria monocytogenes contamination in milk.

Dairy Food Regulation in Australia

  • Governing body: Food Standard Australia New Zealand.

  • Refer to alerts for food recalls from 2023-2024 for compliance updates.

Microbiological Limits for Dairy Products

  • Regulations outline acceptable microbial counts in dairy products to ensure safety and quality, including counts for Campylobacter, coliforms, E. coli, and Salmonella.

Microbiology of Major Processed Dairy Products

  • Common products include:

    • Pasteurised Milk

    • UHT Milk

    • Butter

    • Milk Powder

    • Cheeses

    • Yoghurt

    • Ice Cream

Spoilage Factors in Dairy Products

  • Various factors contribute to spoilage, including contaminated raw materials, improper processing conditions, and microbial persistence through refrigeration.

Functional Foods

  • Functional foods, including probiotics, have specific health attributes beneficial especially for vulnerable populations like infants and the elderly.

Probiotics, Prebiotics, and Synbiotics

  • Probiotics: Live organisms promoting gut health.

    • Example: Lactobacillus acidophilus.

  • Prebiotics: Nutrients that nourish probiotics, such as inulin.

  • Synbiotics: Combination of probiotics and prebiotics working together for improved health benefits.

Somatic Cell Counts (SCC) in Milk Quality

  • SCC: Indicator of udder health; higher counts indicate infective conditions leading to decreased milk quality.

  • Infection thresholds:

    • <100,000 cells/ml = Uninfected cows.

    • 250,000 cells/ml = Infected cows.