Dairy Science Quiz
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Questions and Answers

What is the primary composition of milk by percentage?

  • 85% water, 15% solids
  • 90% water, 10% solids
  • 87.4% water, 12.6% solids (correct)
  • 76.5% water, 23.5% solids

Which component is NOT found in milk?

  • Glucose (correct)
  • Lactose
  • Fat
  • Proteins

How does milk become contaminated?

  • It is sterile until consumed.
  • Contamination is only due to poor storage.
  • Contamination starts after milking. (correct)
  • Contamination occurs only in cases of mastitis.

Which bacteria group ferments lactose to lactic acid?

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

What primarily influences the quality of the milk produced?

<p>Farm environment and milking method (B)</p> Signup and view all the answers

What is the main reason to exclude the first quantities from the milking process?

<p>They contain more harmful pathogens. (C)</p> Signup and view all the answers

What is the neutral pH level of milk?

<p>6.7 (A)</p> Signup and view all the answers

Which type of microorganisms are considered spoilage organisms in milk?

<p>Bacteria that produce lactic acid (D)</p> Signup and view all the answers

Which of the following is a method to prevent milk contamination?

<p>Using automatic milking methods. (D)</p> Signup and view all the answers

What types of microorganisms can be found in milk?

<p>Both spoilage and pathogenic microorganisms (D)</p> Signup and view all the answers

What primarily indicates the presence of pathogens in milk?

<p>Presence of coliforms (C)</p> Signup and view all the answers

Which type of microorganisms is mainly responsible for spoilage in milk at low temperatures?

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

Which of the following microorganisms is known to survive pasteurization?

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

What temperature range is considered optimal for coliform growth?

<p>Around 37°C (B)</p> Signup and view all the answers

Which pathogenic microorganism is associated with improperly handled dairy products?

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

Which type of bacteria can grow at temperatures above 65°C?

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

What is the role of fast pasteurization in milk treatment?

<p>Reduce pathogen presence (B)</p> Signup and view all the answers

Which of the following is NOT a common spoilage organism in milk?

<p>E. coli (A)</p> Signup and view all the answers

What happens to acid-producing bacteria at low temperatures?

<p>They become dormant (B)</p> Signup and view all the answers

Which bacterial pathogen is specifically linked to milk-borne illnesses?

<p>All of the above (D)</p> Signup and view all the answers

What temperature is ideal for cooling milk to maintain its quality?

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

Which method effectively eliminates most spoilage microbes in milk?

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

What are the two types of pasteurization methods?

<p>Slow and fast pasteurization (C)</p> Signup and view all the answers

What temperature is required for the heat-resistant Mycobacterium tuberculosis to be eliminated in milk?

<p>61.1°C for 10 minutes (B)</p> Signup and view all the answers

What is the purpose of the phosphatase test in milk?

<p>To indicate proper pasteurization (C)</p> Signup and view all the answers

At what temperature and duration does slow pasteurization occur?

<p>62.85°C for 30 minutes (D)</p> Signup and view all the answers

Which bacteria can continue to grow even under cooling conditions?

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

What happens to the nutritional components of milk after pasteurization?

<p>They mostly remain intact. (C)</p> Signup and view all the answers

What is the main effect of cooling milk immediately after milking?

<p>It reduces the growth rate of microbes. (A)</p> Signup and view all the answers

What does the heat stability of ALP indicate about a milk product?

<p>It is a reliable indicator of product safety. (A), It suggests the product may contain heat-resistant bacteria. (C)</p> Signup and view all the answers

Which type of bacteria can survive the pasteurization process and potentially spoil milk?

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

What changes may result from thermoduric bacteria in milk?

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

What is the significance of coliform bacteria in pasteurized milk?

<p>Their presence suggests potential contamination. (C)</p> Signup and view all the answers

Which of the following bacteria are associated with producing fruity or rancid tastes in milk?

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

Which bacterial group is least likely to survive pasteurization?

