The Biochemistry of Milk

How do you milk a cow? Video http://www.moomilk.com/faq.htm#To%20make

The Complex Nature of Milk Milk supplies the calcium for building bones and teeth, especially during adolescence Milk is 87% water However that’s a solvent for over 250 chemical compounds, milk sugar (what is the name for milk sugar_____?____) water-soluble vitamins and trace minerals and salts

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

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

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 cow’s milk are most complex lipids, over 400 different fatty acids Click For Milk Experiment

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.

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

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

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 milk’s nutritional value, creating a slight loss of thiamin, vitamin B12, vitamin C DO YOU THIN THAT DRINKING UNPASTURIZED MILK IS BETTER FOR YOU?

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.

Fortification Fortification = the addition of a nutrient to a food Ex. What nutrient is milk fortified with___?___ Without vitamin D, your body can’t 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

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 it’s prepared by heating for a short time at ultrahigh temperatures. Placed in special sealed packages Flavor improves over time

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

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)

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 it’s cooled down to stop or slow bacterial growth What are some examples of cultured foods???

Buttermilk/Sour Cream/Yogurt Buttermilk – used to be the fluid left over from producing butter, today it’s 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 41°C-45°C for around 8 hours

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

Storing and Cooking with Milk How many of you leave milk on your table when eating dinner?? Is that safe?? – Even if it’s for ½ hour? Milk retains it’s 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?

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

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

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

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