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
Score
0
1
2
3
4
5
6
7
8
9
CMT
Neg
Neg
Neg
Neg
Neg
Trace
1
2
2
3
SCC Range
0 - 17K
18K - 34K
35K - 70K
71K - 140K
141K - 282K
282K - 565K
566K - 1,130K
1,131K - 2,262K
2,263K - 4,525K
4,526K - 9,999K
SCC
Midpoint
(12,500)
(25,000)
(50,000)
(100,000)
(200,000)
(400,000)
(800,000)
(1,600,000)
(3,200,000)
(6,400,000)
 Source: National DHIA & Nelson Philpot 1984
Milk Loss
lb/cow/day
0
0
0
1.5
3
4.5
6
7.5
9
10.5
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) 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
• http://www.infovets.com/demo/demo/dairy/
D100.Hhttp://www.infovets.com/demo/dem
o/dairy/D100.HTMTM
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
• 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 fa’s 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
-8
2-5
Caproic
6:0
-4
1-5
Caprylic
8:0
16
1-3
Capric
10:0
31
2-4
Lauric
12:0
44
2-5
Myristic
14:0
54
8 - 14
Palmitic
16:0
63
22 - 35
Stearic
18:0
70
9 - 14
Mono-unsaturated:
Palmitoleic
16:1
1-3
Oleic
18:1
16
20 - 30
18:2
-5
1-3
18:3
-12
0.5 - 2
Diene:
Linoleic
Polyene:
α-Linolenic
Fatty acid Composition from
Various Species
C. Lopez / Current Opinion in Colloid &
Interface Science 16 (2011) 391–404
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
C
Oleic acid
C
C
Palmitic acid
Glycerol
Oleic acid
1,3-Dioleoyl-2-palmitoylglycerol
Oleic acid
Palmitic acid
Oleic acid
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
C
H
O
N
C
C
H
O
R1
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
A
AL
Endopeptidase
Exopeptidase
(aminopeptidase)
CYS
S-S
LEU
TRP
PHE
CYS
GLY
ILE
PHE
LEU
TRY
LEU
ALA
ARG
Exopeptidase
(carboxypeptidase)
-OOC
SER
ASP
LYS
THE
+NH3
ASN
COOVAL
HIS
GLU
ILE
PRO
Diet can Change Flavor (as can odors in the
environment)
J. Lejonklev et al. 2013. J. Dairy Sci. 96 :4235–4241
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
Thank You!