Dairy Microbiology Overview
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Questions and Answers

What is the primary component of milk by percentage?

  • Lactose (5%)
  • Solids (12.6%)
  • Fat (3.5%)
  • Water (87.4%) (correct)

Which of the following microorganisms is commonly responsible for spoilage in milk?

  • Listeria monocytogenes
  • Lactic acid bacteria (correct)
  • Staphylococcus aureus
  • E. coli

What is the pH level typical for milk?

  • 7.5
  • 6.7 (correct)
  • 5.5
  • 8.0

Which factor does NOT affect the quality of milk production?

<p>Time of day milked (D)</p> Signup and view all the answers

What is the role of lactic acid bacteria in dairy production?

<p>They ferment lactose to lactic acid. (D)</p> Signup and view all the answers

What type of microorganisms are considered pathogenic in milk?

<p>Infectious or toxin-producing bacteria (A)</p> Signup and view all the answers

Which of the following is NOT a component of milk solids?

<p>Water (A)</p> Signup and view all the answers

Which of the following is a method for reducing microbial contamination in milk?

<p>Using sterilized equipment (D)</p> Signup and view all the answers

What is the main reason for recommending the exclusion of first quantities from the milking process?

<p>They often contain higher levels of bacteria (A)</p> Signup and view all the answers

Which vitamin is NOT commonly found in milk?

<p>Vitamin D (B)</p> Signup and view all the answers

What type of microorganisms are coliforms known to be?

<p>Facultative anaerobes (A)</p> Signup and view all the answers

Which spoilage microorganism is capable of producing heat-stable enzymes?

<p>Pseudomonas fluorescens (C)</p> Signup and view all the answers

Which temperature classification best describes microorganisms that can grow near zero degrees Celsius?

<p>Psychrophilic (A)</p> Signup and view all the answers

What happens to the activity of acid-producing bacteria at low temperatures?

<p>It completely stops (D)</p> Signup and view all the answers

Which of the following pathogens is NOT commonly associated with raw milk?

<p>Bacillus subtilis (C)</p> Signup and view all the answers

What is an important characteristic of coliforms related to milk spoilage?

<p>They can ferment lactose producing acid and gas (B)</p> Signup and view all the answers

Which organism is primarily responsible for spoilage in refrigerated milk?

<p>Clostridium (B)</p> Signup and view all the answers

What is the effect of fast pasteurization on coliforms?

<p>It kills them (A)</p> Signup and view all the answers

Which organism is considered an indicator of milk contamination?

<p>Escherichia coli (B)</p> Signup and view all the answers

What role do hygienic milk production practices play?

<p>They decrease the threat of milk-borne diseases. (D)</p> Signup and view all the answers

What does the presence of ALP in milk indicate?

<p>Product safety (C)</p> Signup and view all the answers

Which type of bacteria can survive the pasteurization process and potentially cause spoilage?

<p>Thermophilic bacteria (D)</p> Signup and view all the answers

What is a potential outcome of thermoduric bacteria in milk?

<p>Undesirable changes in flavor (D)</p> Signup and view all the answers

Which bacteria group is known to cause defects such as fruity or rancid tastes in milk after pasteurization?

<p>Psychrophilic bacteria (B)</p> Signup and view all the answers

What does the presence of coliform bacteria in pasteurized milk suggest?

<p>Inefficiency in the pasteurization process (B)</p> Signup and view all the answers

Which of the following types of bacteria is particularly resilient due to its ability to form spores?

<p>Spore-forming bacteria (C)</p> Signup and view all the answers

What may happen if milk is stored improperly after pasteurization?

<p>Proliferation of thermophilic bacteria (A)</p> Signup and view all the answers

Which bacteria are known for utilizing milk components and may lead to flavor changes?

<p>Thermoduric bacteria (A)</p> Signup and view all the answers

Which of these bacteria types typically does not thrive in the pasteurization heat?

<p>Coliform group (A)</p> Signup and view all the answers

What is a common consequence of bacterial activity after pasteurization?

<p>Flavor and quality defects (A)</p> Signup and view all the answers

What temperature is typically maintained to enhance milk quality and shelf life immediately after milking?

<p>4°C (C)</p> Signup and view all the answers

What is a consequence of boiling milk regarding acid-producing bacteria?

<p>They die, allowing other bacteria to dominate. (C)</p> Signup and view all the answers

Which of the following bacteria is known to cause tuberculosis and is targeted during pasteurization?

<p>Mycobacterium tuberculosis (A)</p> Signup and view all the answers

Which pasteurization method involves treating milk at 62.85°C for 30 minutes?

<p>Slow Temperature Holding Method (LTHM) (B)</p> Signup and view all the answers

What effect does cooling milk have on thermoduric bacteria?

<p>It reduces their activity but does not eliminate them. (C)</p> Signup and view all the answers

What is the maximum temperature needed to inactivate Mycobacterium tuberculosis during pasteurization?

<p>61.1°C (B)</p> Signup and view all the answers

What is the purpose of the phosphatase test in milk processing?

<p>To indicate adequate pasteurization. (D)</p> Signup and view all the answers

What is primarily preserved when milk undergoes pasteurization?

