Milk & Cheese Flashcards
1
Q
What are the constituents of milk in solution?
A
- Water soluble vitamins (good source of Riboflavin, thiamin/niacin/ascorbic acid in small amounts)
- Minerals (⅓ of Ca, K, Mg, Na)
- Lactose (sugar) which participates in Maillard browning reaction
- Salts
2
Q
What are the constituents of milk in colloidal dispersion?
A
- ⅔ of Ca, Phosphorous
- Proteins: whey proteins + casein proteins
3
Q
What are the constituents of milk in emulsions? What kind of emulsion is milk and how does it keep in that emulsion?
A
- Milk fat
- Fat-soluble vitamins (A and D)
- Milk is fat-in-water emulsion (fat is dispersed, water is continuous)
- Fat in milk exists as globules kept in emulsion by an emulsifying layer around fat globules
- Emulsifying layer is composed mainly of lipoproteins
4
Q
What are the 4 stabilizing factors in milk?
A
- Brownian movement
- Like charges repelling
- Water of hydration
- Kappa in casein
5
Q
What are the kinds of milk proteins?
A
- 80% casein proteins (alpha, beta, kappa) which exist with calcium and phosphate as calcium phosphocaseinate/casein micelle
- 20% whey proteins (lactalbumin and lactoglobulin)
6
Q
What is homogenization?
A
- Milk is pumped under extreme pressure through very small holes
- Prevents fat globules from forming larger clusters which rise to surface of milk
- Reduces size of fat globules
- Fat globules permanently distributed as a very fine emulsion throughout milk (continuous phase)
- Better ratio of emulsifying layer to fat globules
- Homogenized milk is whiter, more opaque, easier to digest when fat particles are smaller
7
Q
What is pasteurization?
A
- In Canada, all commercial fluid milk and cream must be pasteurized
- Destroys pathogenic microorganisms by heating
- Especially Tuberculosis brucellosis
- 15 seconds at 72 C (high temperature, short time or HTST)
- 2 seconds at 138 C (ultra-pasteurizing)
- 99.4% of bacteria are destroyed, the remaining 0.6% are good bacteria
8
Q
What is the difference between regular commercial milk and PurFiltre milk?
A
- Milk is passed through extremely fine filter to remove bacteria, then pasteurized
- Separate fat from whole, 2%, or 1% milk
- Filter milk
- Add fat back
- Pasteurize milk
- Increased level of purity of milk (99.9% bacteria gone)
- Longer storage time and shorter pasteurization time
- Some say there is better flavour
9
Q
What are cultured dairy products?
A
- Inoculated milk with non-pathogenic bacterial culture (Lactobacillus bulgaris or Streptococcus thermophilus)
- Ferments lactose into lactic acid
- pH decreases from 6.6 to 4.6
- IEP of casein proteins
- Casein proteins denature and coagulate
10
Q
How do you denature whey proteins? What happens and how do you prevent it?
A
- Denatured by heat only, stabilizing factors no longer present
- Denatured whey proteins precipitate out of colloidal dispersion
- Settle to bottom of container
- If you continue to overheat, causes the whey proteins to scorch the bottom of the pot
- To prevent overheating (direct heat), use double boiler (<100 C) to heat milk
11
Q
What can denature casein?
A
- Acid
- Polyphenolic compounds
- Enzyme rennin
12
Q
How can acid denature casein?
A
- Casein micelles are colloidally dispersed at pH of milk (6.7)
- Negative charges around casein micelles repel each other and keep micelles stable
- Adding acid lowers pH by adding H+
- Neutralizing negative charges around micelles
- Overall charge on micelles becomes 0
- Brings casein micelles to their IEP (4.6), unstable, micelles are said to be denatured
- Adhere together forming larger, less stable molecules
- Precipitate out of colloidal dispersion
- Heat accelerates reaction
13
Q
How can polyphenolic compounds denature casein?
A
- Found in light coloured, low acid fruits, and vegetables (potatoes, apples, asparagus, mushrooms, green peas, strong tea and coffee)
- Remove layer of water of hydration around casein micelles
- Micelles denature and adhere together and form larger, less stable molecules
- Precipitate out of colloidal dispersion (curdling)
- Heat accelerates reaction
14
Q
How can the enzyme rennin denature casein?
A
- Enzyme extracted from stomach of calves
- Not present in milk
- Synthetically produced in a form called chymosin
- Used mainly in cheese-making industry
- Rennin removes Kappa casein (which is an extra 4th stabilizing factor) from casein micelle
- Alpha and beta casein readily denature, but calcium does not split off from casein micelle
- Weak, unstable Calcium Caseinate GEL forms
15
Q
What happens during the cheese making process?
A
- By the end of cheese making process, proteins (whey and casein) are denatured and coagulated
- Water-in-fat emulsion has formed
16
Q
What happens when you age/ripen cheese?
A
Changes in texture (changes in protein)
- Firm, tough & rubbery to softer & crumbly
- Cheese blends better
Changes in flavour (changes in fat)
- Mild & bland to mellow & tangier
17
Q
How do you overheat cheese and what occurs?
A
- Too high a temperature or moderate temperature for an extended period of time (eg. leaving cheese mixture in double boiler for too long)
- Cheese proteins become over-coagulated
- Tough and stringy cheese due to excessive H bonds are happening along polypeptide chain
- Overcoagulated proteins shrink due to bonds forming and squeeze out water = water on top of cheese
- Fat emulsion breaks = oily layer on top of cheese
18
Q
What properties define cheeses?
A
Cheeses which melt are:
- Medium/high in moisture
- Medium/high in fat
Cheeses which blend must:
- Melt well
- Be aged/ripened (changes to proteins during ripening allow cheese to blend)
19
Q
How do you make a good whipped cream foam?
A
- Use cream with ≥ 32% fat (lipoproteins in emulsifying layer around fat globules)
- Use cold temperatures (≤ 4 C)
- Cream, beaters, and bowl at refrigerator temperature (4C or lower)
- Fat globules become more solid
- Cream is thicker, making it easier to incorporate air bubbles (higher volume)
- Solid fat globules clump together more easily on surface of air bubbles (more stable foam)
20
Q
What occurs when you whip/beat whipped cream?
A
- Incorporates air bubbles
- Disrupts emulsifying layer around fat globules causing them to clump together
- Fat globules collect on surface of air bubbles
- Results in stable foam (longer time before bubbles burst and foam collapses)
- Denatures lipoproteins in emulsifying layer which collect on surface of air bubbles
- Results in an even more stable foam
21
Q
How do you prevent denaturation of casein?
A
- Minimize heating
- Use double boiler (<100 C)
- Heat only to serving temperature (do not boil) - Minimize time acid ingredient and casein in milk are together
- Adding milk just before serving (last step then “serve immediately”) - Thicken water phase around casein micelles
- Physically prevents denatured casein micelles from adhering together and precipitating out of colloidal dispersion
- Starch if product involves heat (gelatinized)
- Gelatin if conditions are cold
22
Q
What occurs when you add heat to whipped cream foam?
A
If you heat whipping cream, it will melt
You cannot coagulate whipping cream, therefore you cannot make a permanent foam like meringue
23
Q
What occurs when you add sugar to whipped cream foam?
A
- Decrease foam volume if added too soon and increase time to create foam (add after partial foam is created)
- Decrease foam stiffness (softer peaks)
- Decrease chance of over-beating which would result in butter
- Increase foam stability (longer time before foam collapses)
