Dairy Science - Milk Fat Composition & Properties
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Questions and Answers

What constitutes the majority of milk fat?

  • Mono-glycerides
  • Free fatty acids
  • Di-glycerides
  • Triglycerides (correct)

How does the fat content in milk contribute to dairy products?

  • It reduces the creamy texture.
  • It stabilizes the milk without flavor impact.
  • It increases the water content.
  • It provides rich-tasting qualities. (correct)

What is the role of the protein membrane surrounding milk fat globules?

  • To increase fat globule size.
  • To enhance the fatty acid concentration.
  • To decrease the fat content.
  • To contribute to the stability of the emulsion. (correct)

Which component represents the lowest concentration in milk fat?

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

What characteristic of milk fat varies based on its fatty acid composition?

<p>Temperature stability (A)</p> Signup and view all the answers

What is the melting point of Butyric acid?

<p>-7.9 °C (D)</p> Signup and view all the answers

Which fatty acid has the highest percentage of total fatty-acid content in milk fat?

<p>Palmitic acid (A)</p> Signup and view all the answers

What is a characteristic of Oleic acid at room temperature?

<p>It is liquid. (A)</p> Signup and view all the answers

Which fatty acid is classified as an unsaturated fatty acid?

<p>Linoleic acid (D)</p> Signup and view all the answers

Which of the following fatty acids has a melting point of +53.8 °C?

<p>Myristic acid (C)</p> Signup and view all the answers

Which fatty acid can be found in milk fat at a percentage of up to 1.0?

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

What change does heat treatment have on the triacylglycerols in the core of milk fat globules (MFG)?

<p>They are not affected. (C)</p> Signup and view all the answers

Which fatty acid has a melting point of -5.0 °C?

<p>Linoleic acid (C)</p> Signup and view all the answers

What is the primary component of the milk fat globule membrane (MFGM)?

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

What prevents the milk fat globules from immediate flocculation and coalescence?

<p>The properties of the fat globule membrane (D)</p> Signup and view all the answers

Which phenomenon is a physical instability process associated with emulsions?

<p>Flocculation (A)</p> Signup and view all the answers

During fat destabilization, what is primarily formed within the product?

<p>A continuous internal fat network (D)</p> Signup and view all the answers

What is the thickness range of the milk fat globule membrane (MFGM)?

<p>20-80 nm (C)</p> Signup and view all the answers

What is a result of heat-induced deactivation of the agglutination mechanism in milk?

<p>Interaction of fat globules through MFGM proteins (D)</p> Signup and view all the answers

What does partial coalescence of fat globules refer to?

<p>Fat globules clumped loosely but not fully merged (D)</p> Signup and view all the answers

Which of the following is NOT a major phenomenon associated with the instability of emulsions?

<p>Saturation (D)</p> Signup and view all the answers

What happens to milk fat when it is heated?

<p>Fats begin to melt, leading to separation from aqueous phase. (B)</p> Signup and view all the answers

Which fatty acid is specifically responsible for the rancid flavor in milk fat from ruminant animals?

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

What is the primary effect of adding MFGM to whipping cream?

<p>It increases the foaming rate. (B)</p> Signup and view all the answers

What does lipolysis of milk fat mainly cause?

<p>Increased concentration of short-chain fatty acids. (D)</p> Signup and view all the answers

What is the consequence of phase breaking in emulsions?

<p>The dispersed phase separates completely from the continuous phase. (C)</p> Signup and view all the answers

How does MFGM impact bread quality?

<p>It improves moisture retention and nutritional value. (D)</p> Signup and view all the answers

What contributes to the development of flavor in butter upon heating?

<p>Formation of lactones from C14:0 and C16:0 fatty acids. (A)</p> Signup and view all the answers

What is a common result of lipolysis in dairy products?

<p>Development of unpleasant taste and aroma. (B)</p> Signup and view all the answers

What is the process called when fat globules separate from milk serum?

<p>Cream separation (C)</p> Signup and view all the answers

Which component is located at the core of the milk fat globule?

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

What is responsible for the cold agglutination of fat globules in milk?

<p>Immunoglobulin M (IgM) (B)</p> Signup and view all the answers

Which layer is beneath the liquid ordered domain in the milk fat globule membrane?