<p>Vitamins, calcium, and nutritional components (C)</p> Signup and view all the answers

At what temperature is milk typically treated using the High Temperature Short Time method?

<p>71.75°C for 15 seconds (D)</p> Signup and view all the answers

What happens to the bacterial spores remaining in milk after boiling?

<p>They remain viable and can degrade proteins. (A)</p> Signup and view all the answers

Flashcards

Lactic Acid Fermentation

The process of bacteria converting lactose into lactic acid, producing a sour taste and changing milk's texture.

Lactic Acid Bacteria

A type of bacteria that produces lactic acid during fermentation, often used to create yogurt and cheese.

Spoilage Microorganisms

Microorganisms that cause spoilage in milk, altering its taste, smell, and appearance.

Milk Contaminants

Bacteria, yeasts and fungi that can contaminate milk from the time it's milked until consumption.

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Animal Health

The condition of the udder in a lactating animal, impacting the contamination level of milk.

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Milking Method

The method of milking, whether by hand or machine, affects the extent of bacterial contamination.

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Farm Environment

The environment where the animal lives and is milked influences the types of microbes that can contaminate the milk.

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Transportation

The process of transporting milk from the farm to processing facilities can introduce contaminants.

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Pre-processing Activities

Milk can become contaminated after milking, during processing, and storage if appropriate hygiene is not followed.

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Milk Quality

The overall quality of milk, largely dependent on the level of contamination and the conditions of its production.

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Thermophilic bacteria

These bacteria survive pasteurization but can multiply in refrigerated milk, causing spoilage.

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Thermoduric bacteria

These bacteria can withstand pasteurization but don't multiply as quickly as thermophilic bacteria. They can still alter milk's flavor and quality over time.

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Psychrophilic bacteria

These bacteria prefer cold temperatures and cause defects like fruity or acidic tastes in milk that appears days later.

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Spore-forming bacteria

These bacteria, like Bacillus and Clostridium, form spores that can survive pasteurization. They can cause spoilage and even potentially harmful toxins.

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Coliform bacteria

These bacteria are a type of indicator organism. Their presence in pasteurized milk suggests contamination or improper pasteurization, but they don't have a significant impact on milk quality.

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Alkaline Phosphatase (ALP)

ALP activity serves as an indicator of proper pasteurization and product safety.

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Pasteurization

This process uses heat to kill harmful bacteria in milk, making it safe for consumption.

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Ultra-High Temperature (UHT) Processing

The process of heating milk to very high temperatures for a short period of time to instantly kill bacteria.

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Post-pasteurization contamination

The presence of these bacteria suggests that the pasteurization process was ineffective or that the milk was contaminated after pasteurization.

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Milk spoilage

This refers to the growth of microorganisms in milk, resulting in changes in taste, smell, and appearance.

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Slow Pasteurization (LTHM)

A type of pasteurization using lower temperatures for longer durations, ensuring the destruction of pathogens.

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Fast Pasteurization (HTST)

A type of pasteurization using higher temperatures for shorter durations, also effective in eliminating pathogens.

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Milk Cooling Temperature

The temperature at which milk is cooled to slow down bacterial growth and maintain quality.

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Psychrotrophic Bacteria

Bacteria that thrive at low temperatures and can still grow in refrigerated milk.

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Mycobacterium tuberculosis

The causative agent of tuberculosis, a heat-resistant bacterium that is effectively eliminated by proper pasteurization.

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Thermal Death Point (TDP)

A measurement of the time and temperature required to eliminate bacteria, ensuring proper pasteurization.

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Coliforms

Bacteria that ferment lactose, producing acid and gas, contributing to milk spoilage.

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Lactococci

A group of bacteria that are commonly found in milk and are known for their ability to ferment lactose, producing lactic acid.

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Psychrotrophic organisms

Bacteria that can grow at low temperatures, causing spoilage of milk even in the refrigerator.

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Heat-resistant bacteria

A type of bacteria that can survive even after the pasteurization process, potentially causing spoilage due to their heat resistance.

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Lactobacillus casei

A bacterium responsible for the souring of milk by producing lactic acid.

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Mesophilic organisms

A type of bacteria that thrives in warm temperatures, causing spoilage problems at room temperature.

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Thermophilic organisms

A type of bacteria that prefers extremely high temperatures, capable of growing at temperatures above 65°C.

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Listeria monocytogenes

A bacterium commonly found in raw milk that can cause foodborne illnesses.

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Salmonella spp.

A type of bacteria that can cause foodborne illnesses, often associated with raw milk and dairy products.

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Escherichia coli O157:H7

A bacterium that can cause foodborne illnesses, often found in raw milk and other dairy products.

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Study Notes

Dairy Microbiology

  • Dairy microbiology is a branch of applied microbiology focusing on dairy products.

Milk Composition

  • Milk is a nutrient-rich liquid secreted by glands.
  • Major components:
    • Water (87.4%)
    • Solids (12.6%):
      • Lactose (5%)
      • Protein (3%, e.g., casein, albumin)
      • Fat (3.5%)
      • Minerals (1%, e.g., calcium)
      • Vitamins (A, E, K, B, C)
      • Enzymes (e.g., catalase, lipase, phosphatase)
  • Milk is neutral, with a pH of about 6.7.

