Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
53 Cards in this Set
- Front
- Back
|
Cows' Milk Composition |
87% Water 4.8% Lactose 3.5% Protein 3.5% Fat 0.2% Non-Protein nitrogen 0.7% Ash |
|
|
Milk fat is composed of: |
-98% of milk lipids are triglycerides -the fat globules in the milk make an oil-in-water emulsion |
|
|
Lactose |
-a disaccharide prominent in milk -Lactose is formed form glucose and galactose -Lactose crystals are responsible for the sandy texture in some ice creams |
|
|
Whey |
-liquid that drains from the curd of clotted milk -whey contains lactose, some proteins, water-soluble vitamins and some minerals |
|
|
Casein |
-collective name for the milk protein fraction which precipitates at pH 4.6 -casein micelles effectively block light transmission and make milk opaque |
|
|
Curd |
Milk precipitate that contains casein |
|
|
Rennin |
-proteolytic enzyme from the stomach lining of calves that eliminates the protective function of x-casein in micelles and results in curd formation |
|
|
Carbohydrates |
-one cup of milk contains 11-12 g of lactose -Lactose provides 30% of energy from milk -Lactose gives a sweet taste -Lactose contributes to the browning of the Maillard rxn |
|
|
Proteins |
-Casein (80% of the proteins are Casein)
-Whey |
|
|
What pH does the milk have to reach for the casein to form a soft curd?
|
When the pH of milk is adjusted to 4.6, the casein precipitates to form a soft curd, which can be separated from teh remaining liquid (whey) |
|
|
Casein precipitation is achieved through two different mechanisms? |
1) Milk acidification 2) Use of rennin |
|
|
1) Milk acidification |
-acid moves the pH of milk closer to the isoelectric point of one type of casein (x-casein), which is the protein that is preventing the micelles from precipitating |
|
|
2) Use of Rennin |
rennin, a proteolytic enxyme found in the stomach of calves, hydrolyzes the hydrophilic portin of the x0casein that was primarily responsible for the stabilizing effect of x-casein on the surface of the casein micelles -in the presence of calcium, the newly formed compound, para-x-casein, becomes insoluble -consequenly the micelles can then aggregate to form a gel |
|
|
What are the 2 main whey (globular) proteins? |
-Alpha-lactalbumin -Beta-lactoglobulin -these constitute 70-80% of total whey proteins |
|
|
Hold Method Pasteurization |
-milk is heated to 65*C and held for 30 minutes before it is cooled |
|
|
HTST |
72*C for at least 15 seconds -causes less of a cooked flavour |
|
|
UHT |
138-145*C for at least 2 seconds |
|
|
Homogenization |
-mechanical process where milk is forced through tiny apertures under a pressure of 14-17MPa, which breaks up fat globules into units so small that do not separate from the milk |
|
|
Characteristics of Homogenized Milk: |
1. no separation of fat globules from the milk 2. more viscous 3. less stable to heat 4. more sensitive to light-oxidation 5. foams more readily 6. curds formed form homogenized milk is softer |
|
|
Drying Milk Process |
-it is condensed by removing 2/3 of the water and then spray dried to less than 5% moisture level -when dried, the milk powder consists of lactose, fat in globules or free, and protein in the form of casein micelles and precipitated whey protein |
|
|
Fermentation |
-the goal is the production of lactic acid -there is thickening associated w/ fermented products is the result of the association of casein micelles, often accompanied by beta-lactoglobulin -when a large amount of beta lactoglobulin is bound to the casein micelles, a fairly stable gel is formed and syneresis is minimal |
|
|
Buttermilk |
thickened bc of fermentation |
|
|
Yogurt |
Acidified to the point where a gel forms as a result of fermentation and controlled heat |
|
|
Whey fermentation |
produces such comparatively sweet cheeses as Mysost and Gjetost |
|
|
Fluid milks and Foams |
