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MILK COMPOSITION: PROTEINS

MILK COMPOSITION: PROTEINS. Leo Timms Iowa State University. MILK PROTEINS. Synthesized in the mammary gland from blood amino acids ( except serum albumin and most immunoglobulins ) CASEIN : major class of milk proteins whey proteins non protein nitrogen / others

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MILK COMPOSITION: PROTEINS

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  1. MILK COMPOSITION:PROTEINS Leo Timms Iowa State University

  2. MILK PROTEINS • Synthesized in the mammary gland from blood amino acids ( except serum albumin and most immunoglobulins) • CASEIN: major class of milk proteins • whey proteins • non protein nitrogen / others • Species variation: 1% (primates) - >15% • Limited variation within species/ animal

  3. Protein Composition* Protein cow human sow Total % 3.2-4.2 .88-1 6 Casein % 79 35 58 Whey protein % 21 65 42 Alpha-lactalbumin 3.5 17 15 Beta lactoglobulin 9 0 2 Lactoferrin <1 17 1 Immunoglobulin 3 11 7 Serum albumin 1 6 2

  4. CASEINS • Major milk proteins (~ 80%) • Excellent amino acid composition • Highly digestible • Secreted as a micelle (colloid + P + Ca) • Acid precipitation at pH 4.6 • (normal milk pH 6.6-6.9) • Micelle hydrolyzed by rennin (curd) • Variants: alpha, beta, gamma, kappa

  5. CASEINS * Casein alpha beta gamma kappa grams/ liter 13.7 6.2 1.2 3.7 phos. (P) % 1.05 .6 .15 .3 mol. wt. 24K 24K 20K 19K Pi/ molecule 8-10 5 1 1 Carbohydrate % 5

  6. NON - CASEIN PROTEINS Protein function Conc. mg/l alpha lactalbumin lactose syn. 700 beta - lactoglobulin* ??? 3000 albumin ** like blood 300 Immunoglobulin ** immune prot. 600? Lactoferrin iron binding 18 Ceruloplasmin Cu carrier low Protein hormones Prl / PL ~(blood) Other enzymes / growth factors/ etc. low * not in humans ** mainly blood derived

  7. NON - PROTEIN NITROGEN Compoundmg / l Total protein 30,000 Total NPN ~ 300 Urea - N ** ~ 150 ** Mimics blood urea - excellent diagnostic tool esp. for ruminants

  8. Fraction % of protein as-1 - Casein 34-40 as-2 - Casein 11-15 b - Casein 25-35 k - Casein 8-15 b - Lactoglobulin 7-12 a - Lactalbumin 2-4 Blood serum albumin .5-2 Lactotransferrin trace Immunoglobulins trace The value of milk protein Nomenclature and relative amounts

  9. AMINO ACIDS • What do the blood amino acids look like that get to the mammary gland? • diet = mammary gland (non-ruminants) • diet is different than mammary gland in ruminants • Rumen degradeable protein - Ammonia - bacterial protein (CHO) or blood urea • Rumen by-pass protein/AA = mammary gland!

  10. LIPIDS OR FATS

  11. AMINO ACID (nutrient)UPTAKE • Arterial concentration of amino acids • Rate of mammary blood flow • Extraction rate of amino acids by gland • Measure venous concentration of AA • ** Arterio venous difference (AVD) *** AVD X blood flow rate = total nutrient extracted

  12. AMINO ACID (nutrient)UPTAKE

  13. PROTEIN SYNTHESIS • DNA transcription • RNA messenger ribosomal transfer translation • PROTEINS

  14. PROTEIN SYNTHESIS ATP AMP + P + P

  15. PROTEIN SYNTHESIS Attach + move AA on chain 2 GTP 2 GDP + 2 P

  16. PROTEIN SYNTHESIS GOLGI APPARATUS casein + ATP casein-P + ADP (casein kinase) Assembled into micelles Casein-P + Ca 140 nanometers secretory vesicles

  17. CASEIN MICELLES 90% of Ca in micelle

  18. MILK COMPOSITION Casein micelles Apical membrane Basement membrane

  19. The value of milk protein Amino acids • 20 possible amino acids – Connected via peptide bond to form protein + + + + + • Casein is a phospho protein (phosphorus is linked to a serine amino acid) P P P

  20. Casein micelle structure – calcium phosphate interactions • Casein phosphate centers act as nucleation sights and several peptide chains inhibit the growth of calcium phosphate microgranules • Proposed that 66 calcium and 66 phosphates (1/3 organic) ions along with water form calcium phosphate microgranules Adapted from Heat Induced Changes in Milk – 1995 Holt 105-133

  21. Casein micelle structure – proposed model • 10,000 polypeptide chains of the four caseins • micro-granules of calcium phosphate • glyco-macro peptide portion on k-casein is concentrated on the surface • rennet coagulation - remove hairs Adapted from Adv. Prot. Chem – 1992, Holt 43:63-151

  22. The value of milk protein Casein vs whey protein

  23. The value of milk protein Casein vs whey protein • Separated during cheese making

  24. Cheese Structure – at set Adapted from Kiely et al 1992 • The protein matrix contains embedded fat and moisture • Protein matrix is cross-linked by calcium and phosphate

  25. Cutting and removal of whey: 10 lbs milk 1 lb cheese 9 lb whey

  26. The value of milk protein Milk components • Protein is considered to be the most valuable • World demand for dairy protein currently exceeds the world supply – will continue for the next decade

  27. Fractionation of milk protein Whey utilization 1970 Today

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