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MILK COMPOSITION: LIPIDS OR FATS

MILK COMPOSITION: LIPIDS OR FATS. Leo Timms Iowa State University. 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!!!. MILK COMPOSITION.

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MILK COMPOSITION: LIPIDS OR FATS

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  1. MILK COMPOSITION:LIPIDS OR FATS Leo Timms Iowa State University

  2. 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!!!

  3. MILK COMPOSITION LIPIDS OR FATS • Mostly triglycerides • most variable component!!! • - across and within species! • <1% - >50% fat: species differences • variability in fatty acid profiles (handout) • Fatty acid content is labile: diet changes • major TASTE component in milk

  4. LIPIDS OR FATS . Wt % of lipids . LipidCowHumanRat 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

  5. Triglyceride Glycerol + 3 Fatty Acids Triglyceride Connected by an ester bond Fatty acids can be the same or mixed

  6. FATTY ACIDS • Long chain: > C14 (14 carbons) - diet - adipose • Medium chain: C10-C14 (10-14 carbons) • Short chain: < C8 (< 8 carbons) * made in the mammary gland - glucose (NR) - acetate/butyrate (rum) • Saturated: no double bonds • Unsaturated: double bonds

  7. LIPIDS OR FATS

  8. 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)

  9. LIPIDS OR FATS

  10. FATTY ACIDS • Long chain: > C14 (14 carbons) - diet - adipose • Medium chain: C10-C14 (10-14 carbons) • Short chain: < C8 (< 8 carbons) * made in the mammary gland - glucose (NR) - acetate/butyrate (rum) • Saturated: no double bonds • Unsaturated: double bonds

  11. 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!

  12. LIPIDS OR FATS

  13. 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.)

  14. Lipoprotein lipase (LPL) • Anchored to capillary walls • Hydrolyses triglycerides • 1-3 times • All cells have equal access to free FA’s • Therefore must circulate in blood as triglycerides • Tissues with higher LPL activity can uptake more fat from blood

  15. Free fatty acids

  16. MILK FATTY ACIDS - COW % from de novo % from VLDL Fatty acidsynthesisfatty acids C4 - C10 100 0 C12 80 - 90 10 - 20 C14 30 - 40 60 - 70 C16 20 - 30 70 - 80 C18 0 100

  17. 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

  18. 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

  19. 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

  20. MILK FATTY ACIDS C4:0 Butyric acid C16:0 Palmitic acid C6:0 Hexanoic C18:0 Stearic C8:0 Caprylic C18:1 Oleic C10:0 Caproic C18:2 Lineoleic (ess.!*) C12:0 Auric C18:3 Linolenic (ess.) C14:0 Myristic • Most species: lots of palmitate / oleic • More short chains in ruminants • Conjugated linoleic acid (CLA) • Other species diff: goats C8 + C10

  21. 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)

  22. MILK COMPOSITION Apical membrane Basement membrane

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