The Complex Nature of Milk

Name ______Period _____ Days______Date ______

The Biochemistry of Milk

The Complex Nature of Milk

  Vital to health - nutritious

  Versatile for cooking – 87% ______(a solvent for over 250 chemical compounds, the milk sugar lactose, water-soluble vitamins, trace minerals and mineral salts)

  Milk is a ______, a ______, and an ______

Proteins

  80% of milk protein is ______

  Casein molecules associate with each other in tiny, raspberry-like structures called ______– an aggregation, or cluster of molecules often found in colloidal dispersions

  As long as milk keeps its normal acidity, level (pH - 6.6), casein remains stable…if an acid is added, the casein ______to form ______. When cooking, you can prevent curdling by using ______ to thicken the milk. The starch surrounds the casein and prevents coagulation.

  20% of milk protein is ______

  Whey is the ______found in the ______ that remains after fat and casein have been removed from milk

  Whey is also called ______protein. Heat will easily coagulate whey, although heat has little effect on coagulating casein.

  In addition to the proteins, casein and whey, milk contains a number of ______that are also protein molecules. Most of these are ______during pasteurization.

  Another way to coagulate milk is with the enzyme rennin, which is used to clot milk in the first stage of cheese making.

Fats

  Milk is an ______ because small globules of ______are dispersed throughout the water. Around each fat globule is a thin membrane containing proteins, phospholipids and bound water, suspending clusters of fat in droplets.

  ______ – fat droplets form larger clusters that rise and float to the top.

  Cream is milk that is extra rich in emulsified fat droplets

  The fats in cow’s milk are the most complex lipids known. The lipids include over 400 different fatty acids.

  Milk fat contains very little ______ compared to egg yolk.

  The fats in milk influence the flavor, texture and price – the ______fat, the ______ the price.

Carbohydrate

  Milk sugar – ______

  ______– enzyme that breaks lactose into glucose and galactose

  ______– no lactase in intestines – lactose remains undigested, then certain intestinal bacteria attack and ferment the lactose, producing acids and gas – this causes discomfort

  ______milk products (yogurt, buttermilk)

Vitamins and Minerals

  Minerals – in the form of salts – chlorides, phosphates, citrates of potassium, ______, sodium, and magnesium (salts prevent milk from curdling)

  Trace ______ – cobalt, copper, iodine, iron, magnesium, nickel, molybdenum

  Vitamins:

  ______ – breaks down when exposed to light – this is why milk cartons are opaque

  Thiamin

  Niacin

  Vitamin A

Processing Milk

  ______ – heated to a high temperature for a short time – destroys ______bacteria

  ______ – eliminates creaming – under pressure, milk is forced through small openings to break down fat and keep the fat molecules permanently separated

  ______ – Vitamin D is added (helps the body absorb calcium and phosphorus), and Vitamin A (a fat-soluble vitamin) is added back to low-fat milk products (by law)

Types of Milk Products

  ______ milk

  ______ – in sealed box – long shelf-life (3 months or more if unopened)

  Concentrated milk – ______– ______ is added to stabilize the casein – off white color is caused by chemical reaction of lactose and amino acids

  ______ – 50% of water is removed, 44% sugar is added – used in dessert recipes

  ______

  Half and Half – 10.5% to 18% fat

  ______cream or Coffee cream – 18% to 30% fat

  ______cream – 30% to 36% fat

  ______cream – at least 36% fat

  Whipping cream is often UHT pasteurized to lengthen shelf life

  ______ – dried into powder form – milk solids can be reconstituted by adding water

  Non-fat dry milk has longer shelf life – no fat to oxidize and spoil the product

  ______ milk products

  ______ – buttermilk, yogurt, cheese

  Process – pasteurized, lactic-acid bacteria breaks down lactose (lowers the pH), ______(starter is added), ______, ______

Cheese

  Made by ______the ______protein

  ______– aged – makes the flavor and texture distinct

  Moisture content varies

  ______– Parmesan, Romano

  ______– Cheddar, Colby, provolone

  ______– Muenster, Roquefort

  ______– Brie, Camembert, mozzarella

  ______– cottage cheese, cream cheese, mozzarella

Storing Milk Products

  Keep it ______!!

  Use closed, ______containers – ______is light-sensitive

  ______cans or UHT boxes after opening

  Store non-fat dry milk at room temperature – keep moisture out

  Keep cheese cold, although it tastes better when served at room temperature – wrap carefully to keep it from drying out

Cooking with Milk

  Making ______

  More fat = higher ______(thickness) = better whipped cream

  Cold temperatures increase viscosity – whip cream when it’s ______!! Use cold mixing bowls and beaters

  Whip small amounts

  Adding sugar decreases the volume and stiffness of the foam, so add sugar after whipping the desired amount of air into the foam

  ______Milk

  Milk ______– it’s highly sensitive and highly reactive to heat – heat denatures and coagulates the whey proteins of fresh milk, causing them to precipitate, then it settles to the bottom, and scorches – use a ______to prevent this

  When heated till scalding in open containers, evaporation causes a ______to form on top (marshmallow or whipped cream prevents this)

  ______can occur at high temperatures – use low temperatures and non-acid ingredients to prevent this

  ______action

  Some desserts use rennet to make clotted milk - use moderate temperatures so enzyme is not inactivated

  ______

  Causes milk to curdle (like when you add fruit to your milk and cereal or lemon juice to tea and milk)