Quiz 4 Flashcards
What is the Primary Component of Milk Fat?
Triglycerides = 3 FA + Glycerol
Contains some Phospholipids
Where do FA come from?
Synthesized in the Mammary Gland
Uptake from the Diet
Uptake from Body Reserves
What makes milk fat unique?
Butter is solid but spreadable at room temperature
It contains many fatty acids
Contains Short and Medium Chain FA
Saturated Fat
Why are FA in 2 Carbon Increments?
Acetate used for synthesis has 2 C, Butyrate has 4 C
Why does the Dairy Cow produce some odd chain FA?
Microbial Digestion generates odd C chains
How are 4-16 Carbon Fatty Acids Synthesized
- Feed Carbohydrates are Fermented
- Acetate and Butyrate are produced and enter circulation
- Acetate forms Acetyl-CoA and Malonyl-CoA and Butyrate forms butyryl-CoA in the MEC. These combine to synthesize Fatty Acids
- Glucose enters the Pentose Phosphate Pathway to Generate Glycerol-Phosphate
- In the ER, FFA combine with glycerol to form triglycerides
Which FA can be synthesized in the MEC?
16C Chain Fatty Acids and Smaller
Where do Preformed Fatty Acids come from?
Adipose Triglycerides are broken down into glycerol and FFA and enter circulation
Feed Fatty Acids form triglycerides that enter circulation and break apart to form glycerol and free fatty acids that can enter the MEC
Where can glycerol in the blood stream go?
Mammary Epithelial Cells - For Milk Fat Synthesis
Liver - For Gluconeogenesis
Causes of Low Milk Fat
Change in Rumen pH
- Influences Rumen Microbe Metabolism
-Decreased Saliva Buffer
-Too much grain/not enough roughage
Biohydrogenation
Rumen Bacteria hydrogenate (saturate) polyunsaturated fatty acids
Where does milk protein come from
90% is synthesized from free amino acids
Where do amino acids come from?
-Proteolysis of feed protein and microbes
-Proteolysis of muscle reserves
What are the major milk proteins
Alpha, Beta, Kappa, and Gamma caseins
Beta-lactoglobulin
Alpha-lactalbumin
What are the Mammary Gland Essential Amino Acids?
Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine
Methionine
Histidine
Arginine
Leucine
Lysine
How are other non-essential amino acids produced?
Enzyme Pathways convert and synthesize amino acids from the essential amino acids through transamination and deamination
Some glucose carbons enter the Krebs cycle and can serve as a Carbon source for amino acid synthesis
Which amino acids are taken up by the MEC in excess of their concentration in milk for synthesis of new amino acids
Arginine
Valine
Leucine
Isoleucine
Which amino acids are taken up by the MEC but are not present in milk
Ornithine
Citrulline
What is significant about Kappa Casein?
It is the key protein in cheesemaking and cows with BB Kappa Casein genotypes produce 4-7% more cheese
What ate the kappa casein geneotype frequencies for Jerseys and Holsteins?
Holstein: 65% AA, 30% AB, 5% BB
Jerseys: 2% AA, 25% AB, 72% BB
How does water get into milk
Milk is isoosmotic with plasma and water transfer/diffusion into milk is dependant on solute transfer into milk
What are the Main Milk Solutes?
Lactose
Proteins (Caseins, Blood Proteins)
Ions (Na, K, Cl)
Minerals (Ca, P)
How are ions secreted into milk?
Lactose, Ca, and P can not diffuse freely and are concentrated by cell membranes and the Golgi
Na, Cl, K follow the concentration gradient into the vesicle or alveolar lumen
Lactose draws water into the lumen through osmosis
What is the relationship between K and Na normal milk
Milk is high in K and low in Na
What are the characteristics of abnormal milk?
Tight junction between cells lose integrity (leak)
- Influx of neutrophils, Sodium, Calcium and blood proteins
- Lower concentration of lactose and potassium
- Higher electrical conductivity
Characteristics of Calcium and Phosphorus in milk
Exist in soluble form bound to milk casein
- Ca ~25% soluble
- P ~44% soluble
The Golgi Concentrates C and P to 3 times the cytoplasmic C and P concentrations
What causes the uptale of Ca & P by the mammary gland?
Dietary intake and Bone Reserves through the action of parathyroid hormone
What are the Trace Elements in Milk
Iron - Bound to lactoferrin and casein; protects MG from bacterial growth
Zinc & Selenium - Bound to Casein
Sulfur - Contained as cross links in methionine, cystine
Cobalt - Contained in Vitamin B-12
Iodine - Actively Concentrated in milk
What are sources of Iodine in milk?
Actively Concentrated
Contamination
- From Iodine Teat Dips/Sanitizers
- From Iodine uterine treatments
- Radioactive iodine
What is the Pasteurized Milk Ordinance definition of milk
“lacteal secretion, practically free from colostrum, contained by the complete milking of one or more healthy cows. Milk that is in final package form for beverage use shall have been pasteurized or ultra-pasteurized, and shall contain not less than 8.25% milk solids not fat and not less than 3.25% milk fat.”
