Food Science: Milk and Milk Products

How is sweetened condensed milk made?

*15% sugar is added to whole or skim milk, which is then concentrated to about 1/3 or 1/4 its former volume. *Because of the high sugar content after concentrating (42%), the milk is not sterilized after canning (sugar acts as preservative).

What changes occur when cheddar cheese is heated to relatively high temperatures? What precautions could be used to avoid undesirable changes?

*At first, cheddar (and other hard cheeses) soften and melt. *At high temperatures, separation of fat occurs. Fat separation occurs because proteins shrink and pull together, which squeezes out the fat. This results in development of tough/rubbery curd, stringiness, and tendency to harden when cooled. *Avoid these changes by finely grating/grinding the cheese to prevent overheating. Cook cheese sauces in double boiler over low heat with continuous stirring. Always heat cheese over low heat for the shortest amount of time possible!

What are factors that may alter the composition of raw milk.

*Breed of cow (some produce more fat than others) *Time of milking *Feed consumed (will effect nutrient content and flavor/color of milk) *Environment temp *Season *Age and health of cow *How much they milk the cow: Hind milk (last milk in udder - contains fat) vs first milk (first milk out of the udder - contains carbs and proteins)

Casein is stabilized by a negative charge. How does the addition of salt (CaCl2) affect milk?

*Casein coagulates. *Salts interact with the electrical charges on the surface of proteins, which enables conflicting electrical charges to be reduced to absolute minimum, which favors denaturation and coagulation of protein.

Casein is stabilized by a negative charge. How does the addition of rennin affect milk?

*Casein is precipitated. *Calcium remains attached to casein. *The enzyme splits off the hydrophilic portion of κ-casein, which was primarily responsible for stabilizing effect of κ-casein. *In the presence of calcium, this para-κ-casein becomes insoluble and the micelles aggregate into a gel.

Casein is stabilized by a negative charge. How does the addition of acid, acidic foods, or acid producing bacteria affect milk?

*Casein precipitates when acid is added (it coagulates/curdles). *Acid shifts the pH closer to the isoelectric point of κ-casein, which is the protein that keeps the casein micelles from precipitating. *The negative electrical charge on the surface of the micelle is counteracted by the positive charges of the H+ from the acid, which means the repulsive forces of negative charges no longer keep the micelles apart. *Calcium is released to whey.

What is the effect of temperature and viscosity on whipping cream?

*Cold cream whips better than warm cream, so you should chill the cream, bowl, and beater before whipping. *Low temperatures give the cream more viscosity which furnishes more fat globules for clumping. *Low temperatures results in clumping of the fat during agitation (good), whereas warm temperatures results in increased fat dispersion during agitation (bad).

What are some distinguishing characteristics of milk fat?

*Composed of triglycerides, phospholipids, and sterols *Short saturated fatty acid chains *Forms oil-in-water emulsion in milk, the globules are surrounded by a milkfat globule membrane (lipid-protein complex with some carbohydrates) *Less dense than the watery portion of milk, so floats the the surface when it's not homogenized. Homogenization makes fat dispersion more stable.

What is the effect of addition of sugar on whipping cream?

*Decreases the volume and stiffness of product and increases whipping time. *Because of this, add after cream is stiff or just before serving. *If just before serving, use powdered sugar since it dissolves faster.

How does exposure to direct sunlight effect milk?

*Develops an off-flavor (it is oxidized). *Loss of some nutrients occurs, such as riboflavin and vitamin A.

What effect does heating milk have on mineral dispersion?

*Dispersion of calcium phosphate is decreased and some of it precipitates. *Precipitates on top as scum.

How does hydrolytic rancidity effect milk?

*Fats react with water to give a bad smell and taste. *It has "spoiled". *Triglycerides react with three water molecules to give glycerol and 3 fatty acids.

How does freezing effect milk?

*Film of proteins that acts as an emulsifier around fat globules is weakened or ruptured. *This causes fat globules to coalesce. *Dispersion of protein and calcium phosphate decreases and they tend to settle out on thawing (decreases whiteness).

What factors affect the flavor of milk?

*Flavor is bland and slightly sweet. *Heat processing can affect flavor depending on time/temp of heat (may taste slightly cooked). *Feed consumed by cows *Bacterial action *Chemical changes in milk *Absorption of foreign flavors (can lead to off flavors) *Oxidation of phospholipids *Exposure to light *Fermentation

How is non-fat dry milk made?

*Fresh pasteurized skim milk has 2/3 of its water removed under a vacuum. *Then it is sprayed into a chamber of hot filtered air. *This produces a fine powder with low moisture. *It can also be made by spraying a jet of hot air into concentrated skim milk (foam spray drying).

What is the milk content of light whipping cream, heavy whipping cream, light/coffee cream, half and half, and commercial sour cream?

