ANS 124: Fats in Milk

Are all liquid fat droplets the same size?

No, liquid droplets can range in size.

Liquid droplets can range in size from ___-___ micron diameter.

0.1 to 15 micron diameter

What is the average diameter range of a mammary epithelial cell?

~10-15 micron diameter

Describe how the liquid droplet diameter relates to the MEC diameter.

The MEC is pinching off/secreting (through pinocytosis) a fat droplet that is as big as itself sometimes.

Is milk composition the same among species?

No, it is highly variable among species.

The Milk Fat Globule Membrane comprises of various _________ from the apical membrane.

proteins

Milk is an "____ __ _______" emulsion.

oil in water

Homogenization of milk disrupts what in milk?

disrupts milk fat globules

What happens to the size of milk fat globules during homogenization?

MFG size decreases

What happens to the Surface Area of milk fat globules during homogenization?

Surface area increases by 10 fold.

What happens to the surface area-to-volume ratio of milk fat globules during homogenization?

increased surface area-to-volume ratio

What happens to the milk fat globules after milk is homogenized?

Casein Micelles and other whey proteins adsorb to milk fat globule membranes.

What is the purpose of casein micelles and other whey proteins adsorbing to milk fat globule membranes?

They help stabilize globules and make sure the fat droplets stay suspended instead of floating to the top.

Why do we homogenize milk before selling it at the grocery store?

because consumers want a consistent product

In the grocery store, how is the milk being sold exactly 3.3% fat (or whatever fat % they say on the label)?

They take away the fat in milk and add it back in to make it that specific percentage of fat.

Why do we take away the fat in milk and add it back in to make it that specific percentage of fat before selling it in grocery stores?

in order to make a consistent product

Compare the milk fat content of Holstein and Jersey cows.

Holsteins have fairly low milk fat content compared to Jersey cows.

Compare the volume of milk that the Holstein produces compared to the Jersey cows.

Holstein produces more volume of milk.

Since Holsteins produce more milk, overall, compare the total fat between Holsteins vs. Jerseys over a year.

Around the same amount of total fat over a year.

Milk Fat consists mainly of what component?

triglycerides

What percentage range of Milk Fat are triglycerides?

97-98%

In rats, what percentage of their milk fat is triglycerides? Why is it different?

87.5% in rats because they have higher free fatty acids.

Milk fat also consists of what 5 components besides Triglycerides?

Diacylglyceride

Monoacylglyceride

Free Fatty Acids

Phospholipids

Cholesterol

Short Chain Fatty Acids contain how many carbons?

<8 Carbons

Medium Chain Fatty Acids contain how many carbons?

8-14 Carbons

Long Chain Fatty Acids contain how many carbons?

≥16 Carbons

Short Chain Fatty Acids are mainly found in the milk of what animals?

Ruminants

Short Chain Fatty Acids are mainly found in the milk of ruminants due to the presence of what 2 molecules?

β-hydroxybutyrate (BHB)

Acetate

What way are Medium Chain Fatty Acids synthesized in the body? And where?

synthesized de novo (in the mammary epithelial cells)

Medium Chain Fatty Acids synthetized de novo from what 2 molecules?

acetate & glucose

Long Chain Fatty Acids enter mammary cells from what 2 ways?

From diet.

From adipose lipolysis (body reserves).

Explain why Short Chain Fatty Acids are mainly present in the milk of ruminants.

VFA from rumen are short carbon molecules. These go to the blood, and then the mammary gland to make Short Chain Fatty Acids.

Explain why Short Chain Fatty Acids are not present in the milk of monogastrics like humans, pigs and dogs.

Because monogastrics don't have VFA/Rumen

Compare the difference of Linoleic Acid amount in the milk of ruminants vs. monogastrics. (general)

Linoleic Acid is lower in ruminants.

What are 2 examples of food that contain a lot of unsaturated FAs?

Corn Oil

Olive Oil

Explain the diet of ruminants and what process in the rumen contributes to lower Linoleic Acid in their milk.

Ruminants eat a lot of unsaturated fatty acids (ex. corn silage). In the rumen, the microbes biohydrogenate it by saturating those FAs and getting rid of the double bonds.

How does biohydrogenation affect the fatty acid profile of steak?

Steak has more saturated FAs and not a lot of unsaturated FAs.

Explain the diet of pigs and how that contributes to their higher Linoleic Acid content in their milk and pork chops.

Pigs also eat corn with a lot of unsaturated FAs. However, they don't have a rumen to do biohydrogenation, so their milk and pork chops have a lot of unsaturated FAs in it.

Long Chain FAs with multiple double bonds can also be called what?

Polyunsaturated Fatty Acids (PUFAs)

Why would humans have milk that contains LCFAs/PUFAs?

If they've eaten fish or fish oil beforehand, their milk will have a lot of LCFAs/PUFAs because fish have a lot of that.

In a study where researchers compared the milk of people on a Western diet and people on a Nonwestern (Nigerian) diet, what was the difference?

People on a Nonwestern (Nigerian) diet had more LCFAs in their milk.

Why did people on a Nonwestern (Nigerian) diet have more LCFAs in their milk in that study?

In the study, it looked at Nigerian women that lived on the coast. They consumed a lot more fish, so more LCFA.

Is the link between the consumption of fish and LCFA in the milk only exclusive to humans?

No, this also happens in other monogastrics as well, like dogs for example.

What are the 2 FAs in goat milk that give it it's unique flavor (which some people don't like)?

Caproic Acid

Caprylic Acid

Milk Fat is synthesized by what 2 pathways?

De Novo Synthesis in MECs.

Breakdown of blood triglycerides (from either diet or fat stores) and re-synthesis in MECs.

Each of the 2 pathways of milk fat synthesis contributes to approximately what percentage of milk fat?

Each contributes approximately 50% of milk fat.

The capillary delivers what 4 things to the mammary gland epithelial cells?

NEFA

Triglycerides

Glucose

Glycerol

What does NEFA stand for?

Non-Esterified Fatty Acids

Where did Non-Esterified Fatty Acids (NEFAs) come from?

They are from the adipose tissue stores and released in the blood.

In the blood, Non-Esterified Fatty Acids (NEFAs) are bound to what carrier protein?

albumin

When NEFAs go from blood to the ECF around the epithelial cells, what is it providing?

Free Fatty Acids

How are Triglycerides transported in the blood to the mammary gland? (2)

via Chylomicrons and Lipoproteins (VLDL, IDL, LDL, HDL)

Chylomicrons deliver ___-___% of Triglycerides to the epithelial cells.

80-95%

VLDL deliver ___-___% of Triglycerides to the epithelial cells.

45-65%

Can the Triglycerides go directly from the blood to the ECF around the epithelial cells?

No, they have to be broken down.

What is the enzyme that acts on lipoproteins to cut the FAs from the glycerol backbone?

Lipoprotein Lipase (LPL)

Lipoprotein Lipase (LPL) hydrolyzes Triglycerides into what 4 products to diffuse into the ECF?

Monoglycerides

Diglycerides

Free Fatty Acids

Glycerol

Is Glucose broken down before going from blood to the ECF around epithelial cells?

No

Compare the differences in [glucose] in the circulation of monogastrics and ruminants. (general)

[Glucose] in the blood of monogastrics is high.

Ruminants have very low circulating [glucose].

Is Glycerol broken down before going from blood to the ECF around epithelial cells?

No