Intro to Milk Chemistry and How Product Quality is Affected by Handling

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1 Intro to Milk Chemistry and How Product Quality is Affected by Handling Tonya C. Schoenfuss Department of Food Science and Nutrition

2 Objective Overview of milk components & differences between species Major factors affecting on milk quality Somatic Cell Count Microbial Count Handling

3 History of Dairy Products at U of MN School of Ag opened in 1888 on the St. Paul campus 1923 Haecker Hall opened as the new Dairy building Eckles arrived in dairy product professors left and formed the Dairy Industry Department

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5 Definition of Milk milk is the lacteal secretion, practically free from colostrum, obtained by the milking of one or more healthy cows, which contains not less than 8.25% solids-not-fat and not less than 3.25% milkfat

6 What Animals Produce Milk? Mammals warm-blooded vertebrate animals belonging to the class mammalia, including all that possess hair and suckle their young. It includes three major groups: placentals and marsupials, and monotremes (echidna and platypus).

7 Milk Domestication of animals Goats 10,000 B.C. in Iran Sheep 9,000 11,000 BC SW Asia Cows 8,000 BC India, Mid East, Sub- Saharan Africa

8 Commercial Milk Producing Mammals Cows Goats Sheep Water buffalo Yak Camels Horses Ruminants Have a 4 compartment stomach for fermentation and digestion of food

9 Goats Toggenberg La Mancha (from the US) Oberhasli Saanen Alpine Nubian The Best Breed (according to Tonya)

10 What Are the Differences? Gross composition (fat/protein) Protein primary structure Fat globule size difficult to remove fat from goat milk Fatty acid composition Flavor!

11 Others Reproduction Goats and Sheep are seasonal breeders Cow gestation 9 mos Goat & Sheep about 5 mos

12 Typical Milk Composition

13 Protein Differences Cow Goat

14 Fat Globule Size Difference Journal of Dairy Science Vol. 83, No. 5, 2000

15 You Need High Quality Raw Milk to make High Quality Dairy Products Factors affecting raw milk quality from the production side: Genetics On-farm sanitation Health of udder Stage of lactation Feed Post-milking treatment and handling

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17 Health of Udder Infections (mastitis) in udder Affect milk quality Affect milk safety Affect your ability to sell the milk

18 Relationship between Log Score, CMT reading, SCC Range, Midpoint and estimated daily milk loss (this is cow data) Log SCC Milk Loss Score CMT SCC Range Midpoint lb/cow/day 0 Neg 0-17K (12,500) 0 1 Neg 18K - 34K (25,000) 0 2 Neg 35K - 70K (50,000) 0 3 Neg 71K - 140K (100,000) Neg 141K - 282K (200,000) 3 5 Trace 282K - 565K (400,000) K - 1,130K (800,000) ,131K - 2,262K (1,600,000) ,263K - 4,525K (3,200,000) ,526K - 9,999K (6,400,000) 10.5 Source: National DHIA & Nelson Philpot 1984

19 SCC in Goats have higher SCC s than cow milk increase greatly with later lactations 1,000,000/ml limit for goats, but exceeded M.J. Paape et al. / Small Ruminant Research 68 (2007)

20 Why is Mastitis Important? Lost milk volume Reduced cheese yield Increased microbial, pathogen and enzyme load (proteases & lipases a concern) Reduced protein quality Off-flavors

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22 Cheese made from milk with higher somatic cell count had lower sensory scores Chen et al.journal of Dairy Science Vol. 93 No. 4, 2010

23 Numbers/ ml or Gm Milk Quality Is Affected by Bacterial Count Spoilage / End of Shelf Life Time (Days) Pasteurization sterilization Higher counts, higher quantity survive Greater enzyme load

24 Milk Quality at the U of MN

25 Milking Techniques Affect SCC & Microbial Count Washing udders, trimming hair Glove use by operators Workers looking for mastitic cows Teat dip Properly operating milking equipment Clean & un-cracked inflations Vacuum pressure Release when done

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28 Mastitis Screening California Mastitis Test (CMT) Wisconsin Mastitis Test (WMT) Direct Microscopic Somatic Cell Count (DMSCC) Coulter Counter or flow cytometer

