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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. - PowerPoint PPT Presentation
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MILK COMPOSITION:LIPIDS OR FATS
Leo TimmsIowa State University
Why is fat important? Concentrated source of energy
2.25x as much E as glucose Provide insulation
Maintain body temperatureProtect vital organs
Membrane synthesis Vitamin transport
MANY MORE!!!
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
LIPIDS OR FATS . Wt % of lipids .Lipid Cow Human RatTriglyceride 97-98 98.2 87.5
Diglyceride .25-.48 .7 2.9Monoglyceride .02-.04 T 0.4Free fatty acids .1-.4 .4 3.1Phospholipids .6 – 1 .25 0.7Cholesterol .2 - .4 .25 1.6
Triglyceride
Glycerol + 3 Fatty Acids Triglyceride
Connected by an ester bond
Fatty acids can be the same or mixed
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
LIPIDS OR FATS
LIPIDS OR FATSWhere do milkfat precursors come from?
1. Blood lipids: long chains• diet and adipose tissue
• lipoproteins (liver)• chylomicrons (gut)
• free fatty acids / ketones2. Glucose: glycerol
fatty acids (non ruminants)3. Acetate and butyrate (ruminants)
LIPIDS OR FATS
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
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!
LIPIDS OR FATS
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.)
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
Free fatty acids
MILK FATTY ACIDS - COW
% from de novo % from VLDLFatty 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
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
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
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
MILK FATTY ACIDSC4:0 Butyric acid C16:0 Palmitic acidC6:0 Hexanoic C18:0 StearicC8:0 Caprylic C18:1 OleicC10:0 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
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)
MILK COMPOSITIONApical membrane
Basementmembrane