Intro to Milk Chemistry and How Product Quality is Affected by Handling Tonya C. Schoenfuss Department of Food Science and Nutrition Objective Overview of milk components & differences between species Major factors affecting on milk quality Somatic Cell Count Microbial Count
Handling 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 1919 1959 dairy product professors left and formed the Dairy Industry Department 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 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).
http://www.biology-online.org/dictionary/Mammalia 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, SubSaharan Africa Commercial Milk Producing Mammals
Cows Goats Sheep Water buffalo Yak Camels Horses Ruminants Have a 4 compartment
stomach for fermentation and digestion of food Goats Toggenberg Saanen La Mancha (from the US) Alpine
Oberhasli Nubian The Best Breed (according to Tonya) 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! Others
Reproduction Goats and Sheep are seasonal breeders Cow gestation 9 mos Goat & Sheep about 5 mos Typical Milk Composition Protein Differences Cow Goat Fat Globule Size Difference
Journal of Dairy Science Vol. 83, No. 5, 2000 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 Health of Udder
Infections (mastitis) in udder Affect milk quality Affect milk safety Affect your ability to sell the milk 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
Source: National DHIA & Nelson Philpot 1984 lb/cow/day SCC in Goats have higher SCCs 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) 114 125 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
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 Milk Quality Is Affected by Bacterial Count Numbers/ ml or Gm
Spoilage / End of Shelf Life Time (Days) Pasteurization sterilization Higher counts, higher quantity survive Greater enzyme load
Milk Quality at the U of MN http://qualitycounts.umn.edu 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 Mastitis Screening California Mastitis Test (CMT) Wisconsin Mastitis Test (WMT) Direct Microscopic Somatic Cell Count (DMSCC) Coulter Counter or flow cytometer
Purpose: Energy storage Structural components of cell membranes Signaling molecules 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 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
Fat Synthesis Fat profile influenced by: type of ruminant stage of lactation Diet Breed Rumen microflora Rumen pH Season
Fat Synthesis C16 C18 fatty acids derived from blood (Come from what the animal eats) Shorter chained fas are formed in secretory cell So, pasture feeding changes what is in the milk Fatty Acids in Milk (notice the wide range of melting points) Fatty Acid
Number of Carbons Melting Point (C) Nomenclature (C:Double bonds) Average Range g/100g Saturated: Butyric 4:0
-12 0.5 - 2 Diene: Linoleic Polyene: -Linolenic Fatty acid Composition from Various Species C. Lopez / Current Opinion in Colloid & Interface Science 16 (2011) 391404
Goat milk fat easier to hydrolyze by digestive lipases International Dairy Journal 35 (2014) 153e156 Diet Can Change Nutrition Cows fed corn silage (A) or corn silage + Linseed (B) A B
Lopez, et.al. 2008. J. Agric. Food Chem. 56:5226-5236 Increase in unsat. fatty acids in feed led to increase in milk Note the trans-fat Lipid Basics mono, di and triglycerides Fatty acids are linked to a glycerol backbone O HO
OH C OH C (Z) O HO C
O OH Glycerol Oleic acid Palmitic acid (Z) HO Oleic acid
1,3-Dioleoyl-2-palmitoylglycerol Oleic acid O O O Palmitic acid O Oleic acid
O O Glycerol This is a triglyceride 3 water molecules removed = condensation reaction 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
Proteases (also called proteinase or peptidase) Enzymes that hydrolyze the peptide bonds in proteins Schematic of a Tripeptide Peptide bonds R2 O H + NH2
C C C N H R1 C O H
O N C C R3 O _ 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 Enzymatic Protein Hydrolysis H3N+
GLY ALA LYS THE SER MET PHE
Endopeptidase Exopeptidase (aminopeptidase) CYS S-S LEU TRP PHE
CYS GLY ILE PHE LEU TRY LEU ALA ARG
Exopeptidase (carboxypeptidase) -OOC SER ASP LYS +NH3 ASN
COOVAL HIS GLU IL E THE PRO Diet can Change Flavor (as can odors in the
environment) J. Lejonklev et al. 2013. J. Dairy Sci. 96 :42354241 http://dx.doi.org/ 10.3168/jds.2012-6502 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
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