29 D100.Hhttp:// o/dairy/d100.htmtm

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33 Lipid Basics Lipids include: Acylglycerols (mono, di & triglycerides) Neutral lipids Sterols Vitamins Carotenoids Phospholipids Polar lipids Purpose: Energy storage Structural components of cell membranes Signaling molecules

34 Fat is surrounded by a membrane in milk If the membrane is damaged, native lipases can attack the triglycerides to release free fatty acids This makes milk rancid

35 Flavor Fat can be a source of potent flavors in dairy products: Short-chain free-fatty acids (as the result of lipase hydrolysis of the triglycerides) contribute Soapy, goaty, rancid, vomitty, Methyl ketones blue-cheese flavors, diacetyl Aldehydes from oxidation products Lactones produced during heating triglycerides from c6 c16 hydroxy acids. Tend to be fruity flavors Branched chain fatty acids generated by cultures

36 Fat Synthesis Fat profile influenced by: type of ruminant stage of lactation Diet Breed Rumen microflora Rumen ph Season

37 Fat Synthesis C16 C18 fatty acids derived from blood (Come from what the animal eats) Shorter chained fa s are formed in secretory cell So, pasture feeding changes what is in the milk

38 Fatty Acids in Milk (notice the wide range of melting points) Fatty Acid Number of Carbons Melting Point ( C) Average Range Saturated: Nomenclature (C:Double bonds) g/100g Butyric 4: Caproic 6: Caprylic 8: Capric 10: Lauric 12: Myristic 14: Palmitic 16: Stearic 18: Mono-unsaturated: Palmitoleic 16:1 1-3 Oleic 18: Diene: Linoleic 18: Polyene: α-linolenic 18:

39 Fatty acid Composition from Various Species C. Lopez / Current Opinion in Colloid & Interface Science 16 (2011)

40 Goat milk fat easier to hydrolyze by digestive lipases International Dairy Journal 35 (2014) 153e156

41 Diet Can Change Nutrition Cows fed corn silage (A) or corn silage + Linseed (B) A B Lopez, et.al J. Agric. Food Chem. 56: Increase in unsat. fatty acids in feed led to increase in milk Note the trans-fat

42 Lipid Basics mono, di and triglycerides Fatty acids are linked to a glycerol backbone C C C Oleic acid Palmitic acid Glycerol Oleic acid

43 1,3-Dioleoyl-2-palmitoylglycerol Oleic acid Palmitic acid Oleic acid 3 water molecules removed = condensation reaction Glycerol This is a triglyceride

44 Milk Becomes Rancid if Mishandled because of lipases Careful handling of milk prior to pasteurization is key do not want to damage the fat globule membrane How? Freezing raw milk Leaky pumps that introduce air Excessive pumping or bulk tank agitation Time until pasteurization Temperature (colder, slower reaction rate) Individual cows can produce spontaneously rancid milk

45 Proteases (also called proteinase or peptidase) Enzymes that hydrolyze the peptide bonds in proteins Schematic of a Tripeptide Peptide bonds H + NH 2 C O C N R 2 C C H N C O C _ O H O R 1 R 3

46 Proteases Proteases come from: milk itself (levels increase with mastitis) microorganisms (added or contaminants) added enzymes (rennet is a protease) If casein is hydrolyzed before cheese making, you will lose more protein to the whey (lose yield) Can get bitter off-flavors in milk from proteases

47 Enzymatic Protein Hydrolysis H 3 N+ GLY ALA LYS THE SER MET PHE ALA Exopeptidase (aminopeptidase) LEU Endopeptidase TRP PHE CYS S-S CYS GLY ILE PHE LEU LEU TRY ALA ARG LYS THE ILE Exopeptidase (carboxypeptidase) +NH 3 COO - ASN -OOC SER ASP VAL HIS GLU PRO

48 Diet can Change Flavor (as can odors in the environment) J. Lejonklev et al J. Dairy Sci. 96 : /jds

49 Diet Can Also Affect Microorganisms in Milk Silage is a large source of spore-forming microorganisms that survive pasteurization Big problem for milk shelf-life, cheese defects and food safety Animal poops the spores, wind up on the teat, get in the milk

50 Thank You!