Slide 8: Milk Overview Flashcards
Define milk
“A white or yellowish liquid consisting of small fat globules suspended in a water solution, secreted by the mammary gland for the nutrition of the newborn”
What are the components of milk?
Ø Water Ø Carbohydrates Ø Fat Ø Protein Ø Minerals & vitamins
What are the solids that make up milk?
Fat + Protein + carbohydrate + Min. & Vit. + enzymes
What are the solid-non-fat (SNF) components of milk?
Protein + carbohydrate + minerals & vitamins + enzymes
What are the components of skim milk?
Ø Skim milk (plasma): Milk - fat
Ø Whey (serum):
Skim milk - casein micelles
What are the proteins of milk?
casein, whey protein, MUN
What is the CHO component of milk?
lactose
A physical definition of milk:
“An emulsion of fat globules and a suspension of casein micelles all suspended in an aqueous milk serum phase”
How are fat globules found in milk?
Fat globules suspended in a relatively stable plasma phase
How are casein micelles found in milk?
Casein micelles in a colloidal suspension in milk serum phase
Strong negative correlation exists between lactose and:
Ø Milk fat
Ø Milk protein;
Protein (%) = 20 - 2.8 lactose (%)
Strong positive correlation exists between ______
milk protein & milk fat
Protein (%) = 1.05 + 0.57 fat (%)
How is milk osmolallity maintained?
Milk osmolality is maintained by lactose and diffusible ions. Therefore a negative relationship exists between lactose concentration and the sum of Na & K
A ______ relationship exists between lactose concentration and the sum of Na & K
negative
In milks where casein micelles are formed, a _______ correlation exists between casein concentration and Ca- P concentrations
positive
There is an ______ relationship between milk nutrient concentrations and suckling frequency
inverse
Species with precocious young secrete milk with _____ protein concentration than those with altricial young
lower
Compare the water content of milk in different mammals
donkey > cow > pig > rat > whale > seal
Variation in water content of milk among various cattle breeds
Holstein > Guernsey > Zebu = Jersey
What are the three groups of salts found in milk and their functions?
1- Ionic form: Na, K, Cl (diffusible). Maintain
osmotic equilibrium of milk with blood
2- Colloidal (nondiffusible) form: Ca, Mg, P, citrate (associated with casein micelles)
3- Diffusible salts of Ca, Mg, HPO–4 . Contribute to overall acid-base balance of milk.
Explain the milk fat’s general features?
Ø The most variable milk component in both concentration & composition
Ø Milks of some species contain little or no fat (e.g. black rhinoceros) while those of aquatic species (e.g. seals) contain > 50% fat
Ø Excellent source of energy (2.25 > protein & CHO)
Ø Adipose tissue (subcutaneous fat) protects the young in cold environment
What are the variations in milk fat among mammals?
Donkey < Human < Cow < Rat < Reideer > Whale < Seal
What are the variations in milk fat in cattle breeds?
Holstein < Brown Swiss < Ayrshire < Zebu < Guernsey < Jersey
What is the physical structure of milk fat?
Most of milk fat is in the form of fat globule
What is the size of the fat globule of the milk fat?
Ø 0.1-15 μm in diameter
Ø Covered by thin membrane
What is the origin of the thin membrane in a milk fat globule?
Ø Origin: apical membrane of the secretory cell
What is the composition of the thin membrane in a milk fat globule?
Ø Composition: Protein & phospholipids
What are the chemical compositions of milk lipids?
Ø Triglycerides (98% in cows, women, 88% in rats)
Ø Phospholipids (0.6% in cows, 0.3% in women, 0.7% in rats)
Ø Diacylglycerol (0.4% in cows, 0.7% in women, 2.9% in rats)
Ø Cholesterol (0.35 in cows, 0.25% in women, 1.6% in rats)
Ø Free fatty acids (0.3% in cows, 0.4% in women, 3.1% in rats
Milk fat contains > _____ fatty acids
400
Fatty acids are composed of
Hydrocarbon chain & carboxyl group
Triglycerides are composed of
Glycerol + three fatty acids
Saturated fatty acids vs unsaturated fatty acids vs polyunsaturated fatty acids
Ø Saturated fatty acids: No double bonds
Ø Unsaturated fatty acids: One or more double bond
Ø Poly-unsaturated fatty acids: Two or more double bonds
What is fatty acid composition influenced by?
Fatty acid composition of milk is influenced by the diet of the lactating female more than any other milk component
What are the sources of variations in milk fatty acid composition?
