1. Dr. Hurley’s Magical Milk Show
IAVAT STUDENT BRANCH
Dr. Hurley’s Magical Milk Show
Walter Hurley
Professor
Animal Sciences
Crystal Allen
PhD Student
Animal Sciences

2. The Main Milk Components
Water
Lactose
Lipid
Proteins
Minerals
Vitamins
Others
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3. Each component can be viewed as to its :
Biochemical & physicochemical properties
Mechanisms of component synthesis
Importance to the nursing young
Importance as a food source for humans
Factors that affect component variability
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4. Milk is suppose to be easily digested – perishable
For the pig, the milk is usually no more than an hour and a half old from synthesis to digestion:
Gland is emptied by piglet, starts refilling with milk (milk synthesis & secretion)
Milk accumulates in the gland for ~45 min (suckling interval)
Milk is ingested by piglet, ~15-20 seconds (milk ejection)
Milk digested by piglets stomach and intestine
Piglet suckles again 45 min later
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5. Dr. Hurley’s Magical Milk Show
IAVAT STUDENT BRANCH
Dr. Hurley’s Magical Milk Show
These experiments will demonstrate:
Milk phases.
Preparation of butter from cream.
Precipitation of milk protein with acid.
Enzymatic hydrolysis of milk protein.
You will conduct a series of experiments with milk that demonstrate the various fractions and phases of milk.

6. Physicochemical Properties of Milk
Milk is:
an emulsion of fat globules floating in the plasma phase of milk (skim milk),
which in turn is a suspension of casein micelles suspended in the milk serum phase (whey),
which in turn is composed of all the water soluble components (lactose, whey proteins, etc)
Milk viewed through a microscope
Lower magnification
Higher magnification
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7. IAVAT STUDENT BRANCH Cream Skim Milk fat, some protein
Experiment A: Observe and compare thickness of the cream layer in the large tubes. What is the composition of each layer?
Cream
Milk fat, some protein
Skim
Proteins, lactose, water
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8. IAVAT STUDENT BRANCH Processing of milk from the store: Skim Raw Milk
Cool
to 4 C
Cream
40% fat
Centrifuge
60 C
Cream
12% fat
Skim
Homogenize
Standardized milk
Pasteurize
Packaging
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9. IAVAT STUDENT BRANCH Pasteurization:
Ensures safety and enhances shelf life of the milk.
Time & Temperature
“low” pasteurization: 15 seconds at 72 C
or 15 sec at 75 C for homogenized milk
“high” pasteurization: 15 sec at 85 C
“ultra-high temp” [UHT milk]: 2 sec at 140 C or 3 sec at 135 C
Consequences of pasteurization:
Kills bacteria
Inactivates some enzymes (from bacteria or from the milk)
IAVAT STUDENT BRANCH

10. IAVAT STUDENT BRANCH Homogenization:
Prevents the formation of cream layer in stored milk.
High pressure forces liquid through a narrow opening
Fat globules are deformed and disrupted
Must be proper ratio of fat and milk protein so that the protein covers the surface of the smaller droplets so that they will not re-form larger droplets
IAVAT STUDENT BRANCH

11. Experiment B: Butter from cream
Observe consistency of cream in the container cream.
Vigorously shake the container until butter is formed.
Observe consistency of the butter compared with that for cream (step 1).
What is the consistency of the cream initially and after butter is formed. What happened to the milk components for the butter to form?
Butter
Butter “milk”
IAVAT STUDENT BRANCH

12. Physicochemical Properties of Milk
Milk is:
an emulsion of fat globules floating in the plasma phase of milk (skim milk),
which in turn is a suspension of casein micelles suspended in the milk serum phase (whey),
which in turn is composed of all the water soluble components (lactose, whey proteins, etc)
Milk viewed through a microscope
Lower magnification
Higher magnification
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13. Milk Composition Breed Variability
Milk fat concentration varies among the breeds of dairy cattle
lowest % fat - Holstein
highest % fat - Jersey and Guernsey
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14. IAVAT STUDENT BRANCH Species Variability
Cream Cheese =
44% fat, 6% protein, 45% water
Fat percentage is the most variable component among species.
Fat %
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15. Experiment C: Precipitation of casein with acid
Swirl the milk in the flask marked Skim and note the consistency of the film of milk that stays on the wall of the flask.
Slowly add an acidic solution drop-wise to flask. Swirl the flask after each drop. Count the drops.
Observe when a precipitate forms (on the sides of the tube).
Allow precipitate to settle.
What are the two layers called that are formed by this process? What milk component is precipitated under these conditions? Why does this component precipitate under these conditions?
Skim
milk
Whey
What are the components of the two layers?
Curds
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16. Experiment D: Enzymatic hydrolysis of milk protein (casein) to form a curd.
Gently shake contents of the tube marked Whole to remix the milk phases.
Dump the contents of one tube marked Whole into the tube marked Rennin, and dump the other tube marked Whole into the tube marked Pepsin.
Seal the tubes with parafilm, mix and hold in your hand to warm.
Observe each tube every few minutes for hardening of the curd. Turn the tubes upside down to determine when the curd has formed.
What is the consistency of each curd? What happened to the milk for the curds to form?
Pepsin
digested
Rennin
digested
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17. scanning EM of casein micelle
Casein is the major protein in cow milk
Total milk protein = 80% casein + 20% whey proteins
Casein is secreted as a micelle (granular) structure
The casein micelle also contains: the casein proteins calcium and phosphorous
PO3-
Ca++
PO3-
Ca++
PO3-
PO3-
Casein protein
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scanning EM of casein micelle

18. IAVAT STUDENT BRANCH Casein micelle
Perhaps >1000 varieties of cheese
Started >8000 years ago
Micelle
structure
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19. IAVAT STUDENT BRANCH Cheese Making
Heating of milk-promotes bacterial growth
Inoculation- buttermilk/yogurt contains bacteria which acidifies (ferments) the milk
Rennin-enzyme digests casein (milk protein), causing coagulation
Curds & Whey-liquid whey separates from coagulated milk
Pressing-gives shape, squeezes out whey
Curing-bacteria acts upon curds, changing flavor and texture of cheese
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