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What is the primary component of milk by percentage?
What is the primary component of milk by percentage?
Which of the following microorganisms is commonly responsible for spoilage in milk?
Which of the following microorganisms is commonly responsible for spoilage in milk?
What is the pH level typical for milk?
What is the pH level typical for milk?
Which factor does NOT affect the quality of milk production?
Which factor does NOT affect the quality of milk production?
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What is the role of lactic acid bacteria in dairy production?
What is the role of lactic acid bacteria in dairy production?
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What type of microorganisms are considered pathogenic in milk?
What type of microorganisms are considered pathogenic in milk?
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Which of the following is NOT a component of milk solids?
Which of the following is NOT a component of milk solids?
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Which of the following is a method for reducing microbial contamination in milk?
Which of the following is a method for reducing microbial contamination in milk?
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What is the main reason for recommending the exclusion of first quantities from the milking process?
What is the main reason for recommending the exclusion of first quantities from the milking process?
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Which vitamin is NOT commonly found in milk?
Which vitamin is NOT commonly found in milk?
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What type of microorganisms are coliforms known to be?
What type of microorganisms are coliforms known to be?
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Which spoilage microorganism is capable of producing heat-stable enzymes?
Which spoilage microorganism is capable of producing heat-stable enzymes?
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Which temperature classification best describes microorganisms that can grow near zero degrees Celsius?
Which temperature classification best describes microorganisms that can grow near zero degrees Celsius?
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What happens to the activity of acid-producing bacteria at low temperatures?
What happens to the activity of acid-producing bacteria at low temperatures?
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Which of the following pathogens is NOT commonly associated with raw milk?
Which of the following pathogens is NOT commonly associated with raw milk?
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What is an important characteristic of coliforms related to milk spoilage?
What is an important characteristic of coliforms related to milk spoilage?
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Which organism is primarily responsible for spoilage in refrigerated milk?
Which organism is primarily responsible for spoilage in refrigerated milk?
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What is the effect of fast pasteurization on coliforms?
What is the effect of fast pasteurization on coliforms?
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Which organism is considered an indicator of milk contamination?
Which organism is considered an indicator of milk contamination?
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What role do hygienic milk production practices play?
What role do hygienic milk production practices play?
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What does the presence of ALP in milk indicate?
What does the presence of ALP in milk indicate?
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Which type of bacteria can survive the pasteurization process and potentially cause spoilage?
Which type of bacteria can survive the pasteurization process and potentially cause spoilage?
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What is a potential outcome of thermoduric bacteria in milk?
What is a potential outcome of thermoduric bacteria in milk?
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Which bacteria group is known to cause defects such as fruity or rancid tastes in milk after pasteurization?
Which bacteria group is known to cause defects such as fruity or rancid tastes in milk after pasteurization?
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What does the presence of coliform bacteria in pasteurized milk suggest?
What does the presence of coliform bacteria in pasteurized milk suggest?
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Which of the following types of bacteria is particularly resilient due to its ability to form spores?
Which of the following types of bacteria is particularly resilient due to its ability to form spores?
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What may happen if milk is stored improperly after pasteurization?
What may happen if milk is stored improperly after pasteurization?
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Which bacteria are known for utilizing milk components and may lead to flavor changes?
Which bacteria are known for utilizing milk components and may lead to flavor changes?
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Which of these bacteria types typically does not thrive in the pasteurization heat?
Which of these bacteria types typically does not thrive in the pasteurization heat?
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What is a common consequence of bacterial activity after pasteurization?
What is a common consequence of bacterial activity after pasteurization?
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What temperature is typically maintained to enhance milk quality and shelf life immediately after milking?
What temperature is typically maintained to enhance milk quality and shelf life immediately after milking?
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What is a consequence of boiling milk regarding acid-producing bacteria?
What is a consequence of boiling milk regarding acid-producing bacteria?
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Which of the following bacteria is known to cause tuberculosis and is targeted during pasteurization?
Which of the following bacteria is known to cause tuberculosis and is targeted during pasteurization?
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Which pasteurization method involves treating milk at 62.85°C for 30 minutes?
Which pasteurization method involves treating milk at 62.85°C for 30 minutes?
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What effect does cooling milk have on thermoduric bacteria?
What effect does cooling milk have on thermoduric bacteria?
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What is the maximum temperature needed to inactivate Mycobacterium tuberculosis during pasteurization?
What is the maximum temperature needed to inactivate Mycobacterium tuberculosis during pasteurization?
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What is the purpose of the phosphatase test in milk processing?
What is the purpose of the phosphatase test in milk processing?
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What is primarily preserved when milk undergoes pasteurization?
What is primarily preserved when milk undergoes pasteurization?
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At what temperature is milk typically treated using the High Temperature Short Time method?
At what temperature is milk typically treated using the High Temperature Short Time method?
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What happens to the bacterial spores remaining in milk after boiling?
What happens to the bacterial spores remaining in milk after boiling?
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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
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(1) Lactic Acid Bacteria*
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Ferment lactose to lactic acid.
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Used as starters for various dairy products (e.g., yogurt).
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Examples: Lactococci (e.g., Lactococcus lactis), Lactobacilli (e.g., Lactobacillus casei), Leuconostoc (e.g., Leuconostoc lactis)
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(2) Coliforms*
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Facultative anaerobes, optimal growth at 37°C.
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Indicator organisms for pathogens.
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Spoilage microorganisms causing acid and gas production and degradation of milk proteins.
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Killed by pasteurization.
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Example: Escherichia coli.
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(3) Spoilage Microorganisms in Milk*
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Primarily psychrotrophic (can grow at low temperatures).
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Many are destroyed by pasteurization but some (e.g., Pseudomonas fluorescens, Pseudomonas fragi) produce heat-stable enzymes causing spoilage.
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Examples: Bacillus, Clostridium, Cornebacterium, Lactobacillus, Micrococcus, Streptococcus.
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(4) Pathogenic Microorganisms in Milk*
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Milk-borne diseases (e.g., tuberculosis, brucellosis, typhoid fever) have been reduced due to improved hygienic practices, pasteurization and milk handling.
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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
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Thermophilic bacteria: May survive and proliferate in refrigerated pasteurized milk, causing spoilage (e.g., Streptococcus thermophilus, Lactobacillus delbrueckii).
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Thermoduric bacteria: Endure heat treatment (e.g., Streptococcus spp., Enterococcus spp., Lactobacillus spp) causing flavor and quality changes.
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Psychrophilic bacteria: Spoilage defects appear after several days (eg. Alcaligenes, Pseudomonas, Lactococcus)
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Spore-forming bacteria: Can survive pasteurization, and cause spoilage defects (e.g., Bacillus, Clostridium).
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Coliform bacteria: Can survive pasteurization but have no significant effect.
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Description
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.
