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What are the primary products of lactose fermentation by coliform bacteria?
What are the primary products of lactose fermentation by coliform bacteria?
During the putrefactive period, which substance is primarily attacked by proteolytic bacteria?
During the putrefactive period, which substance is primarily attacked by proteolytic bacteria?
Coliform bacteria are beneficial in cheese production due to their ability to enhance flavor development.
Coliform bacteria are beneficial in cheese production due to their ability to enhance flavor development.
False
Name one condition in which the amount of lipase enzyme in milk may increase.
Name one condition in which the amount of lipase enzyme in milk may increase.
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The pH of milk during the putrefactive period typically ranges from 2-4.
The pH of milk during the putrefactive period typically ranges from 2-4.
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The breakdown of milk fat into fatty acids and glycerol is known as ______.
The breakdown of milk fat into fatty acids and glycerol is known as ______.
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What is the main product of acid fermentation in milk?
What is the main product of acid fermentation in milk?
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Which of the following is an example of a lactose-fermenting yeast?
Which of the following is an example of a lactose-fermenting yeast?
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Lactic acid bacteria are considered ______ anaerobes.
Lactic acid bacteria are considered ______ anaerobes.
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At approximately what temperature does casein precipitate due to lactic acid?
At approximately what temperature does casein precipitate due to lactic acid?
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Proteolysis is the process of breaking down milk fat into fatty acids and glycerol.
Proteolysis is the process of breaking down milk fat into fatty acids and glycerol.
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The curd formed during acid fermentation is typically characterized by visible signs of decomposition and gas rupture.
The curd formed during acid fermentation is typically characterized by visible signs of decomposition and gas rupture.
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The initial degradation of milk protein results in the formation of peptones and ______.
The initial degradation of milk protein results in the formation of peptones and ______.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Match the following microorganisms with their primary activity in milk:
Match the following microorganisms with their primary activity in milk:
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What is the typical pH range of milk during the putrefactive period?
What is the typical pH range of milk during the putrefactive period?
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What is the approximate pH of milk?
What is the approximate pH of milk?
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Milk is completely sterile throughout the entire milking process.
Milk is completely sterile throughout the entire milking process.
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What is the primary reason for the germicidal action of milk?
What is the primary reason for the germicidal action of milk?
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Heating milk at 60°C for 30 minutes enhances the anti-microbial activity of milk.
Heating milk at 60°C for 30 minutes enhances the anti-microbial activity of milk.
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Name two groups that bacteria in milk generally fall into.
Name two groups that bacteria in milk generally fall into.
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What is the main function of lactoferrin in the anti-microbial system of milk?
What is the main function of lactoferrin in the anti-microbial system of milk?
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The process by which changes are produced in milk due to the activity of microorganisms is known as _________.
The process by which changes are produced in milk due to the activity of microorganisms is known as _________.
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Which of the following is NOT a method used to detect changes in milk during fermentation?
Which of the following is NOT a method used to detect changes in milk during fermentation?
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The lactoperoxidase system requires peroxidase, thiocyanate, and ______ to produce hypothiocyanate.
The lactoperoxidase system requires peroxidase, thiocyanate, and ______ to produce hypothiocyanate.
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Match the fermentation periods with their descriptions:
Match the fermentation periods with their descriptions:
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How do polymorph nuclear leucocytes protect the udder from infection?
How do polymorph nuclear leucocytes protect the udder from infection?
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The level of lactoferrin in milk decreases during mastitis.
The level of lactoferrin in milk decreases during mastitis.
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Pathogenic organisms in milk have a significant impact on the milk's constituents, leading to economic losses.
Pathogenic organisms in milk have a significant impact on the milk's constituents, leading to economic losses.
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What are two ways milk can be contaminated by microorganisms?
What are two ways milk can be contaminated by microorganisms?
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What are the two main types of immunoglobulins that are present in milk?
What are the two main types of immunoglobulins that are present in milk?
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Match the following components of the anti-microbial system with their functions:
Match the following components of the anti-microbial system with their functions:
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Which of the following is NOT a result of proteolytic degradation?
Which of the following is NOT a result of proteolytic degradation?
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Sweet curdling is primarily caused by lactic acid-producing organisms.
Sweet curdling is primarily caused by lactic acid-producing organisms.
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What type of enzyme causes the coagulation of milk protein in sweet curdling?
What type of enzyme causes the coagulation of milk protein in sweet curdling?
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Ropy fermentation is caused by microorganisms that produce gum-like or sticky substances called ______.
Ropy fermentation is caused by microorganisms that produce gum-like or sticky substances called ______.
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Match the following microorganisms with their associated spoilage type:
Match the following microorganisms with their associated spoilage type:
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Which of the following conditions favors ropy fermentation?
Which of the following conditions favors ropy fermentation?
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Ropiness in milk caused by mastitis is due to bacterial capsular material.
Ropiness in milk caused by mastitis is due to bacterial capsular material.
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Besides bacteria, what other type of microorganism is named in the content as a proteolytic organism?
Besides bacteria, what other type of microorganism is named in the content as a proteolytic organism?
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Which of the following organisms is NOT a typical cause of alkaline fermentation in milk?
Which of the following organisms is NOT a typical cause of alkaline fermentation in milk?
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Ropiness in milk is always evident immediately when milk is drawn from the udder.
Ropiness in milk is always evident immediately when milk is drawn from the udder.
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What enzyme is primarily responsible for the breakdown of lecithin in fat globule membranes, leading to bitty or broken cream?
