MILK COMPOSITION: LIPIDS OR FATS

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MILK COMPOSITIONLIPIDS OR FATS

• Leo Timms
• Iowa State University

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Why is fat important?

• Concentrated source of energy
• 2.25x as much E as glucose
• Provide insulation
• Maintain body temperature
• Protect vital organs
• Membrane synthesis
• Vitamin transport
• MANY MORE!!!

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MILK COMPOSITION
LIPIDS OR FATS

• Mostly triglycerides
• most variable component!!!
• - across and within species!
• lt1 - gt50 fat species differences
• variability in fatty acid profiles (handout)
• Fatty acid content is labile diet changes
• major TASTE component in milk

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LIPIDS OR FATS
. Wt of
lipids . Lipid Cow
Human Rat Triglyceride 97-98
98.2 87.5 Diglyceride .25-.48
.7 2.9 Monoglyceride .02-.04
T 0.4 Free fatty acids .1-.4
.4 3.1 Phospholipids .6
1 .25 0.7 Cholesterol
.2 - .4 .25 1.6

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Triglyceride
Glycerol 3 Fatty Acids Triglyceride Connected
by an ester bond Fatty acids can be the same or
mixed
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FATTY ACIDS

• Long chain gt C14 (14 carbons)
• - diet - adipose
• Medium chain C10-C14 (10-14 carbons)
• Short chain lt C8 (lt 8 carbons)
• made in the mammary gland
• - glucose (NR) - acetate/butyrate (rum)
• Saturated no double bonds
• Unsaturated double bonds

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LIPIDS OR FATS
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LIPIDS OR FATS
Where do milkfat precursors come from?

• 1. Blood lipids long chains
• diet and adipose tissue
• lipoproteins (liver)
• chylomicrons (gut)
• free fatty acids / ketones
• 2. Glucose glycerol
• fatty acids (non ruminants)
• 3. Acetate and butyrate (ruminants)

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LIPIDS OR FATS
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FATTY ACIDS

• Long chain gt C14 (14 carbons)
• - diet - adipose
• Medium chain C10-C14 (10-14 carbons)
• Short chain lt C8 (lt 8 carbons)
• made in the mammary gland
• - glucose (NR) - acetate/butyrate (rum)
• Saturated no double bonds
• Unsaturated double bonds

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FATTY ACIDS

• What do the fatty acids of triglycerides look
  like that get to the mammary gland?

• long chain fatty acids (diet / adipose)
• diet mammary gland (non-ruminants)
• diet is different than mammary gland in
  ruminants
• Polyunsaturated fatty acids from feeds are
  hydrogenated (saturated) in rumen
• Rumen by pass fats mammary gland!

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LIPIDS OR FATS
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GETTING FATS INTO THE GLAND

• 35-50 of triglycerides (chylomicrons/
  lipoproteins taken up by mammary gland)
• Triglycerides must be broken down to get into
  mammary gland.
• Lipoprotein lipase capillary walls
• 17 -45 of milk fat from acetate
• 8 - 22 of milk fat from butyrate
• Ruminants 50 diet / 50 de novo syn.
• Acetate/ butyrate / ketones in milk (diag.)

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Lipoprotein lipase (LPL)

• Anchored to capillary walls
• Hydrolyses triglycerides
• 1-3 times
• All cells have equal access to free FAs
• Therefore must circulate in blood as
  triglycerides
• Tissues with higher LPL activity can uptake more
  fat from blood

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Free fatty acids
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MILK FATTY ACIDS - COW
from de novo from
VLDL Fatty acid synthesis fatty
acids C4 - C10 100
0 C12 80 - 90
10 - 20 C14 30 - 40
60 - 70 C16 20 - 30
70 - 80 C18
0 100
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DE NOVO FATTY ACID SYNTHESIS IN THE MAMMARY GLAND

• Occurs in the cytoplasm!
• Need a few things
• short carbon chains ( acetyl - CoA)
• - acetate and butyrate ( ruminants)
• - glucose (acetate) in non ruminants
• reducing equivalents ( NADPH2)
• proper enzymes
• Acetyl CoA carboxylase / fatty acid synthetase

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DE NOVO FATTY ACID SYNTHESIS IN THE MAMMARY GLAND

• Acetyl CoA (2C) HCO3 ATP
• Malonyl CoA (3C) ADP P H
• (acetyl CoA carboxylase - rate limiting)
• Acetyl ACP (2 C) Malonyl ACP (3C)
• next 4 steps - fatty acid synthetase
• Large single cpmplex of enzymes

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DE NOVO FATTY ACID SYNTHESIS IN THE MAMMARY GLAND

• Acetyl ACP (2 C) Malonyl ACP (3C)
• condensation ACP
  CO
• reduction
  NADPH - NADP
• dehydration
  H2O
• reduction NADPH
  - NADP
• 4 carbon chain (Butyrate)
  

• Add 2 carbons at 1 time C2 C3 C4 CO2
• Lots of energy 1 ATP and 2 NADPH / 2 carbons
• fatty acid chain attached to acyl carrier protein

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MILK FATTY ACIDS
C40 Butyric acid C160 Palmitic acid C60
Hexanoic C180 Stearic C80 Caprylic
C181 Oleic C100 Caproic C182
Lineoleic (ess.!) C120 Auric C183
Linolenic (ess.) C140 Myristic

• Most species lots of palmitate / oleic
• More short chains in ruminants
• Conjugated linoleic acid (CLA)
• Other species diff goats C8 C10

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MILK TRIGLYCERIDE SYNTHESIS

• Occurs at cytoplasmic surface of smooth
  endoplasmic reticulum
• Glycerol fatty acids (esterified)
• Esterases (enzymes)
• Fatty acid specificity to C site
• Fatty acids coalesce to form droplets
• Grow and move to apical membrane
• Secreted with membrane (protein coating)

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MILK COMPOSITION
Apical membrane
Basement membrane