Dairy Science: Lactose Fermentation and Bacteria
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Questions and Answers

What are the primary products of lactose fermentation by coliform bacteria?

  • Fatty acids and glycerol
  • Lactic acid and alcohol
  • Lactic acid and gases (CO2 and H2) (correct)
  • Peptones and peptides

During the putrefactive period, which substance is primarily attacked by proteolytic bacteria?

  • Fungi
  • Casein (correct)
  • Lactose
  • Lactic acid

Coliform bacteria are beneficial in cheese production due to their ability to enhance flavor development.

False (B)

Name one condition in which the amount of lipase enzyme in milk may increase.

<p>late lactation period or cystic ovary</p> Signup and view all the answers

The pH of milk during the putrefactive period typically ranges from 2-4.

<p>False (B)</p> Signup and view all the answers

The breakdown of milk fat into fatty acids and glycerol is known as ______.

<p>lipolysis</p> Signup and view all the answers

What is the main product of acid fermentation in milk?

<p>lactic acid</p> Signup and view all the answers

Which of the following is an example of a lactose-fermenting yeast?

<p>Candida pseudotropicals (C)</p> Signup and view all the answers

Lactic acid bacteria are considered ______ anaerobes.

<p>facultative</p> Signup and view all the answers

At approximately what temperature does casein precipitate due to lactic acid?

<p>25°C (A)</p> Signup and view all the answers

Proteolysis is the process of breaking down milk fat into fatty acids and glycerol.

<p>False (B)</p> Signup and view all the answers

The curd formed during acid fermentation is typically characterized by visible signs of decomposition and gas rupture.

<p>False (B)</p> Signup and view all the answers

The initial degradation of milk protein results in the formation of peptones and ______.

<p>peptides</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Putrefactive period = Decomposition of milk proteins via bacteria and fungi, producing a clear fluid. Acid fermentation = Conversion of lactose to lactic acid by bacteria. Lactic acid bacteria = Group of microorganisms responsible for producing lactic acid Casein = Main protein in milk that is curdled during acid fermentation</p> Signup and view all the answers

Match the following microorganisms with their primary activity in milk:

<p>E.coli = Lactose fermentation Pseudomonas fragi = Lipolytic fermentation Clostridium butyricum = Gas forming Oidium lactis = Lipolytic Fermentation</p> Signup and view all the answers

What is the typical pH range of milk during the putrefactive period?

<p>8-10</p> Signup and view all the answers

What is the approximate pH of milk?

<p>6.8 (B)</p> Signup and view all the answers

Milk is completely sterile throughout the entire milking process.

<p>False (B)</p> Signup and view all the answers

What is the primary reason for the germicidal action of milk?

<p>Presence of an anti-microbial system (D)</p> Signup and view all the answers

Heating milk at 60°C for 30 minutes enhances the anti-microbial activity of milk.

<p>False (B)</p> Signup and view all the answers

Name two groups that bacteria in milk generally fall into.

<p>Pathogenic organisms and non-pathogenic organisms</p> Signup and view all the answers

What is the main function of lactoferrin in the anti-microbial system of milk?

<p>To inhibit microbial growth by binding iron</p> Signup and view all the answers

The process by which changes are produced in milk due to the activity of microorganisms is known as _________.

<p>fermentation</p> Signup and view all the answers

Which of the following is NOT a method used to detect changes in milk during fermentation?

<p>Spectroscopic evaluation (B)</p> Signup and view all the answers

The lactoperoxidase system requires peroxidase, thiocyanate, and ______ to produce hypothiocyanate.

<p>hydrogen peroxide</p> Signup and view all the answers

Match the fermentation periods with their descriptions:

<p>Germicidal period = A period immediately after milking where there is no active growth of bacteria, sometimes with a decrease in numbers. Souring period = A period where milk becomes acidic due to bacterial activity. Neutralization period = A period where the acidity of milk decreases. Putrefactive period = A period where milk undergoes decomposition typically caused by proteolytic bacterial action.</p> Signup and view all the answers

How do polymorph nuclear leucocytes protect the udder from infection?

<p>By phagocyting invading bacteria (B)</p> Signup and view all the answers

The level of lactoferrin in milk decreases during mastitis.

<p>False (B)</p> Signup and view all the answers

Pathogenic organisms in milk have a significant impact on the milk's constituents, leading to economic losses.

<p>False (B)</p> Signup and view all the answers

What are two ways milk can be contaminated by microorganisms?

<p>From diseased animals or from handling during milking.</p> Signup and view all the answers

What are the two main types of immunoglobulins that are present in milk?