*Half & half = 10.5-18% fat *Commercial sour cream = 18% fat Light/coffee cream = 18-30% fat *Light whipping cream = 30-35% fat *Heavy whipping cream = 36+% fat

What are some of the major enzymes found naturally in milk?

*Lactase *Alkaline phosphatase *Protease *Lipase *Xanthine oxidase

What effect does heating milk have on flavor?

*Leads to a "cooked" flavor depending on the time/temperature. *Maillard reaction occurs between lactose and amino acids, leads to a distinct flavor.

How does leaving milk at room temperature for 12 hours affect the milk?

*Microorganisms begin to grow and multiply. *Rancidity will occur.

What are the major steps int he process of homogenization?

*Milk is pumped under pressures of 2,000-2,500 lbs per square inch through tiny openings in homogenizer. *A film of adsorbed protein/lipoprotein surrounds each globule, acting as an emulsifier (prevents globules from reuniting).

What changes occur in milk as a result of homogenization?

*Milkfat no longer rises to the surface to form a cream lining. *Fat particles are finely dispersed as a permanent emulsion. *Appears whiter because more light is scattered. *Less likely to develop an oxidized flavor. *Forms a softer curd in the stomach which aids in digestion.

What are the various types of process cheese and what is the difference between them?

*Process cheese: Max 43% water, 47% milkfat. Made by heating natural cheese, adding emulsifiers, and cooling. Emulsifiers prevent separation of fat during cooking. *Process cheese food: Max 44% water, minimum 23% milkfat. Food is comparatively soft, yet firm. *Process cheese spread: 44-60% water, 20% milkfat. Easy spreading onto bread and crackers.

What effect does heating milk have on serum proteins?

*Proteins coagulate (whey proteins start to coagulate ~66˚C, casein coagulates at extended periods over 100˚C). *This is accelerated by increasing acidity and some salts. *Leads to a "cooked" flavor. *Proteins precipitate on bottom of pan.

Discuss rbST and the controversy surrounding its use.

*Recombant bovine somatotropin increases milk production. *It is classified as safe because it doesn't change the composition of the milk in biologically significant ways. *Even if we did consume it, our body doesn't have the receptors to recognize the hormone, it just breaks it down like any other protein. *However, it may be harmful to the animal's health (the cows tend to develop udder infections, and antibiotics used may lead to antibiotic-resistant bacteria in the milk). *It sometimes shortens the life-span of the cow. *Cows typically aren't treated with rbST anymore.

What are the effects of homogenization on the cooking qualities of milk?

*Richer flavor (dispersed fat) *Increased viscosity (dispersed fat) *Whiter appearance (scattered light) *Curdles easier because more fat surface is exposed *Thicker starch mixtures (increased viscosity)

What are some examples of imitation dairy products?

*Soy milk, almond milk, coconut milk, and products made with these (imitation cheese, yogurt, etc). *Nondairy whipped toppings and coffee whiteners (sometimes contain casein or whey).

What is the optimum pH and temperature for rennin action?

*Temperature = 40-42˚C *pH = Faintly acid medium (4.5-4.6)

What effect does heating milk have on dispersion of fat?

*The films of protein that surround fat globules break, which allows the globules to coalesce/come together. *Film forms on top of milk.

What effect does cutting the cheese curd very fine have on the cheese product?

*The finer the curd is cut, the drier the cheese will be. *Example: Cheddar curds are cut very small and fine.

Why does "skin" form on heated milk, and what are methods for controlling it?

*The skin is composed of coagulated protein with some precipitated salts/minerals and fat globules entangled in the mesh. *This is troublesome and can lead to the milk boiling over as pressure increases under the film/skin. Ways to control this: *Covering the pan to decreases evaporation (moisture rains back down on mixture). *Diluting the milk to decrease the concentration of the protein. *Beating the milk as it cools (but another film will continue to form when beating stops). *Foam formation at the surface helps prevent film formation. *Another method/example is whipped cream placed on surface of hot chocolate.

What effect does heating milk have on carbon dioxide?

*There is a loss of dissolved gas in the milk. *Gasses are less soluble in hot/warm milk.

How is evaporated milk made?

*Water is removed in a vacuum pan at 50-55˚C. *A prewarming period of 10-20 minutes at 95˚C is used to prevent coagulation of casein during sterilization. *Heat sterilization occurs after the product is homogenized and canned. *It is also fortified with vitamin D and vitamin A.

What is the effect of amount of whipped cream on whipping cream?

*When whipping large amounts, break into separate smaller portions that tailor to the size of the whipper. *when doing small portions, use a small deep bowl so it is adequately agitated.

What factors affect the color of milk?

