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! 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. 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

5. Triglyceride Glycerol + 3 Fatty AcidsTriglyceride 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. 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 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

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) + HCO 3 + 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

21. DE NOVO FATTY ACID SYNTHESIS IN THE MAMMARY GLAND Acetyl ACP (2 C) + Malonyl ACP (3C) condensation ACP + CO reduction NADPH - NADP dehydration H 2 O 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

22. 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

23. 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)

24. MILK COMPOSITION Apical membrane Basement membrane