Milk Flashcards
What is the biological definition of milk?
The liquid normally secreted by female mammals for nourishment of their young.
What is the chemical definition of milk?
A colloidal suspension of organic and inorganic food substances consisting of water, fats, carbohydrates, proteins, mineral salts, gases, some bacteria, enzymes, and vitamins.
What is the legal definition of milk?
The whole, clean, fresh, lacteal secretion obtained by the complete milking of one or more healthy cows, properly fed and kept, excluding that obtained within 15 days before and 5 days after calving or such longer periods as may be necessary to render is practically colostrum free.
The least accurate definition.
What percent of milk is composed by water?
87%
What percent of milk is composed of fats?
3.8%
What percent of milk is composed of protein?
3.5%
What are the major milk proteins?
Casein, albumin, globulin
What percent of milk’s TOTAL composition is casein?
2.8%
What percent of milk’s TOTAL composition is albumin and globulin?
0.7%
What percent of milk is composed of lactose?
5%
What percent of milk is composed of ash?
0.7%
What percent of milk is solids not fat (SNF)?
9.2%
What is the total solids percent for milk?
13%
Describe milk fats
Milk fats contribute 48% of the calories in whole milk. It exists as temporary emulsion with globules suspended in liquid (think of oil in water).
What are milk fat globules made of, and what characteristics do they have?
Fat globule membrane: made up of phospholipids, proteins, and enzymes; has a negative charge
Fat globule membranes are the interface between the fat and water components of milk. They are lightweight, and rise to the top of milk because of their low density and low specific gravity.
Describe the chemical composition of fat globule membranes.
Triglycerides: 98-99%
Phospholipids: 0.2-1.0% (almost exclusively found in the fat globule membrane)
Sterols: 0.25%
Waxes: trace
Vitamins A, D, E, and K (fat soluble vitamins) trace
Describe the composition of triglycerides.
glycerol backbone with three fatty acids
the fatty acids attach to the glycerol backbone
Describe the composition of phospholipids.
Contains glycerol, fatty acids, phosphate groups, and a nitrogen containing base.
They are partly soluble in fat and partly soluble in water.
Why are phospholipids good emulsifying agents?
A portion of the molecule in soluble in water and the other portion is soluble in fats.
Describe the composition of fatty acids and describe the types.
There are generally over 500 different fatty acids in milk.
They are composed of a carbon chain attached to a carboxylic acid functional group.
Saturated fatty acids have no double bonds between the carbons and can be solid at room temp
Unsaturated fatty acids have double bonds between the carbons in the chain, and can be liquid at room temp
What percent of fatty acids in milk lipids are saturated.
66% or 2/3
What percent of fatty acids contained in milk lipids are unsaturated?
34% or 1/3
Why does cream rise to the top?
Fat has a lower specific gravity than the water component of milk and is less dense that it as well.
Describe lactose.
Lactose contributes 30% of the calories in whole milk
It is a disaccharide composed of glucose and galactose.
It is a true molecular solution, meaning it cannot dissolve out of milk.
It is also lower solubility and less sweet than sucrose.
Describe milk proteins.
Milk proteins are the second highest quality protein after egg protein.
They contribute 22% of the calories in whole milk.
The are comprised of amino acids.
Milk proteins exist in colloidal dispersion (think of sand in water), meaning they are suspended in the fluid component of milk.
Describe the composition of an amino acid
Contain a carboxylic acid group, a carbon chain, and an amine group.
They form proteins by forming peptide bonds between other amino acids.
What is lysine and why is it important?
Lysine is an amino acid found in milk. It is important because it is an amino acid that is deficient in many corn products. Surplus lysine in milk helps offset the lysine deficiencies found in these cereal products.
What percent of milk proteins are Caseins?
82%
Describe caseins
Caseins are milk proteins that comprise 82% of the total protein in milk. They are contained as micelles, a weblike structure surrounded by electrical charges that help keep it suspended in the milk.
There is current interest in A1/A2 caseins, aka beta caseins
What are the whey proteins?
lactalbumin and lactoglobulin
What percent of milk proteins are lactalbumin and lactoglobulin?
18%
Describe the whey proteins
The whey proteins comprise 18% of the total milk proteins, but there is more lactalbumin than lactoglobulin.