*White color is from reflection of light on casein micelles and calcium phosphate salts. *High concentration of carotenes gives a yellow tint. *High concentrations of riboflavin gives a greenish-yellow fluorescent color. *Homogenization makes milk more white. *Feed of the cows affects color.

What is the effect of fat content on whipping cream?

*You need at least 30% fat to be able to whip with ease and produce a stiff product. *40% fat gives better whipping quality because of more solid fat particles.

List the different types of casein and some properties of each.

*α(s1) casein - Joins into micelles. Isoelectric point = 5.1. *α(s2) casein - Joins into micelles. *β casein - Joins into micelles. Isoelectric point = 5.3. *κ casein - Stabilizes tiny casein particles/micelles in colloidal dispersion. Isoeclectric point = 3.7-4.2. *γ casein - Not very abundant. Isoelectric point = 5.8. Casein micelles effectively block light. They are precipitated by acid or rennin. Different types of casein vary in size/shape, amount of light reflected, and if they are coagulated by acid/rennit/solubility/heat.

List the different types of whey and some properties of each.

*β lactoglobulin - Coagulated by heat. Soluble. Isoelectric point = 5.3. *α lactoglobulin - Not as coagulated by heat. Soluble. Isoelectric point = 5.1.

Define rennet

A commercial mixture of rennin and other proteolytic enzymes. Dried extraction of rennin.

Define imitation milk

A product that has been manufactured to resemble milk and can be used in place of milk. Contains no actual milk products. Example: soy milk, almond milk, coconut milk.

How much more protein and calcium does an oz of cheese have compared to an oz of milk?

An oz of cheese has 7x the protein and 5x the calcium than an oz of milk.

Define natural cheese

Any cheese made by clotting milk to form a curd and then concentrating the curd by draining the whey. Variations are made by varying the curd concentration and by ripening with or without the addition of selected microorganisms or other ingredients.

Define filled milk

Any milk, cream, or skim milk that has been reconstituted with fats, usually vegetable oils, from sources other than dairy cows. Has nondairy fat added. Pros: Less saturated fat, cheaper.

Define sweetened condensed milk

Canned milk to which sugar is added. Contains more than 54% carbohydrate because of milk sugar and added sugar. Evaporation of about half of the water and heat treatment to kill of harmful microorganisms precede the canning process.

What are some examples of denaturation/coagulation of milk by heat, acid, rennin, and salt in food preparation. Are these effects desirable or undesirable.

Coagulation by heat: *Can occur during sterilizing canned evaporated milk. (Undesirable.) Coagulation by acid: *Used to make so cheeses (such as cottage cheese), buttermilk, yogurt, and sour cream. (Desirable.) *Occurs while making cream of tomato soup, fruit/milk mixtures, and sherbets. (Undesirable.) Coagulation by rennin: *Used to make lots of cheese. (Desirable.) Coagulation by salt: *Salted/cured meats tend to curdle milk during cooking. Even natural meats contain some salts. (Undesirable.)

Define casein

Collective name for milk proteins precipitated at pH 4.6.

Define sour cream

Cream which has been deliberately fermented by the addition of certain bacteria. Fat = 18%

What effect does heating milk have on rennet clotting?

Decreases action of rennet because the enzyme denatures. At temperatures above 65˚C, no rennet action occurs.

What effect does heating milk have on enzymes?

Denatures enzymes

Why are processed cheese blends more easily melted than natural cheeses?

Emulsifiers added to processed cheese prevent separation of fat during cooking, which is a significant problem in natural cheese.

Define rennin (chymosin)

Enzyme from the stomach lining of calves that eliminates the protective function of k-casein in micelles and results in curd formation.

Define kefir

Fermented milk that is about 3% alcohol because of fermentation by Lactobacillus kefir, which also adds CO2. Fat = varies

Define fat globules

Globules range in size from .1 to 15 μm (micrometers) in diameter. These liquid fat droplets are covered in a membrane of phospholipids and proteins which emulsify the fat.

Define pasteurization

Heat treatment of milk adequate to kill harmful microorganisms.

What does alkaline phosphatase do?

If it has been inactivated it is a indicator that pasteurization is complete.

What is the effect of addition of acid on whipping cream?

Increasing acidity up to 0.3% has no effect on whipping quality, however it does produce as sour taste.

What effect does heating milk have on pathogenic bacteria?

It decreases/kills bacteria.

Who was the first person to make process cheese?

KRAFT

Define whey

Liquid that drains from the curd of clotted milk, contains lactose, proteins, water-soluble vitamins, and some minerals. Curds contain casein and form readily in acidic medium.

Define cultured buttermilk

Low fat or nonfat milk containing S. lactis and L. bulgaricus that has been incubated to produce some lactic acid. Fat = .1%

What creates the aroma of milk?

Low molecular weight/volatile compounds.