<p>Monolayer of phospholipids (B)</p> Signup and view all the answers

What is the average diameter range of milk fat globules found in milk?

<p>4 to 6 µm (B)</p> Signup and view all the answers

Which of the following components is NOT typically found in the core of the milk fat globule?

<p>Proteins (D)</p> Signup and view all the answers

What effect does heating IgM to certain time-temperature combinations have on cold agglutination?

<p>Prevents the clustering of fat globules (C)</p> Signup and view all the answers

Which layer is found directly beneath the monolayer of phospholipids in the milk fat globule membrane?

<p>Bilayer of polar lipids (A)</p> Signup and view all the answers

What is the primary constituent class of total lipids in milk?

<p>Triglycerides (D)</p> Signup and view all the answers

Which process involves the upward movement of dispersed oil droplets in an oil/water emulsion?

<p>Creaming (A)</p> Signup and view all the answers

What characterizes flocculation in fat globules?

<p>Fat globules cluster but retain their identity. (C)</p> Signup and view all the answers

How are phospholipid classes expressed in the context of total phospholipids in milk?

<p>As a range of percentages (A)</p> Signup and view all the answers

Which of the following lipid classes is present in the least amount in milk?

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

What is the difference between coalescence and partial coalescence of fat globules?

<p>In coalescence, fat globules are completely fused, while in partial, they are only clumped. (B)</p> Signup and view all the answers

Which constituent is the dominant phospholipid in milk?

<p>Phosphatidyl choline (C)</p> Signup and view all the answers

What happens to fat globules during gravitational separation?

<p>They either cream upwards or sediment downwards. (C)</p> Signup and view all the answers

Flashcards

Milk Fat Percentage

Milk typically contains roughly 3.5% fat by weight. This fat content contributes to the texture, taste, and overall quality of dairy products.

Economic Importance of Milk Fat

The fat content of milk has significant economic value because it influences the price of milk, cheese, butter, and other dairy products.

Triglycerides

Triglycerides make up the majority of milk fat (96-98%). These complex molecules are formed from three fatty acids attached to a glycerol backbone.

What determines milk fat properties?

The composition of fatty acids in milk fat influences its properties. This includes the length of fatty acid chains, the presence of double bonds, and the type of fatty acid.

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Milk Lipids' Phases

Milk lipids are found in three distinct phases: fat globules (the actual fat droplets), fat globule membrane (a protein layer surrounding each globule), and the serum phase (the watery part of milk).

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MFGM

The membrane surrounding milk fat globules. It's composed mainly of protein and phospholipids and helps stabilize milk fat.

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MFGM Composition

The MFGM is made up mostly of proteins (70%) and phospholipids (25%). It also contains smaller amounts of cerebrosides, cholesterol, nucleic acids, enzymes, trace elements, and bound water.

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MFGM Function

The MFGM helps stabilize milk fat by decreasing the surface tension between the fat globules and the surrounding milk serum. This prevents the fat globules from clumping together.

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Fat Destabilization

The process of fat globules clustering and clumping together, leading to the formation of a network structure in dairy products.

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Partial Coalescence

Fat globules partially clump together but don't completely fuse.

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Flocculation

Fat globules loosely clump together.

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Coalescence

Fat globules completely fuse together.

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Creaming

Fat globules move upwards due to gravity.

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Triglycerides in Milk

The most abundant type of lipid in milk, comprising around 62% of the total lipids.

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Phospholipids in Milk

A vital component of milk, comprising 26-31% of the total lipids, responsible for forming membranes and regulating milk properties.

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Gravitational Separation

The movement of fat droplets in milk under the influence of gravity, leading either to creaming (upward movement) or sedimentation (downward movement).

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Aggregation

The process of fat globules in milk coming together into clusters, encompassing both flocculation (reversible clumping) and coalescence (irreversible merging).

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Milk fat globule membrane (MFGM)

A protective coating on the surface of milk fat globules that keeps the fat stable in the watery milk environment.

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What are triglycerides?

The main component of milk fat, they are molecules made of glycerol and three fatty acids.

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What is homogenization?

A process where milk fat globules are broken down into smaller particles, preventing them from separating as cream.

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What is cream separation?

The process where fat globules rise to the top of milk, forming cream.