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

Which of these bacteria is primarily known for causing spoilage during refrigerated storage?

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

What type of bacteria typically utilizes milk components as a nutrient source and can endure heat treatment?

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

Which of the following is true about spore-forming bacteria in pasteurized milk?

<p>They belong to the Bacillus and Clostridium genera. (A)</p> Signup and view all the answers

What is a potential defect from the presence of thermophilic bacteria in milk?

<p>Spoilage under refrigeration (A)</p> Signup and view all the answers

Flashcards

Milk Contamination

Milk, a nutrient-rich liquid, is naturally sterile when secreted from the udder but is contaminated by bacteria even before leaving the udder. However, these bacteria are usually harmless and few in number unless mastitis occurs.

Milk Composition

The main components of milk are water (87.4%) and solids (12.6%). Solids include lactose, protein (like casein and albumin), fat, minerals, and vitamins.

Factors Influencing Milk Contamination

The number and type of microbes in milk vary depending on factors like the animal's health, milking methods, farm environment, transportation, storage, and processing.

Discarding the First Milk

The first quantity of milk drawn from the udder should be discarded as it is likely to contain higher levels of bacteria.

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Milk Spoilage

Spoilage bacteria in milk cause changes that give it an undesirable taste, smell, or appearance, and can result in the milk becoming unsafe to consume.

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Lactic Acid Bacteria

Lactic acid bacteria are a type of bacteria that ferment lactose in milk, resulting in the production of lactic acid. This process is utilized in the production of various fermented dairy products.

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Pathogenic Bacteria in Milk

Pathogenic bacteria present in milk can cause illness or disease. They can be either infectious, spreading through consumption of the milk, or toxin-producing, where the bacteria release harmful toxins into the milk.

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Lactic Acid Bacteria in Dairy Products

Lactic acid bacteria are a type of spoilage bacteria involved in the fermentation process, but they are also used in the production of fermented dairy products like yogurt.

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Milk's pH

Milk is generally considered to be neutral in acidity, with a pH of around 6.7.

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Mastitis

Mastitis is an infection of the udder in cows, leading to higher levels of bacteria in the milk. It can be caused by various bacterial species, including Staphylococcus aureus and Streptococcus agalactiae.

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Lactococci

Bacteria found in milk that produce lactic acid, often used in cheese and yogurt production.

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Psychrotrophic Organisms

A type of bacteria that thrives in cool temperatures, often responsible for spoilage in refrigerated milk.

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Facultative Anaerobes

Bacteria that can survive and grow in the presence or absence of oxygen.

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Coliforms

A group of bacteria that are commonly found in the intestines of warm-blooded animals, often used as indicators of fecal contamination.

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Heat-Resistant Bacteria

Bacteria that are heat-resistant and can survive pasteurization, potentially causing spoilage.

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Pasteurization

The process of heating milk to a specific temperature for a set time to kill harmful bacteria.

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Brucellosis

A bacterial infection that can be transmitted through contaminated milk, causing fever, chills, and muscle aches.

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Tuberculosis

A bacterial infection that can be transmitted through contaminated milk, causing a persistent cough and chest pain.

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Typhoid Fever

A bacterial infection that can be transmitted through contaminated milk, causing fever, headache, and abdominal pain.

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Campylobacteriosis

A bacterial infection that can be transmitted through contaminated milk, causing diarrhea and cramps.

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What is Pasteurization?

The process of preserving milk by heating it to a specific temperature which results in the elimination of most harmful bacteria. This process ensures the safety and extends the shelf life of milk.

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Alkaline Phosphatase (ALP)

This enzyme acts as a safety indicator in milk because it is more heat-resistant than potential pathogens.

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What is Slow Pasteurization (Low Temperature Holding Method - LTHM)?

A method of pasteurization where milk is heated to 62.85°C for 30 minutes. This process ensures effective destruction of most bacteria, including pathogens, without significantly affecting the milk's taste or nutritional value.

