Transcript Food Science - Tanque Verde Unified District

Food Science
The Properties of Milk & How to Make Cheese!
Milk is a Colloid
Milk is a white liquid produced by the
mammary glands of mammals
It is the primary source of nutrition for
young mammals before they are able to
digest other types of food
Though it appears to be a homogeneous
mixture, milk is actually a colloid, a
suspension of emulsified fats and proteins in a
suspension of water and dissolved sugars,
salts and minerals
Because up to 87% of this mixture is water,
light is easily able to pass through milk and
gives it the bright translucent “glow” called
the Tyndall Effect
Milk Macromolecules
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The major proteins in milk are casein, derived
from the Latin caseus, from which the word
“cheese” also originates, and whey
◦ Casein is insoluble and forms “micelles” in aqueous
solution; denatures and coagulates through renneting and
acidification
◦ Whey protein is soluble in aqueous solution; denatures at
high heat
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The major carbohydrate in milk is lactose (a
disaccharide of glucose and galactose), as well as
smaller amounts of other oligosaccharides
The main lipids in milk are butterfat triglycerides
Milk also contains dissolved ions and minerals such
as calcium phosphate, magnesium, sodium, citrate,
as well as dozens of vitamins
The Nature of Denaturation
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When proteins are exposed to a denaturing agent, their 3dimensional structure is affected
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Tertiary structure is “unraveled” into strands of amino
acids (polypeptide chains)
Amino acids retain polarity/nonpolarity and are
spontaneously influenced by presence of water to renature
◦ Leads to tangled clumps of protein called coagulation
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The Process of Making Cheese
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Making cheese involves four steps:
◦ Acidification (dropping pH denatures casein)
 This creates fragile curds (early cheese) that separate
from water
◦ Coagulation (renneting or heating)
 Rennet is an enzyme found in calf stomachs, hydrolyzes
casein and traps fat globules in the formed structure
 Heating (for more delicate cheeses) at 110-120 ⁰C
◦ Dehydration (separating curds from whey)
 Coagulated milk solids are insoluble and are separated
from whey, water, and milk sugars
◦ Salting/Flavoring (removing water via osmosis)
https://www.youtube.com/watch?v=bu4YhxkIgos
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Cheeses are aged weeks or even years,
depending on variety
Acidification via Fermentation
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A simple way of making cheese is to
rely on bacterial cultures that undergo
lactic acid fermentation to drop the
pH in milk
◦ Lactococcus lactis are bacteria that are
used extensively by dairy producers
 Consume the lactose sugars in milk in the
absence of oxygen for the production of ATP
 L. lactis are also used in sour cream, buttermilk,
cottage cheese, kefir, and also cucumber
pickles and sauerkraut
 Arguably the most important bacteria to the
dairy industry
Composition of Cheese
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Because the insoluble milk solids are
separated from the soluble components,
cheese has a high content of
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Protein
Saturated Fats
Cholesterol
Calcium and Sodium
It has a low content of carbohydrates,
which are soluble
Follow-Up Questions
Based on what you’ve learned about
colloids, what would happen if fresh milk
were allowed to sit for a period of time?
 As you cook an egg, the albumin protein
changes from a clear liquid to a solid
white. What is happening?
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