Fluid milks are not able to form stable proteins unless there is a sufficient concentration of protein -reconstituting skim milk powder to 3x the concentration of whole milk (protein content of 10.5%) results in a fairly stable foam |
|
|
Cream Foam |
Stabilized by fat |
|
|
Whipping Cream |
Whipping cream with a minimum fat content of 30% produces very stable foam due to the amount of fat present and to the state in which the fat is present in the cream -during beating, particles of air are surrounded by membranes containing fat globules and stabilized by a film of partially coagulated protein |
|
|
Temperature and Foam |
--the clumping of fat globules will only occur when the fat is in a semi-solid state; the fat is quite firm and gives rigidity to the cell wall when chilled -room temp cream will prevent the formation of a rigid film |
|
|
Over-beating |
causes revrsal to the water-in-oil emulsion, resulting in butter |
|
|
Cream |
-contains the high fat portion separated from whole milk during creaming process |
|
|
Light Creams |
-ranges from 10-18% -half & half, cereal, coffee and table creams |
|
|
Heavy Creams
|
-ranges 30-40% fat content -whipping cream |
|
|
Minimum Fat Content for Stable Foams
|
-30% |
|
|
Fermented Milks |
-Cultured buttermilk, sweet acidophilus milk, kefir and Lactaid |
|
|
Sweet acidophilus milk |
Inoculated w/ Lactobacillus acidophulus, but it is not allowed to ferment so it is sweet |
|
|
Lactase |
Digests a good portion of lactose into glucose and galactose |
|
|
Yogurt |
-a fermented milk product in a gel form -microorganisms used to ferment milk to yogurt include Streptococcus thermophilus, & Lactobacillus delbrueckii subsp. bulgaricus |
|
|
Ice Cream |
-a frozen mixture of cream w/ added milk solids and flavourings into which a large amount of air has been stirred -the sweeteners lower the melting and freezing points of ice cream |
|
|
Stabilizers in ice cream |
-guar gum, alginates, or carrageenan -they can bind water and increase the viscosity of ice cream before mixing |
|
|
Monoglycerides in Ice Cream |
Serve as emulsifying agents
|
|
|
Small crystals |
-small crystals are imperitive to achieve the right texture |
|
|
Desirable level of overrun in commercial ice creams |
Over 70% |
|
|
Two common defects found in ice cream |
sandiness and iciness |
|
|
Cheese production |
requires the formation of a curd and removal of a considerable amount of water (whey) |
|
|
Acid precipitation |
used to make cottage cheese and cream cheese |
|
|
Rennin |
-used for making most cheeses -used to convert x-casein into para-x-casein -para-x-casein then participates in curd formation by uniting with calcium, which forms an insoluble material -the gel formed is cut to release whey -then, gentle heating and squeezing |
|
|
Moisture Content of Cheese |
Usually 37 - 40% |
|
|
Blue Cheese |
Penicilium roqueforti -gives a special colour to the cheese while breaking the fat globule membrane so that lipase can breakdown the fat molecules and release FFAs |
|
|
Jarlsberg & Swiss Cheese |
-holes caused by carbon dioxide formation by barious Propionibacterium species or other lactic acid producing bacteria
|
|
|
Camembert |
Penicillium camemberti -this mold is the source of proteolytic enzymes that migrate slowly into the Cheese during ripening and catalyze proteolysis to produce a very soft to almost fluid cheese when overripe |
|
|
Melting Properties of Cheese |
largely due to its age and the moisture and fat levels -casein proteins bonded together break down in the presence of heat -young cheese have high moisture content and weak protein structure, allowing protein to flow at lower temps -old cheese have a stronger structure and melt at higher temperatures |
|
|
Reduced Fat Cheeses |
-fat is important so instead of removing fat (one method) you could replace the fat with gums |
|
|
Processed Cheese |
made by heating natural cheeses and adding an emulsifying agent , which reduces the size of protein molecules, increases the solubility and teh water-binging capacity and kills microorganisms |