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Thermoduric Bacteria

Bacteria that survive even after pasteurization.

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What is Fast Pasteurization (High Temperature Short Time - HTST)?

Another method of pasteurization where milk is heated to 71.75°C for 15 seconds. This method is quicker than slow pasteurization but is equally effective in eliminating unwanted bacteria.

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Psychrophilic Bacteria

These bacteria thrive even in cold temperatures and cause spoilage in milk.

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What is Alkaline Phosphatase (ALP)?

This enzyme is naturally present in raw milk and acts as an indicator of proper pasteurization. The enzyme is inactivated during pasteurization indicating that the milk is safe to consume.

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What is the importance of cooling milk?

The rate at which microbes grow in milk is reduced considerably when the milk is cooled to 4°C. This method helps to preserve the quality of the milk and extend its shelf life.

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Coliform Group

Bacteria that cannot survive pasteurization, their presence indicates contamination.

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False Negative ALP Test

Milk can still be safe even if the ALP test is negative, as some pathogens might be resistant to the heat.

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What are Thermoduric Bacteria?

Bacteria that thrive in higher temperatures and are resistant to conventional pasteurization methods. They can survive even in cooled milk, but their growth rate is significantly slowed down.

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What are Examples of Thermoduric Bacteria?

This type of bacteria thrives in temperatures between 20°C and 65°C. Cooling milk effectively restricts their growth but does not eliminate them entirely.

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Thermophilic Bacteria

Bacteria thriving at high temperatures, they survive pasteurization.

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Thermoduric Bacteria

These bacteria cause undesirable changes in milk flavor and quality over time, even if they don't survive pasteurization.

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What is a Minimum Growth Temperature of Bacteria?

The lowest temperature at which a particular bacterial type can survive and grow. Psychrotrophic bacteria have a lower minimum temperature requirement (7°C) compared to mesophilic bacteria (20°C).

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What are Psychrotrophic Bacteria?

Bacteria that thrive at low temperatures, around 7°C. They are often found in milk and can cause spoilage even during refrigerated storage.

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Classic Phosphatase Test

The classic test for ALP activity involves reacting with a substrate, causing a color change.

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What are Mesophilic Bacteria?

Bacteria that thrive at moderate temperatures, ranging from 20°C to 45°C. They are a major concern during milk storage and processing as they can contribute to spoilage.

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Rapid Phosphatase Test

This test for ALP activity provides faster results compared to the traditional method, using different techniques.

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Spore-forming Bacteria

These bacteria can survive pasturization but can still cause spoilage, their presence indicates the pasteurization process wasn't efficient.

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Study Notes

Applied Dairy Microbiology

  • Dairy microbiology is a subfield of applied microbiology focusing on microorganisms in milk.

Milk Composition

  • Milk is a nutrient-rich liquid secreted by glands.
  • Major components are water (87.4%) and solids (12.6%).
  • Solids include lactose (5%), protein (3%), fat (3.5%), minerals (1%), and vitamins (A, E, K, B, C).
  • Milk contains enzymes like catalase, lipase, and phosphatase.
  • Milk is neutral, with a pH of approximately 6.7.

Milk Contamination Sources

  • Milk is sterile at secretion but can become contaminated before leaving the udder, even in the absence of mastitis.
  • Initial contamination is typically harmless and low in number.
  • First milk should be excluded from the milking process.
  • Post-milking contamination sources include the milking process, tools, air, animal skin and udder, animal sheds, milking staff, and water supplies.
  • The quality of milk depends on production conditions and microbial load.

Microorganisms in Milk

  • Spoilage microorganisms are categorized into four groups based on the physiological process. These groups produce: lactic acid, propionic acid, butyric acid, and degradative enzymes.
  • Certain spoilage organisms, like lactic acid bacteria, can be used to create fermented dairy products under controlled conditions.
  • Pathogenic microorganisms in milk can be infectious or toxin-producing.

