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?

Lactic acid bacteria Signup and view all the answers

What primarily influences the quality of the milk produced?

Farm environment and milking method Signup and view all the answers

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

They contain more harmful pathogens. Signup and view all the answers

What is the neutral pH level of milk?

6.7 Signup and view all the answers

Which type of microorganisms are considered spoilage organisms in milk?

Bacteria that produce lactic acid Signup and view all the answers

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

Using automatic milking methods. Signup and view all the answers

What types of microorganisms can be found in milk?

Both spoilage and pathogenic microorganisms Signup and view all the answers

What primarily indicates the presence of pathogens in milk?

Presence of coliforms Signup and view all the answers

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

Psychrotrophic organisms Signup and view all the answers

Which of the following microorganisms is known to survive pasteurization?

Pseudomonas fluorescens Signup and view all the answers

What temperature range is considered optimal for coliform growth?

Around 37°C Signup and view all the answers

Which pathogenic microorganism is associated with improperly handled dairy products?

Listeria monocytogenes Signup and view all the answers

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

Thermophilic Signup and view all the answers

What is the role of fast pasteurization in milk treatment?

Reduce pathogen presence Signup and view all the answers

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

E. coli Signup and view all the answers

What happens to acid-producing bacteria at low temperatures?

They become dormant Signup and view all the answers

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

All of the above Signup and view all the answers

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

4°C Signup and view all the answers

Which method effectively eliminates most spoilage microbes in milk?

Pasteurization Signup and view all the answers

What are the two types of pasteurization methods?

Slow and fast pasteurization Signup and view all the answers

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

61.1°C for 10 minutes Signup and view all the answers

What is the purpose of the phosphatase test in milk?

To indicate proper pasteurization Signup and view all the answers

At what temperature and duration does slow pasteurization occur?

62.85°C for 30 minutes Signup and view all the answers

Which bacteria can continue to grow even under cooling conditions?

Thermoduric bacteria Signup and view all the answers

What happens to the nutritional components of milk after pasteurization?

They mostly remain intact. Signup and view all the answers

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

It reduces the growth rate of microbes. Signup and view all the answers

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

It is a reliable indicator of product safety. Signup and view all the answers

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

Thermophilic bacteria Signup and view all the answers

What changes may result from thermoduric bacteria in milk?

Undesirable changes in flavor and quality Signup and view all the answers

What is the significance of coliform bacteria in pasteurized milk?

Their presence suggests potential contamination. Signup and view all the answers

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

Pseudomonas Signup and view all the answers

Which bacterial group is least likely to survive pasteurization?

Coliform group Signup and view all the answers

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

Psychrophilic bacteria Signup and view all the answers

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

Thermoduric bacteria Signup and view all the answers

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

They belong to the Bacillus and Clostridium genera. Signup and view all the answers

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

Spoilage under refrigeration Signup and view all the answers

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.