Immunoglobulins are important because they provide immunity to newborns through colostrum
What is colostrum?
The first milk formed by the mammary glands immediately following the delivery of a newborn. They contain many immunoglobulins to help provide newborns with immunity.
What is the nutritional value of the milk proteins?
They are second only to egg proteins in total nutritional value
What are the types of curd formation?
Enzyme and acid
Describe the enzyme formation of a curd and the enzymes involved.
The enzymes renin or pepsin hydrolyze kappa casein to paracasein and binds with calcium ions. The caseins clot to form calcium paracaseinate, which is the curd. This curb contains casein, calcium, water, vitamins, and enzymes. This is a hard, elastic curd that contains minerals.
Sweet whey is left over from the curd. It contains water, lactose, minerals, albumins, globulins, and vitamins.
Describe acid formation of a curd.
Adding acid to milk can coagulate the proteins in it. At a ph of 4.67, milk reaches its isoelectric point, where it has an equal number of positive and negative charges. They combine and caseins precipitate out at this pH of 4.67. This produces a soft curd with no minerals.
Describe the importance of enzyme curd formation in the manufacture of cheeses.
Hard curds (via renin or chymosin) comprise around 80% of the cheeses. Some examples are American, cheddar, Swiss, etc
Describe the importance of acid curd formation to the manufacture of cheeses.
Soft curds produced by acid curd formation make up the remaining 20% of cheeses. Some examples are cottage cheese, ricotta, cream cheese, etc.
What are some minor constituents of milk?
Vitamins, enzymes, somatic cells, leucocytes
Describe the differences between vitamins.
Some vitamins are fat soluble and are influenced by diet. These include Vitamin A, D, E, and K. Other Vitamins, such as vitamin B and C, are water soluble.
Vitamin A and D are usually fortified during milk processing.
What factors influence the composition of milk?
- Species
- Breed of dairy cattle
- Stage of lactation
- Stage of milking
- Feeds and feeding
- Diseases
- Genetics
- Season of year
- Age
Describe the composition of milk shortly after postpartum compared to 72 hours postpartum.
Milk immediately after postpartum is much higher in total solids, namely protein. Albumins and globulins are higher in order to provide the newborn with immunity. 72 hours postpartum, the total solids count decreases by half.
How do the seasons impact milk composition?
Seasons determine what food will be available to the mother, which can influence milk composition.
Fat composition of milk during the first streams compared to last streams?
1.1% during the first streams of milking compared to 7.6% during the last streams of milking.
Define organoleptic
How something appeals to the senses; based on multiple factors
What is considered a desirable flavor of milk?
Bland, slightly sweet
Describe the absorbed flavor defect of milk
Absorbed flavors occur when the animal eats aromatic weeks or feed before milking.
The flavor includes feedy, cowy, or barny flavors. The flavor can also take on the aromatics consumed by the animal, like garlic or onion for instance.
Absorbed flavors can be prevented by not feeding the animals aromatics around milking time.
At home, these flavors can be prevented by keeping milk away from aromatic items in the refrigerator.
Describe the bacterial flavor defect of milk
flavors: acid, malty, putrid
causes: microbes, improper cooling (bacteria grow better in warmer temps), poor sanitation
prevention: proper cooling procedures and sound milk handling practices
this defect can be dangerous due to the microbes present
Describe the oxidative rancidity flavor defect of milk
Flavor: papery or cardboardy
Causes: oxidation of unsaturated fatty acids by breakage of the double bonds; can be caused by UV light or elemental catalysts like Cu and Fe
Prevention: using stainless steel equipment, proper packaging and storage conditions; utilizing pigmented cartons to block light
Describe hydrolytic rancidity (lipolyzed) flavor defect of milk
flavor: bitter, soapy
causes: enzymatic hydrolysis of triglycerides; the lipase enzyme liberates free fatty acids, causing the flavor change
prevention: proper handling and storage, avoiding excess agitation and stirring; pasteurization to denature the enzymes
What are the processing procedures for milk?
Standardization, pasteurization, homogenization, separation, ultrafiltration, reverse osmosis
What is standardization?
Standardization is adding skim milk to commercially available milk to establish a baseline fat content and to stabilize the milk’s composition. It stabilizes the composition of commercially available milk by reaching the desired fat content.
