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% cows) 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 P i / molecule 8-10 5 1 1 Carbohydrate % 5

6. WHEY PROTEINS (non-casein) 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 Compound mg / l Total protein 30,000 Total NPN ~ 300 Urea - N ** ~ 150 ** Mimics blood urea - excellent diagnostic tool esp. for ruminants

8. Nomenclature and relative amounts traceImmunoglobulins traceLactotransferrin.5-2Blood serum albumin 2-4  - Lactalbumin 7-12  - Lactoglobulin 8-15  - Casein 25-35  - Casein 11-15  s-2 - Casein 34-40  s-1 - Casein % of proteinFraction The value of milk protein

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 Apical membrane Basement membrane Casein micelles

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

20.  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 Casein micelle structure – calcium phosphate interactions Adapted from Heat Induced Changes in Milk – 1995 Holt 105-133

21.  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 Casein micelle structure – proposed model 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. Adapted from Kiely et al 1992 Cheese Structure – at set  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 WaterLactoseFatProteinMinerals Whole Milk87.6%4.8%3.7%3.2%.70% Whole Milk (dry basis) ---38.7%29.8%25.8%5.6% Skim Milk90.9%4.98%.05%3.32%.73% Skim Milk (dry basis) ---54.8%.55%36.6%8.0%

27. Whey utilization Fractionation of milk protein 1970Today