1- Chain length (short-, medium- or long-chain FA)
2- Degree of un-saturation
3- Position of fatty acids on the glycerol skeleton
C16 and C18 are
Long chain fatty acids
C10 and C14 are
Medium chain fatty acids
C8 and C4 are
Short chain fatty acids
_______ (C16:0) and _____ (C18:1) acids are the most abundant fatty acids in milk of most mammals (elephant & rabbit are exceptions)
- Palmitic
- Oleic
_________ (C18:1) is the most abundant unsaturated fatty acid in milk of most mammals
Oleic acid
Milk of ______ & _______ contain high levels of long chain polyunsaturated fatty acids (> C18:3)
whales
seals
Milk contains _____ proportions of short- & medium- chain fatty acids than the other body tissues
higher
Milk fatty acids of carnivores and sow are mostly _______
C16 & C18
Milk of herbivores contains ______ saturated fatty acid than milk of carnivores
more
Milk of ruminant species contains ______ levels of short-chain fatty acids (< C9) than milk of non-ruminant species
higher
Describe the marine animals milk fatty acids
Ø High levels of polyunsaturated fatty acids
Ø Whales: 27% of fatty acids > C18:3 (short half-life)
Ø Seals: 12% of fatty acids > C18:3
Ø Very low levels of C16:0
Describe the marsupials milk fatty acids
Ø A digestive system similar to ruminants
Ø Milk fat change considerably during lactation
Ø 1-6% fat in early lactation & 11- 35% in late lactation
Ø No short chain fatty acids (< C12) Ø No fatty acids longer than C18
Ø Milk fatty acid composition change considerably during lactation
Ø Early lactation: mostly C16:0 (45%) and some C18:1 (25%)
Ø Late lactation: mostly C18:1 and some C16:0
Describe the rodents milk fatty acids
Ø High levels of short chain fatty acids Ø Rabbits
Ø More than 50% of fatty acids < C12 (mostly C8:0 & C10:0)
Ø Very low levels of C16:0 Ø Rat
Ø ~50% of fatty acids < C14 (C10- C14
What is the dietary significance of milk fat?
Ø Good source of energy
Ø Good source of health promoting compounds such
as conjugated linoleic acid
Ø Important source of fat soluble vitamins particularly vitamin A
Ø Milk fat is rich in saturated fatty acids which may increase blood level of LDL (increase incidence of cardiovascular diseases)
Hypercholesteremic fatty acid
C14, C16
Neutral fatty acid
C4:0-C10:0
Hypocholesteremic fatty acid
C18:1,2,3
What are some general points about milk protein?
☛ Less variable than milk fat ☛ Unique to milk ☛ Contain more essential amino acids than any other natural food ☛ Positive correlation with fat %: ☛ Protein (%) = 1.05 + 0.57 Fat (%)
Variation in milk protein among mammals
Human < Donkey < Cow < Reindeer < Seal < Rat < Whale
Milk nitrogen has 2 components
- Non-protein nitrogen
- true protein
True protein has 3 components
- whey protein
- casein
- fat globule membrane protein
Whey protein has 2 kinds
alpha-lactalbumin
beta-lactalbumin
What are caseins?
Conjugated proteins (linked mostly to a Phosphate group)
Casein precipitates at ____
Precipitate at 4.6 pH or by the action of gastric enzyme chymosin (rennin)
Casein is the milk protein for ____
The main milk protein for many mammalians (not in humans)
What are the 4 types of caseins?
alpha
beta
gamma
kappa
What are the proportions of casein in cows milk?
48% alpha, 36% beta, 13% kappa, and 3% gamma casein
Proportion of casein in milk protein in mammals
goat > cow > sheep > rabbit > pig > horse > human
Where is the cows milk allergy stem from?
reason why cows milk cause a lot of allergies is bc beta lactoglobulin
if you feed the baby with cows milk is also high amount of casein and clot formation happens in the digestive system, of the baby this might cause digestive problems
Define casein micelles
A colloidal particle consisting of casein protein, calcium & phosphate
What are the functions of casein micelles?
☛ Carry large amount of insoluble Ca & P to the newborn for skeletal development
☛ Form a clot in the stomach for more efficient digestion
How is the cheese curd formed?
