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Questions and Answers
Pasteurization involves heating milk at 62°C for 30 minutes.
Pasteurization involves heating milk at 62°C for 30 minutes.
True
Sterilization involves heating milk at 71.6°C for 15 seconds.
Sterilization involves heating milk at 71.6°C for 15 seconds.
True
Which of the following methods is NOT used to assess the bacteriological standards of milk?
Which of the following methods is NOT used to assess the bacteriological standards of milk?
What is the purpose of adding methylene blue to raw milk in the methylene blue reduction test?
What is the purpose of adding methylene blue to raw milk in the methylene blue reduction test?
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In the methylene blue reduction test, what does a white color indicate?
In the methylene blue reduction test, what does a white color indicate?
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What does a fast reduction in color in the methylene blue reduction test indicate?
What does a fast reduction in color in the methylene blue reduction test indicate?
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In the Litmus Milk Reaction, the enzyme β-galactosidase is responsible for the fermentation of lactose.
In the Litmus Milk Reaction, the enzyme β-galactosidase is responsible for the fermentation of lactose.
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The Litmus milk reaction can be used to test for the presence of microorganisms.
The Litmus milk reaction can be used to test for the presence of microorganisms.
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What does a pink color in the Litmus milk reaction indicate?
What does a pink color in the Litmus milk reaction indicate?
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The Litmus milk reaction can be used to detect gas production by microorganisms.
The Litmus milk reaction can be used to detect gas production by microorganisms.
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What does the formation of a hard acid curd in the Litmus Milk Reaction indicate?
What does the formation of a hard acid curd in the Litmus Milk Reaction indicate?
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The alkaline reaction in the Litmus Milk reaction is characterized by the production of ammonia.
The alkaline reaction in the Litmus Milk reaction is characterized by the production of ammonia.
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The alkaline reaction in the Litmus Milk reaction is characterized by a blue color.
The alkaline reaction in the Litmus Milk reaction is characterized by a blue color.
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In the Litmus milk reaction, the proteolysis process involves the breakdown of proteins into their basic building blocks.
In the Litmus milk reaction, the proteolysis process involves the breakdown of proteins into their basic building blocks.
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The Litmus milk reaction is a reliable indicator of the presence of specific pathogenic bacteria in milk.
The Litmus milk reaction is a reliable indicator of the presence of specific pathogenic bacteria in milk.
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The Litmus milk reaction is a useful tool for assessing the overall quality of milk.
The Litmus milk reaction is a useful tool for assessing the overall quality of milk.
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In the Litmus milk reaction, what reaction is indicated by a deep purple color in the upper protein of the tube?
In the Litmus milk reaction, what reaction is indicated by a deep purple color in the upper protein of the tube?
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A translucent brown whey in the Litmus milk reaction indicates a negative result.
A translucent brown whey in the Litmus milk reaction indicates a negative result.
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In the Litmus milk reaction, which of the following reactions is associated with the production of bubbles in the coagulated milk?
In the Litmus milk reaction, which of the following reactions is associated with the production of bubbles in the coagulated milk?
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A negative result in the Litmus milk reaction means that the color and consistency of the milk remain unchanged.
A negative result in the Litmus milk reaction means that the color and consistency of the milk remain unchanged.
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The Litmus milk reaction provides a definitive identification of specific bacterial species present in the milk.
The Litmus milk reaction provides a definitive identification of specific bacterial species present in the milk.
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The Litmus milk reaction is primarily used to evaluate the microbial quality of pasteurized milk.
The Litmus milk reaction is primarily used to evaluate the microbial quality of pasteurized milk.
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Which of the following can be used to differentiate between Litmus milk reactions caused by different bacterial species?
Which of the following can be used to differentiate between Litmus milk reactions caused by different bacterial species?
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Study Notes
Bacteriological Analysis of Milk
- Milk is a nutrient medium for both pathogenic and non-pathogenic bacteria
- Pasteurization: Heating at 62.5°C for 30 minutes
- Sterilization: Arnold Heating at 71.6°C for 15 seconds
- Bacteriological Standards: Determining total colony counts using pour plates
- Coliform tests
- Culture of pathogens
- Testing for heat-sensitive phosphatase enzyme via direct microscopy.
Direct Microscopy
-
Procedure:
- Xylene hydrolysis for lipid extraction
- Air-dry sample
- Alcohol fixation
- Stain with methylene blue
- Results: Observe bacteria types (e.g., Streptococcus, Bacillus, Lactobacilli) and their reactions to heat or other treatments.
Methylene Blue Test
- Add 1 ml of raw milk and 1 ml of methylene blue to a sample.
- Add 5 drops of oil
- Observe changes in color (from blue to white) indicating microbial activity levels
- Reduction in color in short time = high microbial count
- Reduction in color in long time = low microbial count
- The longer it takes for the color to change, the better the quality, e.g; 2 hours - poor, 6-8 hours - fair, 8 hours plus - excellent quality
Litmus Milk Reaction
-
Lactose Fermentation:
- Enzyme: β-galactosidase
- Lactose → glucose + galactose → pyruvic acid → lactic acid
- pH change: neutral (purple) to acidic (pink)
- Gas Production: Microorganisms hydrolyze proteins, causing gas production.
- Curd Formation: Microorganisms produce acid, causing coagulation of milk proteins ("hard acid curd" or "soft curd").
Alkaline Reaction (Casein)
- Proteolysis (peptonization): Milk proteins (primarily casein) are hydrolyzed into amino acids.
- pH Changes: Resulting in an alkaline pH and deep purple color, particularly in the upper part of the test tube.
- The medium loses its body, becoming translucent brown (whey)
- Hydrolysis of protein to amino acids is observed.
Reactions of Litmus Milk
- Acidic pH: Litmus milk turns pink or red.
- Alkaline pH: Litmus milk turns purple or blue.
- Reduction: Litmus milk turns white.
- Acid Curd: Formation of hard curd with clear supernatant.
- Digestion: Dissolution of the clot with a clear, gray solution.
- Rennet Curd: Soft curd followed by peptonization.
- Gas Production: Bubbles form in coagulated milk.
- Negative test: Color and consistency remain the same.
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Description
This quiz covers the principles and methods of bacteriological analysis of milk, including pasteurization, sterilization, and various microbial tests. Participants will explore procedures such as direct microscopy and the methylene blue test to assess microbial activity levels in milk. Test your knowledge on the standards and practices in milk safety and quality control.
