Department of Food Science and Nutrition Intro to Milk
Chemistry and How Product Quality is Affected by Handling Tonya C.
Schoenfuss
Slide 2
Objective Overview of milk components & differences between
species Major factors affecting on milk quality Somatic Cell Count
Microbial Count Handling
Slide 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 1919 1959 dairy product professors
left and formed the Dairy Industry Department
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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
Slide 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).
http://www.biology-online.org/dictionary/Mammalia
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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
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Commercial Milk Producing Mammals Cows Goats Sheep Water
buffalo Yak Camels Horses Ruminants Have a 4 compartment stomach
for fermentation and digestion of food
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Goats Toggenberg La Mancha (from the US) Oberhasli Saanen
Alpine Nubian The Best Breed (according to Tonya)
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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!
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Others Reproduction Goats and Sheep are seasonal breeders Cow
gestation 9 mos Goat & Sheep about 5 mos
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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Health of Udder Infections (mastitis) in udder Affect milk
quality Affect milk safety Affect your ability to sell the
milk
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
Slide 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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Chen et al.Journal of Dairy Science Vol. 93 No. 4, 2010 Cheese
made from milk with higher somatic cell count had lower sensory
scores
Slide 23
Milk Quality Is Affected by Bacterial Count Spoilage / End of
Shelf Life Numbers/ ml or Gm Time (Days) Pasteurization
sterilization Higher counts, higher quantity survive Greater enzyme
load
Slide 24
Milk Quality at the U of MN http://qualitycounts.umn.edu
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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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Mastitis Screening California Mastitis Test (CMT) Wisconsin
Mastitis Test (WMT) Direct Microscopic Somatic Cell Count (DMSCC)
Coulter Counter or flow cytometer
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
Slide 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
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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
Slide 36
Fat Synthesis Fat profile influenced by: type of ruminant stage
of lactation Diet Breed Rumen microflora Rumen pH Season
Slide 37
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
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Fatty Acids in Milk (notice the wide range of melting points)
Fatty AcidNumber of CarbonsMelting Point (C)Average Range
Nomenclature (C:Double bonds)g/100g Saturated: Butyric4:0-82 - 5
Caproic6:0-41 - 5 Caprylic8:0161 - 3 Capric10:0312 - 4
Lauric12:0442 - 5 Myristic14:0548 - 14 Palmitic16:06322 - 35
Stearic18:0709 - 14 Mono-unsaturated: Palmitoleic16:11 - 3
Oleic18:11620 - 30 Diene: Linoleic18:2-51 - 3 Polyene:
-Linolenic18:3-120.5 - 2
Slide 39
C. Lopez / Current Opinion in Colloid & Interface Science
16 (2011) 391404 Fatty acid Composition from Various Species
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Goat milk fat easier to hydrolyze by digestive lipases
International Dairy Journal 35 (2014) 153e156
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Diet Can Change Nutrition Cows fed corn silage (A) or corn
silage + Linseed (B) Increase in unsat. fatty acids in feed led to
increase in milk Note the trans-fat AB Lopez, et.al. 2008. J.
Agric. Food Chem. 56:5226-5236
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Fatty acids are linked to a glycerol backbone Glycerol Oleic
acid C Palmitic acid Lipid Basics mono, di and triglycerides C
C
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1,3-Dioleoyl-2-palmitoylglycerol 3 water molecules removed =
condensation reaction Glycerol Oleic acid Palmitic acid This is a
triglyceride
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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
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Proteases (also called proteinase or peptidase) Enzymes that
hydrolyze the peptide bonds in proteins Schematic of a
Tripeptide
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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
Slide 47
Enzymatic Protein Hydrolysis
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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
Slide 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