The bond between phenylalanine and methionine are broken down by chymosin and Ca++
Define whey protein
Proteins in the supernatant of milk after precipitation at the pH of casein precipitation (4.6)
What are the types of whey proteins
☛ beta-lactoglobulins (synthesized in the mammary gland)
☛ alpha-lactabumin (synthesized in the mammary gland)
☛ Serum albumin* (blood protein)
☛ Immunoglobulins (Ig, in colostrum) (blood protein)
What are the general features of beta lactoglobulin?
Ø The most abundant whey protein in ruminant and sow milk
Ø Found in small concentrations in human milk
Ø The exact function is not known
Ø Found in milk of mammals which transport high levels of immunoglobulins in colostrum
Ø The exact relationship between immunoglobulin transport and b-lactoglobulins in not known
What are the general features of alpha lactoglobulin?
Ø Constitutes ~25% of whey protein in bovine milk
Ø Play an essential role in lactose synthesis (part of
enzyme lactose synthase)
Ø Secreted along with lactose in milk
Ø Found in milk of most studied species except certain seals which have no lactose
What are the general features of blood serum albumin?
Ø Characteristic of species (e.g. in cows is called bovine serum albumin
Ø Synthesized in the liver and then transport to the milk through the mammary cell
Ø The concentration of BSA in cow and human milk is 0.04 and 0.06%, respectively.
Ø During mammary infections, BSA can be transported into the milk via leaky junctions between mammary cells
What are the general features of immunoglobulins?
Ø Part of passive immunity transfer to the neonate via colostrum or placenta
Ø Very high in colostrum but very low in milk
Ø Immunoglobulins (Ig) include:
Ø IgA, IgG, IgM
What are the iron-binding proteins found in the milk?
lactoferrin and transferrin
What are the general features of lactoferrin?
Ø Secreted by several organs of the body including the mammary gland
Ø High levels in human milk
Ø Low levels in rabbit, rat and dog milk
Ø Intermediate in cow milk except during involution (high)
What are the general features of transferrin?
Ø Common plasma protein
Ø High levels in milk of rabbit and rat
Ø Low levels in human and dog milk
Ø Intermediate in cow mouse and sow milk
Milk carbohydrates consist of
Ø Lactose Ø Monosaccharides Ø Oligosaccharides Ø Sugar phosphate Ø Nucleotide sugars Ø Free glucose and galactose Ø Free myo-inositol
What are the main features of oligosaccharides?
Ø Main milk carbohydrates in monotremes
Ø Main milk carbohydrates in many marsupials
during early lactation
Ø Higher in human (1-2.5%) than cow milk (0.1-0.2%)
Ø Higher in colostrum in both animals
What are the main features of HUMAN oligosaccharides?
Ø Mature human milk and colostrum contain 12-13 and 22-24 g/liter of oligosaccharides, respectively
Ø There are 130 oligosaccharide in human milk
Ø They constitute the 3rd largest components (after lactose
an fat)
Ø Oligosaccharides may be important for brain development and resistance to infection
Ø Human milk contain large amount in sialylated oligosaccharides than cow’s milk and infant formula
Ø Milk oligosaccharides are NOT digested in the small intestine but digested in the large intestine (prebiotics)
Ø Human milk contains N-acetylglucosamine (the bifidus factor) necessary for the growth of Bifidobacterium bifidum
Ø The lactic acid bacteria (B. bifidum) reduce the intestinal pH and inhibit pathogen growth
Ø Oligosaccharides prevent pathogens from adhering to the epithelial cells (pre-requisite for infection)
What are the main features of lactose?
☛ Disaccharide consists of glucose& galactose
☛ The major carbohydrate of milk in most mammals
☛ The least variable milk components
☛ Occurs only in milk and is digested by the intestinal enzyme lactase
ØNot the main carbohydrate in marsupials
ØMilk of some seals contains very low levels of lactose
Ø Milk of California sea lion does not contain lactose
Variation in milk lactose among mammals
Donkey > Human > Cow > Sheep > Whale > Bear
What are the features of milk carbohydrates of marsupials
Ø ~ 7% (2 wk postpartum) to 11% (26 wk postpartum)
Ø Fall sharply after 26 wk
Ø In the first 26 wk, the main carbohydrates is oligosaccharides
Ø In late lactation, the main carbohydrates are monosaccharides
What is the importance of lactose?
☛ Major osmole in milk
Differences in osmotic pressure is responsible for
drawing water into the milk
☛ Readily source of simple sugars for the newborn
☛ Fermented substrate for lactic acid bacteria needed for many fermented dairy products (e.g. Yogurt)