Define homogenization

Mechanical process where milk is forced through tiny apertures under a pressure of 2,000 to 2,500 psi, which breaks up the fat globules (3-10 microns in diameter) into smaller units (less than 2 microns in diameter) so that they do not separate from the milk.

Define yogurt

Milk clotted by inoculating with S. thermophilus and S. bulgaricus and fermenting to pH ~55. Fat = 0.1% - 3.25+%

Define whole milk

Milk containing all its constituents as received from the cow or other milk giving animal. Fat = 3.25+%

Define reduced-fat milk

Milk in which some of the milk fat has been removed. Fat = 2%

Define high temperature short time (HTST) ultra pasteurization

Milk is heated to 138˚C for at least 2 seconds. This kills all microorganisms and makes possible the storage of milk at room temperature.

Define regular (hold method) pasteurization

Milk is heated to 63˚C and held there for 30 minutes before it is cooled to 7˚C.

Define vitamin D fortification of milk

Milk that has been fortified with vitamin D, which is not naturally found in milk.

Define instant non-fat dry milk

Nonfat milk that has been dried, moistened until sticky, and then re-dried into spongy aggregates of solid that rehydrate readily without lumping. Really easy to disperse in water. Stores 1-2 years.

Define non-fat dry milk

Nonfat milk that has been preserved by evaporation and reduction into powder. Really hard to disperse in water. Stores 1-2 years.

Define butter

Pale yellow fat substance made by churning cream. Fat = 80%

What is the bacteria that produces holes in Swiss cheese?

Propionic bacteria produces CO2, which creates the signature "holes" in bacteria.

Define processed cheese

Real cheese cut with other, non-cheese ingredients such as salt, food dyes, preservatives, extra dairy or other artificial ingredients. Usually contains ~50% cheese.

Define rbST

Recombinant bovine somatotropin is a bovine growth hormone made in a lab using genetic technology and increases milk production.

Classify cheddar cheese on the basis of ripened/unripened, soft/semi-soft/hard, and ripened by bacteria/mold.

Ripened, firm, ripened by bacteria

Classify colby cheese on the basis of ripened/unripened, soft/semi-soft/hard, and ripened by bacteria/mold.

Ripened, firm, ripened by bacteria

Classify gouda cheese on the basis of ripened/unripened, soft/semi-soft/hard, and ripened by bacteria/mold.

Ripened, firm, ripened by bacteria

Classify swiss cheese on the basis of ripened/unripened, soft/semi-soft/hard, and ripened by bacteria/mold.

Ripened, firm, ripened by bacteria

Classify blue cheese on the basis of ripened/unripened, soft/semi-soft/hard, and ripened by bacteria/mold.

Ripened, semisoft, ripened by mold

Classify camembert on the basis of ripened/unripened, soft/semi-soft/hard, and ripened by bacteria/mold.

Ripened, soft, ripened by mold

Why is the saturated, short chains of butter important for the consistency of butter?

Short chains = solid at room temperature.

Define evaporated milk

Sterilized, canned milk that has been concentrated to about half its original volume by evaporation under partial vacuum.

Define lactose

The disaccharide prominent in milk.

Define fluid cream

The fluid milk product rich in fat obtained by physical separation of raw milk. It is a semisolid emulsion of oil-in-water. Fat = 10.5% - 36% depending on the product.

Why can people who grow up on a dairy eat unpasteurized milk?

They develop a tolerance to the bacteria present in the milk.

Define acidophilus milk

Unfermented milk to which L. acidophilus has been added. Fat = 3.25+%

Classify mozzarella cheese on the basis of ripened/unripened, soft/semi-soft/hard, and ripened by bacteria/mold.

Unripened, firm, n/a (It is sometimes ripened)

Classify cottage cheese on the basis of ripened/unripened, soft/semi-soft/hard, and ripened by bacteria/mold.

Unripened, soft, n/a

Classify cream cheese on the basis of ripened/unripened, soft/semi-soft/hard, and ripened by bacteria/mold.

Unripened, soft, n/a

Outline the gross composition of milk (water, fat, lactose, protein, minerals, etc)

Water = 87.4% Fat = 3.7% Lactose = 4.8% Protein = 3.4% (2.8% casein and .6% whey) Minerals = .7% (Ca, Mg, K, Zn, Fe, vit A, riboflavin, folate)

Define dry whole milk

Whole milk that has been preserved by evaporation and reduction into powder. Less shelf stable than non-fat dry milk because fat can be oxidized and will go rancid.

What is the reaction that takes place during the clotting of milk by rennin (chymosin)?

κ-casein + rennin → para-κ-casein + Ca²⁺ → calcium caseinate gel (coagulated casein) Rennin splits the hydrophilic portion of κ-casein, and the resulting para-κ-casein then forms an insoluble complex with calcium.