What enzyme is primarily responsible for the breakdown of lecithin in fat globule membranes, leading to bitty or broken cream?
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In alcoholic fermentation, yeast enzymes break down lactose into alcohol and ______
In alcoholic fermentation, yeast enzymes break down lactose into alcohol and ______
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Match the following milk defects with their primary cause:
Match the following milk defects with their primary cause:
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Study Notes
Milk Fermentation
- Milk composition includes water, carbohydrates, proteins, fats, vitamins, and minerals, with a pH of approximately 6.8.
- Milk is considered an excellent food for humans and a good growth medium for microorganisms.
- Milk is sterile when secreted by the udder, but contamination occurs before exiting the udder.
- Most bacteria in milk from healthy animals are harmless and few in number.
- Milk can become contaminated during milking, handling, storage, transport, and processing from diseased animals, equipment, or polluted environments.
- Bacteria in milk are categorized into two groups: pathogenic and non-pathogenic.
Pathogenic Organisms (Public Health Importance)
- Cause diseases in humans and/or animals.
- Have a minimal effect on milk components.
Non-Pathogenic Organisms (Economic Importance)
- Cause changes in milk components, leading to economic losses.
- Include lactic acid bacteria, spore-forming organisms, and those causing abnormal conditions or taints.
Normal Fermentation of Milk
- Fermentation is a process of change in milk due to microorganisms.
- Raw milk contains microorganisms that cause various changes when left at room temperature.
- Normal fermentation of milk is usually observed in stages.
Germicidal Period
- Immediately after milking, there is a period of no bacterial growth.
- Some bacterial numbers may decrease.
- This period is due to the presence of antimicrobial components in milk.
- The period's duration varies based on the animal and initial microbial count.
Souring Period
- Active growth of microorganisms, particularly lactic acid-producing bacteria.
- Convert lactose into lactic acid (with other minor changes).
- Process may continue for several hours or days, stopping when acid production inhibits further microbial growth.
- Evidence of acid production is visible as a sour flavor and curd formation.
Neutralization Period
- High acid concentrations inhibit most bacteria.
- Yeasts and molds become more active, reducing the acidity.
- Milk changes from acidic to neutral or slightly alkaline.
Putrefactive Period
- Active proteolytic bacteria, which break down milk proteins.
- This phase results in the production of bitter-tasting fluids with a foul odor.
- Milk is unfit for human consumption at this stage.
Specific Fermentation of Milk
- Acid fermentation (souring) is the most prevalent type in dairy.
- Lactic acid bacteria are used to produce cultured dairy products like yogurt, cheese, and cultured cream.
- Milk is also susceptible to abnormal changes or spoilage.
Classification of Lactic Acid Producing Bacteria
- Homofermentative (Homolactic): produce primarily lactic acid.
- Heterofermentative (Heterolactic): produce lactic acid and other byproducts (e.g., alcohol and gases).
Acid and Gas Fermentation ("Souring and Gassiness")
- Microorganisms ferment lactose to lactic acid and gases, forming spongy curds.
- Milk protein (casein) formation is affected by the produced acid.
- Gas production causes the curd to be spongy and float to the top.
Coliforms
- Contaminate milk from manure, soil, contaminated water, and animal feed.
Lactose-Fermenting Yeasts
- Some yeast species can ferment lactose to produce acids, gases, and alcohol.
Gas-Forming Clostridia
- Found in milk, they ferment lactose when held in limited air or reduced oxygen environments, producing significant amounts of gas and acid.
Lipolytic Fermentation
- Milk fat (triglycerides) are broken down by enzymes (lipases) into fatty acids and glycerol.
- This process occurs in high-fat dairy products like cream and whole milk and is influenced by the presence of lipase enzymes and environmental factors.
Proteolytic Fermentation
- Proteins are broken down by protein-splitting enzymes into water-soluble compounds such as peptones and peptides.
- This process results in the production of bitter tastes and putrid odors in the milk.
- Various bacteria and molds contribute to this process.
Sweet Curdling
- Most common in pasteurized/heated milk with low bacterial counts and low temperatures.
- Milk proteins coagulate due to the presence of rennin-like enzymes.
Ropy ("Slimy") Fermentation
- Characterized by long threads of milk.
- Caused by microorganisms producing sticky substances.
- Typically occurs under low temperature and higher acidity storage conditions.
Alkaline Fermentation
- Occurs due to alkali-producing microorganisms.
- A reaction happens without proteolysis.
- Organisms attack salts of organic acids, resulting in an alkaline environment.
Alcoholic Fermentation
- Yeasts ferment lactose into alcohol and CO2.
- Used in the production of certain dairy products like kefir.
Bitty or Broken Cream
- Occurs in various milk types.
- Milk cream layer breaks during shaking, causing non-homogeneous mixing.
- Enzyme lecithinase breaks down membranes, allowing fat globules to aggregate, leading to separated cream.
Flavor Changes (Abnormal Flavor)
- Flavor changes in milk due to various microorganisms, factors like feed, environmental conditions, or storage time.
- Milk exhibiting sour, bitter, or other unusual flavors is often considered undesirable.
Color Changes
- Abnormal colors can result from microorganisms secreting colored substances or substances changing color in acidic milk environments.
- Various microorganisms are implicated in the color changes.
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Description
Test your understanding of lactose fermentation and the role of coliform bacteria in dairy science. This quiz covers important concepts such as the products of fermentation, proteolytic bacterial activities, and the behavior of enzymes in milk. Challenge yourself with questions about milk composition and fermentation processes.
