Microbiology of Dairy Products

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Questions and Answers

What type of bacteria is characterized as facultative anaerobes?

_Streptococcus_

_E.coli_ (correct)

_Clostridium_

_Pseudomonas_

What is the typical shelf life of pasteurized milk at refrigerator temperature?

1-2 weeks

1-3 days

3-15 days (correct)

20-30 days

Which bacteria is known to produce toxins that can attack the nervous system?

_E.coli_

_Staphylococcus aureus_

_Bacillus_

_Clostridium botulinum_ (correct)

What feature distinguishes spore-forming bacteria like Clostridium?

Can produce spores that resist harsh conditions Signup and view all the answers

What type of medium is used to isolate yeast and mold from dairy products?

Potato Dextrose Agar (PDA) Signup and view all the answers

Which type of microorganisms prefer low pH environments?

Yeast and mold Signup and view all the answers

What is the temperature used for pasteurization that lasts for 30 minutes?

63℃ Signup and view all the answers

Which bacteria are classified as obligate anaerobes?

Clostridium Signup and view all the answers

What is the primary function of starter cultures in dairy product manufacture?

To convert lactose to lactic acid Signup and view all the answers

Which of the following microorganisms is used as a yogurt starter culture?

Streptococcus thermophilus Signup and view all the answers

What effect does the production of lactic acid have on the pH of fresh milk?

Decreases pH to around 4.6 Signup and view all the answers

What distinguishes bacteria from yeast and molds?

Bacteria reproduce by binary fission. Signup and view all the answers

What is the role of lipase in milk spoilage?

It degrades milk fat causing spoilage Signup and view all the answers

Which type of fermentation produces only lactic acid as the main end product?

Homofermentative fermentation. Signup and view all the answers

What is the role of E.coli in food safety?

It is an indicator for fecal contamination. Signup and view all the answers

What is the isoelectric point (ISP) of casein in relation to pH?

Around 4.6 Signup and view all the answers

Which of the following can be used to reduce the growth of microorganisms?

Adding salt or sugar. Signup and view all the answers

Which type of microorganism is categorized as harmful and can cause spoilage in dairy products?

Pseudomonas Signup and view all the answers

What percentage of milk fat is composed of triglycerides?

89% Signup and view all the answers

Which organism is known to cause flat sour spoilage in food products?

Bacillus stearothermophilus Signup and view all the answers

What substances are produced by Lactococcus lactis subsp.lactis in milk that inhibit certain microorganisms?

Nisin (bacteriocin) Signup and view all the answers

What characteristic is true for yeast and molds but not for bacteria?

Their DNA is associated with histone proteins. Signup and view all the answers

Which of the following additives can help extend the shelf life of dry milk?

Removing water content. Signup and view all the answers

Which type of microbe replicates exclusively inside living cells?

Virus. Signup and view all the answers

Study Notes

Microbiology (Dairy)

Microorganisms are microscopic organisms, either single-celled (bacteria) or multi-celled (fungi/molds).
Microbiology is the study of microorganisms.
Anton van Leeuwenhoek is considered the father of microbiology, as he was the first to observe bacteria.
Microorganisms can be harmful or helpful, and some are useful as starter cultures in dairy products, converting lactose into lactic acid.
Starter cultures, such as those used in yogurt, are microorganisms added to dairy products to produce desired flavors and/or textures.
Examples of starter cultures used in dairy products include Streptococcus thermophilus and Lactobacillus bulgaricus.
- Butter starter cultures include Lactococcus lactis subsp.lactis, Lactococcus lactis subsp. cremoris, and Lactococcus lactis subsp.diacetylactis.

Dairy Microbiology (pH & Microorganism Activity)

Fresh milk has a pH of 6.6-6.8.
Adding starter cultures decreases the pH from 6.8 to 4.6, a point called the "isoelectric point (IP)" of casein, causing precipitation.
Microorganisms are involved in the production of flavors (like acetaldehyde), lipolytic activity (fat breakdown), and proteolytic activity (protein breakdown) in milk.
Microorganisms can also inhibit other microorganisms. Lactococcus lactis subsp lactis produces the bacteriocin Nisin.
Not all microorganisms are harmful. Some are involved in the spoilage of food and cause changes in appearance, odor, or viscosity.

Dairy Microbiology (Composition & Microorganisms)

Milk fat is composed primarily of triglycerides (3 fatty acids + glycerol), phospholipids and sterols.
Certain types of microorganisms are resistant to pasteurization, particularly the kind of lipase produced by Pseudomonas, compared to naturally occurring milk lipase.
Certain microbes are facultative anaerobes (E. Coli), while others are obligate anaerobes (Clostridium).
Spore-forming bacteria like Bacillus and Clostridium can survive pasteurization temperatures and cause problems later.
Shelf life is affected by the method of preservation; sterilized milk lasts longer than pasteurized milk at the refrigerator temperature.

Dairy Microbiology (Harmful Microorganisms)

Pseudomonas, a rod-shaped, aerobic bacterium, can cause spoilage and produce lipase enzymes.
E. coli, a facultative anaerobe, is commonly found in the intestines of animals and is often used as an indicator of fecal contamination in dairy products.
Clostridium, a spore-forming anaerobic bacteria, is a significant concern in dairy products due to its ability to cause late-stage spoilage, e.g., gassing.
Staphylococcus aureus, a coccus-shaped bacteria, can cause food poisoning.
Bacillus, Clostridium, etc., can cause food poisoning, through toxin production.

Dairy Microbiology (Factors Affecting Microorganisms)

Temperature is a key factor in microbial growth. Psychrophiles thrive in cold environments; mesophiles grow in moderate temperatures and thermophiles in hot temperatures.
pH affects microbial growth. Most bacteria prefer neutral pH (6.8-7.0), while yeasts and molds can tolerate acidic conditions.
Water activity is important because microbes need water to grow. Removing water content (producing dry milk; e.g) decreases microbial growth.
Salinity (adding salt) and sugar are antimicrobials.

Dairy Microbiology (Isolation & Growth)

PDA (Potato Dextrose Agar) is used to isolate yeasts and molds from dairy products. This is important for identifying specific organisms, allowing manufacturers to take action and add additives to prevent growth.
Water (87% of milk) is essential in microbial processes. Free water aids in microbial growth and can be reduced.

Dairy Microbiology (Types of Microorganisms)

Bacteria are unicellular prokaryotes multiplying largely by binary fission.
Yeasts are eukaryotes, are larger than bacteria, and reproduce by budding or fission.
Molds are multicellular eukaryotes forming hyphae (filaments).
Viruses are not cells; they infect cells.

Dairy Microbiology (Additional Considerations)

Different types of microorganisms can cause various forms of food poisoning and/or spoilage.
Microorganisms can produce toxins that negatively impact health when consumed.
Various preservation methods are in use for dairy products, including pasteurization, which involves heating to reduce the bacteria count, and sterilizing.

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Description

This quiz focuses on the study of microorganisms in dairy products, highlighting the role of starter cultures and their impact on pH levels. Learn about the beneficial microorganisms that contribute to the flavors and textures of various dairy items. Test your knowledge on the contributions of key figures like Anton van Leeuwenhoek and the importance of specific cultures.