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How does IgM affect cream separation?

Immunoglobulin M (IgM) in milk forms a complex with lipoproteins in the MFGM, causing fat globules to clump together and rise faster, accelerating cream separation.

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What are the effects of heating on cream separation?

Heating milk denatures IgM, slowing down the cold agglutination process and thus reducing cream separation.

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What are the functions of MFGM?

The MFGM protects the fat globule, prevents fat globule aggregation, and acts as a barrier to lipase enzymes that could break down the fat.

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What is the difference between liquid ordered and liquid disordered domains in the MFGM?

The liquid ordered domain is more tightly packed and rigid, while the liquid disordered domain is more fluid and flexible. The arrangement affects membrane properties.

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What is a harder and less soluble cream layer formed due to?

This layer is formed due to stronger interactions than agglutinin-mediated mechanism.

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What happens to milk fat as it is heated?

The fats melt and separate from the aqueous phase of milk due to their different melting temperatures.

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What is lipolysis?

The breakdown of milk lipids, primarily due to the action of natural milk lipase.

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What is the effect of lipolysis on milk products?

It increases the concentration of short-chain fatty acids, leading to an unpleasant taste and aroma (rancidity).

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How does MFGM affect whipping cream?

Adding MFGM increases the foaming rate, resulting in a creamier texture.

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What role does MFGM play in bread?

It prevents moisture loss and migration, reducing bread aging and hardening.

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How does MFGM benefit infant formula?

Adding MFGM as a natural emulsifier is linked to better cognitive development in infants.

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What is 'breaking' in terms of emulsions?

It's the complete separation of the dispersed phase (e.g., fat globules) from the continuous phase (e.g., water) in an emulsion.

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What are milk fat's main components?

Milk fat is mostly composed of triacylglycerols, which are molecules formed by three fatty acids attached to a glycerol backbone.

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What's the impact of heat treatment on milk fat?

Heat treatment doesn't significantly alter the triacylglycerols in the core of milk fat globules.

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Saturated fatty acids

Saturated fatty acids have no double bonds between their carbon atoms. They are typically solid at room temperature and contribute to the richness and texture of dairy products.

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Unsaturated fatty acids

Unsaturated fatty acids have at least one double bond between their carbon atoms. They are typically liquid at room temperature and contribute to the flavor and smoothness of dairy products.

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Butyric acid

A short-chain saturated fatty acid found in milk fat, responsible for its distinctive taste and aroma.

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Oleic acid

A common unsaturated fatty acid in milk fat, contributes to its fluidity and smooth texture.

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Linoleic acid

A polyunsaturated fatty acid found in milk fat, important for healthy fats.

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Arachidonic acid

A polyunsaturated fatty acid found in milk fat, important for brain function and development.

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Study Notes

Dairy Science - Milk Fat Composition, Chemistry & Properties

  • Milk contains approximately 3.5% (w/v) fat.
  • Milk fat contributes to the development and quality (soft, watery, flat, hard) of dairy products.
  • Milk fat is economically important due to its characteristics.
  • Milk fat exists as microscopic globules with a lipoprotein membrane.
  • This membrane stabilizes milk's oil-water emulsion.

Milk Fat Composition (continued)

  • More than 400 fatty acid types are identified in milk.
  • Only a small fraction exists above 1% (by mass).
  • Triglycerides (96-98%) comprise the main constituent of milk fat.
  • Milk fat also includes mono- (0.4%), di-glycerides (2%)
  • and minor components like cholesterol (<0.5%), sphingolipids (1%), and phospholipids.
  • Free fatty acids (0.1%) are also present.

Milk Fat Properties (continued)

  • Fatty acids may differ in chain length, saturation, double bonds, and configuration.
  • Milk fat properties depend on fatty acid composition.
  • Triglycerides are non-polar and act as solvents for other nonpolar substances (sterols, carotenoids, tocopherol).
  • Other polar lipids in milk fat include phospholipids.
  • Milk lipids exist in three phases: fat globules, fat globule membrane, and milk serum.