Milk Composition from Cows
Protein Total % = 3.5%
Casein % = 2.8%
Whey Protein % = 0.7%
Fat % = 3.7+%
Carbohydrate % = 4.8%
Ash % = 0.7%
Percent Water in milk
85.5 to 89.5%
Averages 87.5%
Fat Content in milk
3.9% and rising in recent years
Protein Content in Milk
3.4% CP and approximately 3.1% True Protein
pH of Milk
pH influences the physical properties of milk
6.5-6.7 is a desirable pH range for milk
Energy Content of Milk
66 kcal / 100 g
Solution
A substance dissolved in water
-May be ionic or non-ionic
-Non-ionic example: lactose dissolved in water with no molecular changes to the structure
-Ionic example: Salts dissolved in water to form electrolytes
Colloidal Solution
Single small protein with an affinity for water molecules dissolved in water. Ex. Whey
Colloidal Suspension
A large aggregate of protein particles with a lower affinity for water molecules as some sections are hydrophobic. Ex. Casein micelle
Emulsion
Suspension of droplets of one immiscible liquid in another. Ex. Milkfat
What make milk white
Fat
Skim milk appears to have a blue tint
What is a milkfat globule’s composition?
The core is approximately 90% triglycerides and the membrane allows it to interact with water due to the phospholipids
They range in size from 0.1 micrometers to 20 micrometers
They have a density of 0.93 g/ml
Protein Concentrations in milk
Casein comprises 80% of total proteins in milk
What are the Functional Characteristics of Milk Proteins
Hydration/Water Binding
Solubility
Viscosity
Gelation
Emulsifying Ability
Foam Formation
Flavor Binding
Electrical Charge (Affected by pH)
Electrical Charge of Milk Proteins
At pH 6.6 the protein molecules have a net negative charge which generate a net negative charge which prevents precipitation from the milk
At approximately pH 4.7 protein reaches its isoelectric point in which there is a net neutral charge and the proteins cluster and fall out of solution
At even lower pH there is a net positive charge and the repulsive forces are reinstituted
What gives skim milk the white/blue appearance?
Casein Micelles - The collection of thousands of casein molecules in interaction refract light
What is the form of casein submicelles
A hydrophobic core of alpha and beta caseins is surrounded by phosphoric acids and kappa caseins which have hydrophilic carbohydrate chains with strong negative charges
What is the form of a casein micelle
A clump of casein micelles with kappa casein more prominent around the outside and calcium phosphate interactions stabilizing the micelle
The carbohydrate chains of the kappa caseins on the outside of the micelle stabilizes the micelle in milk
What affect does rennet have?
Rennet is an enzyme that causes milk coagulation and causes curd formation because the rennet removes the carbohydrate tail from the kappa casein causing it to become unstable in milk
How are whey proteins distinguished from casein proteins?
Denatured by heat/Unfold when exposed to heat
What are the 2 major classes of whey proteins?
a-lactalbumin – important in synthesis of lactose
B-lactoglobulin
How do whey proteins contribute to “cooked” flavor?
Sulfur-containing amino acids in B-lactoglobulin
Sulfur-bridges start to form with heat (pasteurization)
At high temps, volatile sulfur compounds (H2S) released; contribute to flavor
Why is milk a good buffer?
It contains weak acids and bases
Proteins act as buffers and interact with hydrogen ions and hydroxyls
What are the common milk enzymes?
Lipase
Phosphatase
Peroxidase
Catalase
What is lipase?
A milk Enzyme
○Hydrolyzes free fatty acids from glycerol backbone
○ Excess free fatty acids = rancid taste
§ If there is an excess of lipase in the milk then the triglycerides can sometimes be broken down into excess free fatty acids
§ Typically the membrane of the fat globules protects the triglycerides from the lipase but if this membrane is broken during processing, the triglycerides are broken
What is Phosphatase?
A Milk Enzyme
Splits phosphoric-acid esters into phosphoric acid and alcohol
The phosphatase enzyme activity is destroyed by pasteurization
Used to indicate adequate pasteurization
What is peroxidase?
A milk enzyme that transfers oxygen from hydrogen peroxide to other oxidizable substances
Catalase
Splits hydrogen peroxide into water and free oxygen
Low catalase levels indicate a healthy udder
What is responsible for the water in milk?
Lactose is responsible for 80% of the warer in milk
What metabolic changes occur as a result of the mammary system
Increased Metabolic Rate
Increased Blood Flow
Increased Nutrient Supply
If metabolic demands are not met a metabolic disorder will result
What are the functions of the mammary gland
Substrate Breakdown
Create Energy
Synthesize Milk Components
Regulate transport of non-manufactured milk components
What milk components are synthesized in the MEC
Enzymes
Proteins (Casein)
Lipids (Milkfat)
Sugar (Lactose)
What components are transported into milk by the MEC but not synthesized in the cells
Vitamins
Minerals
Water
Ions
Blood Proteins
What are the Main Milk Component Precursors
Glucose
Amino Acids
Acetate
Butyrate
Triglycerides
Free Fatty Acids
Where does circulating glucose originate?
The majority is synthesized from proprionate by the liver through gluconeogenesis
What is glucose used for in the dairy cow?
Glucose in the MEC is primarily used for lactose synthesis (60-70%)
Very little is used for fatty acid synthesis or diverted to Acytyl-CoA for the Krebs Cycle
How much of the blood glucose is used by the mammary gland?
60-85% dependent on stage of lactation
How is Lactose Synthesized in the MEC
- Glucose enters the MEC
- Some glucose is converted to UDP-Galactose in the cytoplasm
- In the Golgi Apparatus, Lactose Synthetase combines glucose and UDP-Galactose to make Lactose