<p>IgA and IgG</p> Signup and view all the answers

Match the following components of the anti-microbial system with their functions:

<p>Immunoglobulins = Provide antibodies against pathogens Lactoferrin = Inhibits microbial growth by binding iron Polymorph nuclear leucocytes = Phagocytize invading bacteria Lactoperoxidase system = Kills bacteria by oxidative mechanisms</p> Signup and view all the answers

Which of the following is NOT a result of proteolytic degradation?

<p>Production of lactic acid (B)</p> Signup and view all the answers

Sweet curdling is primarily caused by lactic acid-producing organisms.

<p>False (B)</p> Signup and view all the answers

What type of enzyme causes the coagulation of milk protein in sweet curdling?

<p>rennin-like enzyme</p> Signup and view all the answers

Ropy fermentation is caused by microorganisms that produce gum-like or sticky substances called ______.

<p>capsular material</p> Signup and view all the answers

Match the following microorganisms with their associated spoilage type:

<p>Bacillus subtilis = Proteolysis and Sweet curdling Pseudomonas fluorescence = Proteolysis and Sweet curdling Alkaligenous viscousus = Ropy fermentation Streptococcus liquefaciens = Proteolysis and Sweet curdling</p> Signup and view all the answers

Which of the following conditions favors ropy fermentation?

<p>Low storage temperatures for at least 6 hours (A)</p> Signup and view all the answers

Ropiness in milk caused by mastitis is due to bacterial capsular material.

<p>False (B)</p> Signup and view all the answers

Besides bacteria, what other type of microorganism is named in the content as a proteolytic organism?

<p>moulds</p> Signup and view all the answers

Which of the following organisms is NOT a typical cause of alkaline fermentation in milk?

<p>Bacillus cereus (B)</p> Signup and view all the answers

Ropiness in milk is always evident immediately when milk is drawn from the udder.

<p>False (B)</p> Signup and view all the answers

What enzyme is primarily responsible for the breakdown of lecithin in fat globule membranes, leading to bitty or broken cream?

<p>Lecithinase</p> Signup and view all the answers

In alcoholic fermentation, yeast enzymes break down lactose into alcohol and ______

<p>CO2</p> Signup and view all the answers

Match the following milk defects with their primary cause:

<p>Ropiness (mastitis) = Directly drawn milk from udder Ropy Milk = Milk has stayed for 6-12h Bitty or broken cream = Lecithinase enzyme activity Alcoholic fermentation = Lactose-fermenting yeasts</p> Signup and view all the answers

Flashcards

Anti-microbial System in Milk

The natural defense system in milk that fights against bacteria. It's weakened by heating milk at 60°C for 30 minutes.

Immunoglobulin (Ig)

An antibody that protects against pathogens. It can be produced locally in the udder (IgA) or transferred from the bloodstream (IgG).

Polymorph Nuclear Leucocytes

White blood cells that engulf and destroy bacteria in the udder. Their number increases significantly during mastitis.

Lactoferrin

An iron-binding protein in milk that inhibits bacterial growth by depriving them of iron. Its levels rise during mastitis.

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Lactoperoxidase System (LPS)

An enzyme system in milk that kills bacteria using oxidative mechanisms. It requires lactoperoxidase, hydrogen peroxide, and thiocyanate.

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Passive Immunity

The process of transferring immunity from the mother to the offspring through milk, particularly colostrum.

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Mastitis

Inflammation of the udder, often caused by bacterial infection. It leads to increased somatic cell count, including polymorph nuclear leucocytes.

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Somatic Cell Count

A measure of the total number of cells in milk, primarily white blood cells. Elevated counts indicate infection.

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Pathogenic Organisms

Microorganisms that cause disease in humans or animals. They have a minimal impact on the composition of milk.

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Non-Pathogenic Organisms

Microorganisms that cause changes in milk constituents, leading to economic loss. These include lactic acid bacteria, spore-forming organisms, and organisms responsible for taints and abnormal milk conditions.

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Milk Fermentation

The natural changes that occur in milk due to the activity of microorganisms. This process involves the breakdown of milk components by microbes, leading to alterations in the milk's taste, texture, and other characteristics.

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Germicidal Period

This phase is characterized by a decrease in the number of bacteria present in the milk. Although bacteria are present, they are not actively multiplying during this phase.

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Souring Period

In this phase, lactic acid bacteria, primarily Lactobacillus and Streptococcus species, start to dominate the milk. This leads to the production of lactic acid, resulting in a sour taste and a decrease in pH.

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Neutralization Period

As the pH of milk decreases, the growth of lactic acid bacteria slows down. Other types of bacteria, such as proteolytic bacteria, may start to grow, leading to the formation of various compounds that can modify the flavor and aroma of the milk.

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Putrefactive Period

In this phase, putrefactive bacteria dominate, breaking down proteins into simpler compounds. This leads to a foul odor and an unpleasant taste in the milk. The milk becomes unfit for consumption.