Sources of Milk Contamination

  • Milk is sterile at secretion but can be contaminated:
    • Before leaving the udder (except in mastitis cases, where bacteria are harmless and few).
    • During milking and handling
    • Throughout the processing and storage.
  • Contamination sources include:
    • Animal health
    • Milking method (manual or automatic)
    • Farm environment
    • Transportation
    • Storage conditions
    • Pre-processing activities

Milk Contamination Sources

  • Air
  • Animal skin
  • Milking staff
  • Tools and supplies
  • Udder (interior and exterior)
  • Animal shed

Microorganisms in Milk

  • Important microorganisms: spoilage and pathogenic.
  • Spoilage organisms belong to 4 physiological groups producing:
    • Lactic acid, propionic acid, butyric acid, degradative enzymes
  • Some spoilage organisms (e.g., lactic acid bacteria) can be used to produce dairy foods under controlled conditions.
  • Pathogenic microorganisms can be infectious or toxin-producing.

Types of Bacteria in Milk

  • (1) Lactic Acid Bacteria*

  • Ferment lactose to lactic acid.

  • Used as starters for various dairy products (e.g., yogurt).

  • Examples: Lactococci (e.g., Lactococcus lactis), Lactobacilli (e.g., Lactobacillus casei), Leuconostoc (e.g., Leuconostoc lactis)

  • (2) Coliforms*

  • Facultative anaerobes, optimal growth at 37°C.

  • Indicator organisms for pathogens.

  • Spoilage microorganisms causing acid and gas production and degradation of milk proteins.

  • Killed by pasteurization.

  • Example: Escherichia coli.

  • (3) Spoilage Microorganisms in Milk*

  • Primarily psychrotrophic (can grow at low temperatures).

  • Many are destroyed by pasteurization but some (e.g., Pseudomonas fluorescens, Pseudomonas fragi) produce heat-stable enzymes causing spoilage.

  • Examples: Bacillus, Clostridium, Cornebacterium, Lactobacillus, Micrococcus, Streptococcus.

  • (4) Pathogenic Microorganisms in Milk*

  • Milk-borne diseases (e.g., tuberculosis, brucellosis, typhoid fever) have been reduced due to improved hygienic practices, pasteurization and milk handling.

  • Raw milk and some dairy products can still be sources of pathogenic bacteria (e.g., Bacillus cereus, Listeria monocytogenes, Yersinia sp., Salmonella spp., Escherichia coli O157:H7, Campylobacter jejuni).

Effect of Temperature on Milk Microbes

  • Microbes have different temperature needs.
    • Psychrophilic (grow at low temperatures)
    • Mesophilic (grow at room temperature)
    • Thermophilic (grow at high temperatures)
    • Heat-resistant (survive pasteurization)
  • Low temperature: Acid-producing bacteria inactive, protein-degrading bacteria active.
  • Medium temperature: Acid-producing bacteria active, protein-degrading bacteria reduced.
  • High temperature (boiling): Acid-producing bacteria die, bacterial spores remain.

Methods of Preserving Milk

  • Cooling (e.g., 4°C) reduces microbial growth (especially mesophilic and psychrotrophic bacteria).
  • Constant temperature helps prevent activity by thermoduric bacteria (e.g., Bacillus cereus and Bacillus circulans).

Pasteurization

  • Mild heat treatment (90-99% bacteria killed).
  • Eliminates most spoilage and pathogenic microbes, including Mycobacterium tuberculosis.
  • Preserves nutritional components (e.g., vitamins and calcium), with minimal changes in taste and appearance.
  • Two types:
    • Slow Pasteurization (LTHM): 62.85°C for 30 minutes.
    • Fast Pasteurization (HTST): 71.75°C for 15 seconds.

Phosphatase Test

  • Alkaline phosphatase (ALP) is an enzyme present in raw milk.
  • ALP is inactivated by complete pasteurization.
  • Absence of ALP activity indicates proper pasteurization, it doesn't ensure pathogen-free milk.
  • Classic and rapid testing methods available.

Microbes in Milk After Pasteurization

  • Thermophilic bacteria: May survive and proliferate in refrigerated pasteurized milk, causing spoilage (e.g., Streptococcus thermophilus, Lactobacillus delbrueckii).

  • Thermoduric bacteria: Endure heat treatment (e.g., Streptococcus spp., Enterococcus spp., Lactobacillus spp) causing flavor and quality changes.

  • Psychrophilic bacteria: Spoilage defects appear after several days (eg. Alcaligenes, Pseudomonas, Lactococcus)

  • Spore-forming bacteria: Can survive pasteurization, and cause spoilage defects (e.g., Bacillus, Clostridium).

  • Coliform bacteria: Can survive pasteurization but have no significant effect.

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Explore the fascinating world of dairy microbiology, focusing on milk composition, sources of contamination, and the importance of proper handling and processing. This quiz will test your understanding of the key concepts related to dairy products and their microbiological aspects.

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