The Biochemistry of Milk

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The Biochemistry of Milk

• Ch. 23

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• How do you milk a cow?
• Video
• http//www.moomilk.com/faq.htmTo20make

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The Complex Nature of Milk

• Milk supplies the calcium for building bones and
  teeth, especially during adolescence
• Milk is 87 water
• However thats a solvent for over 250 chemical
  compounds, milk sugar (what is the name for milk
  sugar_____?____) water-soluble vitamins and trace
  minerals and salts

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Protein

• Two main proteins make up milk
• 80 Casein milk protein
• 20 Whey milk protein
• Micelles an aggregation or cluster, of
  molecules, often found in colloidal dispersions
• The light reflecting from micelles makes milk
  white
• As long as milk keeps its normal acidity level,
  about pH 6.6, casein remains stable

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Protein Continued

• When the pH level decreases the milk forms lumps
  or coagulates.
• Curds The casein clumps that separate from the
  liquid when milk coagulates
• When cooking with milk you can prevent curdling
  by using starch to thicken the milk
• If you want to coagulate milk, you can use the
  enzyme rennin or vinegar.
• Whey protein found in the liquid that remains
  after fat and casein have been removed from milk.
  
• Whey is also called serum protein

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Fats

• Milk is an emulsion because small globules of fat
  (lipid) are dispersed throughout the water
• Creaming process in which some of the fat
  droplets come together in larger clusters that
  rise and float to the top of the milk
• These clusters rise to the surface because fat is
  less dense than the watery portion of milk
• Cream simply milk that is extra rich in
  emulsified fat droplets
• The fat in cows milk are most complex lipids,
  over 400 different fatty acids
• Click For Milk Experiment

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Carbohydrate

• Lactose or milk sugar is the main carbohydrate
• Lactose provides food energy
• Also adds body to milk as well as a sweet flavor
• When milk is heated, lactose reacts with amino
  acids in the protein (giving cooked milk a
  slightly caramel flavor)
• When you consume milk, lactose becomes available
  to the body because of the enzyme lactase.
• This enzyme breaks lactose down into galactose
  and glucose, which is used in the body for
  fermentation during digestion.

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Carbohydrate Continued

• Do you know someone who cannot drink milk???
• People can be lactose intolerance the inability
  to digest milk due to the absence of the enzyme
  lactase in the intestines
• People who are lactose intolerant cannot break
  down lactose in their body. When they drink the
  milk they can have bloating, stomach cramps and
  diarrhea.!!! -NOT FUN

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Minerals and Vitamins

• Milk has salt that occurs naturally
• Salts in milk include chlorides and phosphates
  (in very low amounts)
• Salt in milk helps prevent curdling
• If an acid is added to milk (what would be an
  example of an acid), the pH lowers which removes
  the calcium ions from the casein, making the milk
  curdle forming _____and _______
• Four vitamins found naturally in milk, riboflavin
  is found in the largest quantity.
• Breaks down when exposed to light

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Pasteurization

• Shelf Life time a food product can be stored
  before deteriorating.
• When pasteurizing milk, its heated to high
  temperatures for a short time to destroy harmful
  bacteria
• Pasteurization denatures enzymes that cause milk
  to spoil
• Pasteurization has a small effect on milks
  nutritional value, creating a slight loss of
  thiamin, vitamin B12, vitamin C
• DO YOU THIN THAT DRINKING UNPASTURIZED MILK IS
  BETTER FOR YOU?

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Homogenization

• Under pressure of 2,000 to 2,500 pounds per
  square inch, milk is forced through small
  openings in a machine called a homogenizer
• The fat particles break down, an emulsifier
  surrounds the fat particle, which keeps the
  particles permanently separated
• As a result the milk you buy does not have cream
  on the top.

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Fortification

• Fortification the addition of a nutrient to a
  food
• Ex. What nutrient is milk fortified with___?___
• Without vitamin D, your body cant absorb calcium
  and phosphorus very well.
• To fortify milk with vitamin D, it may be exposed
  to ultraviolet light, which convert some of the
  milk fat components to vitamin d

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Fluid Milk/ Ultrahigh-Temperature Milk (UHT)

• Fluid milk is categorized by fat content
• Whole milk 8g fat
• Reduce-fat milk (2) 5g fat
• Low-fat milk (1) - 2.5g fat
• Fat-free milk trace fat
• Ultrahigh-Temperature Milk (UHT)
• With special processing milk can be stored
  without refrigeration for three months
• This is called UHT because its prepared by
  heating for a short time at ultrahigh
  temperatures.
• Placed in special sealed packages
• Flavor improves over time