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Coliforms in Dairy

Bacteria that ferment lactose, producing lactic acid and gases like carbon dioxide (CO2) and hydrogen (H2). Some may also break down proteins.

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Lactose Fermenting Yeasts

Yeast species that ferment lactose, producing acid, gases, and alcohol.

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Gas-Forming Clostridia

Anaerobic bacteria that produce spores and can ferment lactose to acid and gases, particularly when exposed to limited air.

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Lipolytic Fermentation (Lipolysis)

The breakdown of milk fat (triglycerides) into fatty acids and glycerol by the action of lipase enzymes.

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Lipase Enzyme

An enzyme naturally present in milk, its quantity increases during late lactation or with conditions like cystic ovary.

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Lipase-like Enzyme

Enzymes secreted by lipolytic microorganisms that can contaminate milk or dairy products, leading to fat breakdown.

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Proteolytic Fermentation (Proteolysis)

The breakdown of milk protein (casein) into smaller compounds by proteolytic organisms, which release proteinase enzymes.

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Peptones and Peptides

Initial products of milk protein breakdown by proteolytic enzymes, resulting in bitter flavors.

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Acid Fermentation (Souring)

The most common type of milk fermentation where lactose is converted into lactic acid by bacteria, resulting in a sour flavor and curdling.

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Lactic Acid Producing Organisms

A group of microorganisms responsible for converting lactose into lactic acid, causing the souring of milk. They are often used to make fermented dairy products like yogurt.

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Lactic Acid Fermentation

Lactic acid bacteria are capable of producing lactic acid from lactose, giving milk a sour flavor and eventually causing the milk proteins to curdle. This process can also be used to create cultured dairy products like yogurt.

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pH

A measure of the acidity or alkalinity of a substance. In milk, a pH of 8-10 indicates a high level of alkalinity, which is associated with the putrefactive period.

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Milk Solids

The solid component of milk, primarily composed of proteins, like casein, and fats.

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Casein

A type of protein found in milk. It is responsible for the curdling of milk when it becomes acidic.

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Specific Fermentation

A type of fermentation that occurs in milk due to the action of specific microorganisms. This can result in the formation of various products such as yogurt, cheese, and butter.

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Ropy Milk in Mastitis

A type of milk spoilage characterized by the formation of long, stringy strands when drawn directly from the udder.

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Ropy Milk (General)

A type of milk spoilage where milk becomes stringy after standing for 6-12 hours. This is caused by bacteria that produce a sticky substance.

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Alkaline Fermentation

Milk spoilage caused by bacteria that produce alkaline substances, raising the milk's pH. These bacteria break down organic acids like citric acid and urea.

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Alcoholic Fermentation

A type of milk spoilage resulting from the production of alcohol by yeasts that ferment lactose.

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Bitty or Broken Cream

A condition where the cream layer in milk breaks into small particles that don't mix homogenously. This happens due to the breakdown of fat globule membranes by certain bacteria.

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What are Proteolytic Organisms?

Proteolytic organisms are bacteria and fungi that break down proteins into smaller units, often leading to unpleasant odors. They degrade milk proteins into free amino acids, which then break down further into free amines and nitrogen, producing putrid smells.

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Aerobic Spore Formers

Aerobic spore formers, such as Bacillus subtilis, are bacteria that can survive harsh conditions and produce spores. They break down proteins in milk, leading to off-flavors and potential spoilage.

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Pseudomonas fluorescence

Pseudomonas fluorescence is a common bacterium in milk that causes a sweet, slightly fruity odor, but also contributes to proteolysis, ultimately leading to off-flavors.

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What is Sweet Curdling?

Sweet curdling refers to the coagulation of milk proteins, specifically casein, due to the action of renin-like enzymes produced by certain bacteria. This occurs at normal milk acidity and often happens in pasteurized milk.

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What Causes Sweet Curdling?

Sweet curdling is often caused by bacterial contamination in pasteurized milk or low-bacterial count raw milk. These bacteria often produce renin-like enzymes, which coagulate the casein in milk.

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What is Ropy Fermentation?

Ropy fermentation refers to the development of long strands or threads in milk or cream as it's poured. This happens due to the production of sticky substances (capsular material) by certain bacteria.

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What Conditions Favor Ropy Fermentation?

Ropy fermentation often develops at low storage temperatures. This is because the responsible bacteria thrive at cooler temperatures and produce more sticky material.

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Alkaligenous viscousus

Alkaligenous viscousus is a common bacteria that causes ropy fermentation. It produces a sticky substance that makes the milk thick and stringy.

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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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Milk Fermentation Lecture 4 PDF

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.

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