Milk Flashcards
How is milk synthesized and secreted?
Mammary gland cells
Smallest unit of milk synthesis?
Alveolus within the alveoli are secretory epithelial cells
Mary gland structure
Duct system is connected to?
Duct system connected to secretory and supporting tissues
Vascularization of tissue
Tissue is well vascularized so we can see blood vessel and capillaries
Important because milk contains components that come from the circulation
PH of milk
6.6. when we think about the pH of milk
Similar to the pH of plasma (slightly below neutrality)
Where is lactose synthesized
Lactose synthesized at Golgi apparatus into vesicles travels o apical end of cell and fuse to membrane where they are sent to the lumen
Majority of cows
Holsteins have the best milk production
Jersey cow milk
produce milk that have a slightly higher far content (example would be used in products like clotted cream)
Basics of cooling milk
Plate heat exchangers will be in most dairy farm facilities to being it down from 37 C to 4C (lower end of danger zone)
Plate and one side has cold water and the other has milk flowing over it. A good cold conductor and that is how the milk is cooled down so rapidly
Milk collection
Milk is the collected by the dairy farmers funded through quota and supply management of the industry. Everyone’s milk is combined/ picked up if you produce milk in Ontario. Picked up by dairy farmers of Ontario
Milk testing before pickup
Can test for fat level, microbes (to make sure animals are healthy)
Majority of milk content
Water
Fat content
3.4- 5.1 (jersey cow on higher end)
Protein content in milk
Controlled at 3.3 - 3.9
Lactose in milk
Not variable at 4.9 - 5
Ash minerals in milk
minerals and salts in the milk. We can recognize the major players are calcium, magnesium, phosphate, citrates (citric acid salts)
Freezing point of milk
-0.57 Close to water but because it has lactose and minerals it is slightly below zero
Casein protein content in milk
80% of total protein
Composition of types of casein
Alpha 40, beta 25, K 9
What do alpha S and beta ungerdo?
phosphorylated undergo post translational modification
Kappa caseins
unique because they are glycosylated sugar group as most translational modification
Whey characteristic
Easy to denature above 70 C and start water soluble and turn insoluble with heat
What is responsible for milk protein allergies?
Whey
What is integral to structure of mammary gland?
Capillaries and vascular system are integral to structure of Mary gland
Butyic
Butyric is responsible for butter flavour that we appreciate in butter
Milk fat processing first thing
Removal os skin
Result of skin
What happens is we know lipid or fat is less dense than the aqueous component
Fat rises because it is less dense so we remove it and the fat does towards butter or whipping cream
Homogenization of milk
homogenize the fat by forcing milk through tiny droplets the fat will be broken up into tiny droplets
The tiny fat droplets are much less likely to separate and rise in the milk product
To help with a uniform or consistent product it undergoes homogenization to break up the fat into tiny droplets
Milk also undergoes pasturization
Temp for milk homogenization
72 C
Milk minerals: calcium
Calcium is important in addition to magnesium
Calcium is soluble assocaited with whey and semisoluble associated with the casein
Also present in milk
Citrates, calcium phosphate, sodium chloride
What does heating milk do to flavour
Has a different flavour from the fresh cold milk because the sulphur amino acids in the caseins have undergone some bond exchanges resulting in the release of hydrogen sulphide and that is the key component in the different of flavour and aroma when we have heated milk. Milk on its own has a fairly delicate flavour so the H2S is easier to detect in the milk
Effect of acid on milk
lactic acid fermentation in making yogurts. Basically yogurt making represents the formation of a gel or coagulant and facilitated by lactic acid bacteria. Through production of lactic acid you are modifying the pH of the environment.
Milk starts with pH of 6.6 because of the proximity to circulation system to the milk production process. The lactic acid will release hydrogen ions so H+. We know because of phosphorylation of caseins they will have a net negative charge which will be neutralized or cancelled out by the hydrogen ions. If the caseins have negative charges we become familiar with like charges repelling each other. If you then take away the negative charge and make it neutral this means the proteins no longer repel each other and they come together and trap moisture in the structure which gives you the gel in yogurt. The concept of an isoelectric point can also help to understand this pI (isolectic point short hand) of 4.6 for caseins.
Ph where the protein has no charge
isoelectric point so there is a balance between negative and positive charges. Protein is uncharged so its solubility is at its lowest point. Protein not soluble at isoelectric point which also contributes to formation of gel and coagulation. Semi solid gel that traps moisture and majority of the gel is the casein proteins
Enzyme in cheese making? Name? Where it comes from?
The enzyme is called renin (commerical name is rennet but it contains the rennin enzyme). The enzyme came from the stomach lining of calves and when it comes from the stomach lining of the calf it is a liquid form and in this case it is called cymosin (chyme) (chymosin is rennin in its liquid form). It contains the rennin enzyme which is responsible for gel that is formed (this was seen in the egg and dairy lab)
Main caseins in milk
Main caseins in milk are alpha s and beta caseins.
How does casein exist in milk?
It is important to known the caseins exist in the milk in the from of casein micelles which are different than that fat micelles of chylomiccrons.
Casein micelles
micelle floats around in the milk.
What is a casein micelle?
Caseins Micelle is raspberry shaped individual alpha s and beta caseins and kappa caseins.
What stabilizes casein micelles
Kappa stabilizes casein micelles so they dont interact with each other. R
Characteristics of kappa
Kappa has hydrophobic and hydrophilic. Phobic is burried inside raspberry in contact with alpha s and beta hydrophilic points to the acqeous component of milk.
What does renin do to the casein micelle? What does the do for teh cheese making process?
Rennin cleaves off the hydrophilic portion of the casein micelle and can no longer float around. The micelles now want to cluster around together and trap moisture and the coming together of the casein micelles trapping moisture is the gel formed is the beginning of cheese making. You get to cheese by draining out the moisture (Asiago/ parmasean) for the mozzarella which is soft and high moisture will contain more liquid
What is fouling?
Fouling or surface fouling is consequence of denaturation of whey protein
How does fouling result?
Whey proteins denature and lose solubility so they become precipitated on the surface of the cooking pot. Film contains protein, calcium and lactose which means that if you heated it for an extended period you would see browning which is non enzymatic browning. Tendency for fouling during the pasteurization process.
Temp when most pasturization is done?
72 but historically it was done at 63 (both are outside of the danger zone but cranking temp of to 72 means you dont have to heat the milk for as long. Instead of 20-30 minutes at 63 degrees you can heat it for seconds at 72 C. You minimize change in the flavour of your milk this way
Skin formation
consequence of denaturation and dehydration at the surface of the heated milk. Denaturation is mostly associate with the whey proteins.
When does skin develop
Not stirring and heating milk and then letting it sit at the top and dehydrate
Avoiding skin in milk
Agitation when heating, denaturation will happen but skin wont rise to top
Curdling is teh result of?
Have to heat to quite a high temperature. Curdling is similar to what we discussed when forming custards when we heat to 100 C we denature whey and caseins and if you limit the amount of stirring and agitation it is possible to have a milk gel form. Only in very high temperatures so not usually seen in most kitchens
Lactic acid yogurt pH
4.1-4.9
Bacteria in yogurt?
Lactobacillus bulgaricus
Streptococcus thermophilus
Which ferment lactose
Look up acidophilus and bifidus
Says something about yogurt cheese
Evaporated milk
60% water removed with 7.5 milk fat and 25.5 total solids
How is evaporated milk sterilized?
115 to 118
Condensed milk and sweetened content
28 % solid and 8% fat
Sour cream bacteria
Streptococcus lactis, lactic acid