What is pasteurization?
Heating milk to kill pathogenic bacteria in order to protect public health
LTLT
low temp long time pasteurization
145 degrees F for 30 min
HTST
high temp short time pasteurization
161 degrees F for 15 minutes
UHT
ultrahigh temp
280 degrees F for 2 seconds
developed to help countries with poor refrigeration; can change flavor
Homogenization
A process that involves reducing the size of fat globules so that milk fat does not separate in the milk fluids.
It is achieved by pumping milk through a series of screens under pressure to reduce the size of the fat globules
Separation
The process of using centrifugal force to separate milk components, especially in skim milk or cream
Ultrafiltration
separates components based on molecular size
Reverse osmosis
concentrates milk components by reducing water for shipping purposes
What are the ideal storage conditions for milk?
- cool (under 40 degrees F)
- sanitary
- odor-free environment
- no exposure to fluorescent lighting or sunlight (to prevent oxidative racidity)
What are milk grades based on?
The facilities and sanitary conditions of the farm it was produced in.
Describe Grade A milk
Grade A milk is over 90% of the fluid milk in the U.S., and it the only milk allowed to be used as fluid milk.
Describe Grade B milk
Typically produced in older facilities, Grade B milk makes up around 10% of milk. It is mainly used for dairy products and cannot be used for fluid milk
What is the fat content of skim milk?
0.5%
What is the fat content of reduced fat milk?
2%
What is the fat content of lowfat milk?
1%
Describe fortified milk
Fortified skim or low-fat milk where solids are added back to bring up the SNF up to 10.25%, which improves flavor. Vitamin A and D are also added.
Describe ice cream
has at least 10% fat and is highly regulated
Describe sherbert
has a lower fat and solid count that ice cream, but has more sugar
describe butter
contains at least 80% fat
describe eggnog
comprised of milk products, eggs, sweetener; at least 6% fat
describe cheese
there are over 400 varieties, and the microorganisms present in cheese provide the specific desired product
describe yogurt
Yogurt is usually produced via fermentation with the lactobacillus bacteria. Greek yogurt has more protein than conventional yogurt but takes more milk to produced (4 lb. to 1 lb. for normal milk).
How much whole milk is required to produce butter?
21.2 lbs
How much whole milk is required to produce cottage cheese?
6.2 lbs
How much whole milk is needed to produce a gallon of ice cream?
12.0 lbs
How much whole milk is needed to produce cheese?
10 lbs
What is an imitation product of milk?
They look and taste like milk, but are nutritionally inferior products
What are substitute milk products?
Substitute milk products usually have a higher nutritional value that imitation products.
Describe lactose intolerance
Lactose intolerance results in bloating, nausea, and diarrhea. It is caused by a deficiency in the lactase enzyme, and is relatively common worldwide.
Some alternatives for people with lactose intolerance include smaller servings of dairy products, reduced lactose products, fermented products, or tablets to reduce discomfort
Describe milk allergies
A milk allergy is a reaction to a specific milk protein, and is common in children under the age of 3.
What mineral is most abundant in milk?
Potassium (K)
Why would an animal become anemic if they are raised only on milk?
Milk is a poor source of iron (Fe).
Why are Vitamins A and D fortified during milk processing?
Vitamin A helps with vision, and Vitamin D helps bind calcium in the body to be used in the bones.
What flavor defects of milk can pasteurization prevent?
Bacterial: by killing the microbes in the milk
Hydrolytic rancidity: by denaturing the lipase enzyme that liberate fatty acids from triglycerides (which causes the bitter, sour flavor)
What are cultured dairy products?
These are dairy products where microorganisms are used in their production.
ex. cheese and yogurt
Describe the composition of a hard curd.
casein, minerals (mostly Ca and P), some water, enzymes (renin)
Describe the composition of sweet whey
lactose, water, water soluble vitamins (B and C), albumin, globulin, minerals (except Ca and P)
Describe the composition of a soft (acid) curd
casein, albumin, globulin, some water
Describe the composition of acid whey
water, minerals, water soluble vitamins (B and C), lactose, and lactic acid
What is in buttermilk?
milk proteins, lactose, water, water soluble vitamins (B and C), and minerals