Types of Bacteria in Milk

  • (1) Lactic Acid Bacteria*

  • Ferment lactose to lactic acid.

  • Commonly used as starters in yogurt production.

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

  • (2) Coliforms*

  • Facultative anaerobes; optimal growth at 37°C.

  • Indicator organisms; often linked to pathogens, but not always pathogenic themselves.

  • Cause rapid milk spoilage by fermenting lactose and degrading proteins.

  • Killed by pasteurization.

  • (3) Spoilage Microorganisms*

  • Psychrotrophic organisms are predominantly involved in milk spoilage.

  • Pseudomonas fluorescens and Pseudomonas fragi are examples, which produce proteolytic and lipolytic enzymes.

  • These enzymes are heat-stable and cause spoilage.

  • Some species, like Bacillus, Clostridium, and others, can grow in refrigerators.

  • (4) Pathogenic Microorganisms*

  • Hygienic practices, proper handling and storage, and mandatory pasteurization reduce the threat of milkborne diseases.

  • Raw milk and improperly pasteurized milk products can still present a risk.

  • Examples: Bacillus cereus, Listeria monocytogenes, Yersinia sp., Salmonella, E. coli O157:H7, and Campylobacter jejuni.

Effect of Temperature on Milk Microbes

  • Psychrophilic: thrive at near zero degrees Celsius.
  • Mesophilic: thrive at room temperature.
  • Thermophilic: thrive above 65°C.
  • Heat-resistant microbes live after pasteurisation.
  • Low temperatures inhibit acid-producing bacteria and increase protein-degrading bacteria activity.
  • Moderate temperatures boost acid-producing and slow down protein and fat-degrading bacteria.
  • High temperatures kill acid-producing bacteria, and some bacterial spores remain to degrade proteins when milk is boiled.

Milk Preservation Methods

  • Milk is cooled to around 4°C after milking to maintain quality and extend shelf life.
  • Cooling reduces microbial growth, especially mesophilic and psychrotrophic bacteria.
  • Constant cooling during transportation and handling is critical.
  • Cooling reduces thermoduric bacteria (like Bacillus cereus) activity.
  • Cooling also does not completely eliminate them, which can grow though even at slow rate

Pasteurization

  • Mild heat treatment that eliminates most spoilage and pathogenic microbes.
  • Mycobacterium tuberculosis, a heat-resistant pathogenic microbe, is inactivated at 61.1°C for 10 minutes.
  • Preserve nutritional components like vitamins and calcium.
  • Not substantially alter taste or appearance.

Types of Pasteurization

  • Low Temperature Holding Method (LTHM): 62.85°C for 30 minutes.
  • High Temperature Short Time Method (HTST): 71.75°C for 15 seconds.

Phosphatase Test

  • Alkaline phosphatase (ALP) is an enzyme present in raw milk.
  • Absence of ALP in milk indicates proper pasteurization.
  • There are classic and rapid tests to detect ALP for milk pasteurization effectiveness assurance.

Microbes in Pasteurized Milk

  • Thermophilic bacteria can survive pasteurization and proliferate in improperly stored pasteurized milk. Examples: Streptococcus thermophilus and Lactobacillus delbrueckii
  • Thermoduric bacteria can endure the heat treatment and influence milk flavor and quality over time. Examples: Streptococcus spp., Enterococcus spp., and Lactobacillus spp..
  • Psychrophilic bacteria cause defects like fruitiness, rancidity, or acidity in pasteurized milk.. Examples: Alcaligenes, Pseudomonas, and Lactococcus
  • Spore-forming bacteria (Bacillus and Clostridium): can survive pasteurization and cause spoilage at times.
  • Coliform bacteria can withstand pasteurization but not significantly impact taste or appearance.

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Description

Test your knowledge on the composition and microbiology of milk with this quiz. Explore topics such as contamination, spoilage organisms, and the fermentation process. Ideal for students and dairy science enthusiasts looking to enhance their understanding of milk quality and safety.

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