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Concentrated Milk

• Evaporated milk is whole milk that has been
  heated at low pressures, causing up to 60 if the
  water present to evaporate at temperatures well
  below milks normal boiling point.
• Carrageenin a vegetable gum, is often added to
  evaporated milk before processing to stabilize
  the casein proteins
• Sweetened condensed milk canned product in
  which 50 of the water has been removed and sugar
  added.
• Sweetened condensed milk is 44 sugar

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Cream/Dry Milk

• Half-and-half is 10.5-18 fat
• Light cream 18-30 fat
• Light whipping cream 30-36 fat
• Heavy whipping cream contains at least 36 fat
• Dry Milk water is removed, leaving a dry solid
  material
• Milk Solids proteins, carbohydrates, fat,
  minerals, and vitamins that were dissolved in the
  liquid portion of the milk
• Nonfat milk has a longer shelf life because it
  has the least amount of fat (used for baking an
  enriching products)

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Cultured Milk Products

• Culture controlled bacterial population that
  is added to milk
• The starter bacteria produce acid and flavors
  that are characteristic of each fermented milk
  product.
• Commercial producers use lactic-acid bacteria to
  break down lactose
• Inoculation adding the starter culture to milk
  during the fermentation process that produces
  different cultured milk products
• Incubation period time needed for bacteria to
  grow and ferment the milk during the process of
  culturing milk to make various products finally
  its cooled down to stop or slow bacterial growth
• What are some examples of cultured foods???

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Buttermilk/Sour Cream/Yogurt

• Buttermilk used to be the fluid left over from
  producing butter, today its a cultured product
  prepared from low-fat milk
• Sour Cream culture of streptococcus lactis is
  added to cream.
• Yogurt eastern European food, yogurt contains
  lactose, lactic acid, B vitamins and high
  concentrations of protein
• Yogurt is prepared by adding a bacterial culture
  to milk that has been heated
• Bacteria used to making yogurt must be incubated
  between 41C-45C for around 8 hours

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Cheese

• Cheese is made by coagulating the casein protein
  in milk.
• Once the curds have formed, the whey is drained
  away. (heating and cutting the whey helps this
  drain)
• The curd is then treated and allowed to ripen
• During ripening, the cheese is hung for at least
  60 days, some take months
• Four main categories of cheese are based on
  moisture content
• Very hard cheese parmesan and Romano
• Hard cheese cheddar, Colby and provolone
• Semi-Soft cheese Munster, Roquefort, and
  stilton
• Soft cheese brie, camembert, and mozzarella
• Unripened Cheese cottage cheese and cream cheese

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Storing and Cooking with Milk

• How many of you leave milk on your table when
  eating dinner??
• Is that safe?? Even if its for ½ hour?
• Milk retains its quality for 1-3 weeks when
  properly stored
• Extra credit for someone who can tell me the
  correct temperature
• Remember riboflavin is sensitive to light
• Would whole milk or low fat milk spoil faster or
  would they spoil at the same time?

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Making Foams

• Several factors affect the ability of cream to
  make a foam.
• Fat content higher the fat level, the better
  the foam
• Temperature cold temperature increase the
  viscosity , including the beaters and bowl
• Amount of cream whipping small amounts of cream
  usually gives better results than whipping large
  amounts
• Sugar content adding sugar decreases both the
  volume and stiffness of the foam, its best to add
  sugar after the cream has reached the desired
  consistency

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Heating Milk

• Milk is sensitive and highly reactive to heat
• Heat denatures and coagulates the whey proteins
  of fresh milk, causing them to precipitate
• Precipitate to cause a solid substance to
  separate from a solution
• To prevent milk from scorching put milk in a
  double boiler or heat over VERY LOW TEMPERATURE
• What happens to milk when you heat milk in a
  sauce pan that is not stirred?!??
• Skin develops, if you try to remove the skin it
  will regenerate and you lose milk solids
• What is curdling and how does it happen

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Questions

1. How does casein react to acids?
2. How are casein and why alike and different?
3. What makes milk a solution, a colloidal
   dispersion, and an emulsion?
4. Why is lactose a valuable nutrient in milk?
5. How do salts prevent milk from curdling?
6. How is milk processed? What is the purpose of
   each type of processing?

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Questions Continued

1. What does the phrase whole milk mean? How does
   whole milk compare to other classifications of
   milk?
2. What is the difference between sweetened
   condensed milk and evaporated milk?
3. How are cultured milk products made?
4. Explain what ripening is and why its needed to
   make cheese.
5. To make a cream foam, would you get better
   results by using light or heavy whipping cream?
   WHY?
6. What might happen if you leave an open pan of
   milk over high heat without stirring?