Distribution of Lipids in Milk

  • Constituent: Location in Milk
  • Triglycerides Fat globule
  • Phospholipids (Lecithin, etc) Fat globule membrane & milk serum
  • Sterols Fat globule, fat globule membrane, milk serum
  • Free fatty acids Fat globule & milk serum
  • Waxes Fat globule
  • Fat-soluble vitamins Fat globule

Heat-Induced Changes in Milk Fat

  • Interactions during heating are stronger than agglutinin-mediated mechanisms, resulting in a harder, less soluble cream layer.
  • This can be rejected by consumers.
  • Milk fat, comprised of various triglycerides that melt at different temperatures, separates from the aqueous phase upon heating.
  • Lipolysis and autoxidation of milk fat may occur upon heating.
  • C14:0 and C16:0 β-hydroxy fatty acids form lactones, enhancing butter flavor.

Milk Fat Globule Membrane (MFGM)

  • MFGM accounts for 2-6% of fat globules and has different characteristics than milk fat and plasma.
  • It's a 10-50 nm thick tri-layer membrane surrounding fat globules.
  • The membrane contains mainly protein (70%), phospholipids (25%), along with cerebrosides, cholesterol, nucleic acids, enzymes, trace metals, and bound water.
  • Certain enzymes (alkaline phosphatase, xanthine oxidase) and minerals (iron, copper) are also found in this membrane.
  • MFGM lowers the lipid-serum interface (1-2.5 mN/m) and prevents flocculation and coalescence.
  • It also protects globules from enzymatic action.

Other Milk Fat Properties

  • Surface Tension: Important for emulsification, foaming, and spreading properties; influenced by composition, temperature, and proteins/emulsifiers; typical values at 20°C are 25-35 mN/m.
  • Fat Destabilization: Necessary for butter, cream, and ice cream structure formation; involves clustering and clumping (partial coalescence) of fat globules to create a continuous fat network/matrix structure. Physical instability includes flocculation, creaming, coalescence, and breaking.
  • Refractive Index: Degree light passes through liquid fat; a characteristic of milk fat; range is 1.4537-1.4578; low value in cow's milk due to high saturated glycerides and short-chain acids.
  • Crystallization Behavior: Milk fat is liquid above 40°C and solid below -40°C; a mixture of crystals and oil (oil as continuous phase); many triglycerides make it complex; crystals can't grow larger than globule diameter; flocculation into a network giving globules rigidity.
  • Autoxidation: Generates hydroperoxides that decompose into undesirable-tasting/smelling compounds (rancid). This can be induced by metal (e.g. copper) or light exposure. Milk fat is resistant due to high saturated fatty acids and antioxidants (α-tocopherol and β-carotene). MFGM protects against lipolysis and oxidation.
  • Homogenization: Prevents creaming by reducing fat globule size and distribution. There is a new membrane that forms.
  • Cream separation: Fat globules separating from milk serum. Different densities. Immunoglobulins and cold agglutination are involved.
  • Fat as an emulsion: Fat distributed in a continuous aqueous phase (oil-in-water); membrane prevents fat globule merging.
  • Color & Antioxidant Potential: Fat color depends on carotene content (variation by animal species/breed/diet). Cow's milk yellow due to carotene. Buffalo milk has no carotene. Antioxidants like cholesterol, phospholipids protect shelf life of ghee.
  • Commercial Uses of MFGM: Added to whipping cream to improve foaming; a bread improver; to infant formulas as natural emulsifier.

Lipid Classification

  • Milk fat constituents such as Triglycerides, Diglycerides, Monoglycerides, Sterols, Free fatty acids, Phospholipids, Sphingomyelin, Phosphatidylcholine, Phosphatidyl ethanolamine, Phosphatidyl inositol, Phosphatidylserine, Glucosylceramide, and Lactosylceramide are also important components.

Important Terms for Milk Processing

  • Creaming: Upward movement of dispersed oil droplets due to density difference.
  • Flocculation: Reversible agglomeration of fat globules with no loss of individual globule identity.
  • Coalescence: Aggregation or clustering of fat globules with loss of individual globule identity.
  • Breaking (or Phase Separation): Complete separation of the dispersed phase from the continuous phase.

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Explore the intricate composition and properties of milk fat in this quiz. Learn about the various types of fatty acids present in milk and their impacts on dairy products. This quiz covers essential concepts in dairy science related to milk fat's chemistry and economic significance.

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