Topic 7: Gels and Emulsion

Question 1

Why is oil immiscible with water?

Answer 1

The attractive force between molecules of the same liquid is greater than the attractive forces between the two different liquids (if similar then they tend to be soluble)

Fats and oils are nonpolar
water is polar

Question 2

what are “fat-in-water” examples of emulsions?

Answer 2

hollandaise (egg yolk w/ butter), mayonnaise (oil, egg yolks, vinegar/lemon juice), milk or cream

*fat dispersed in water

Question 3

What are examples of “water-in-fat” emulsions?

Answer 3

vinaigrette (vinegar and oil), butter, margarine

*water dispersed in fat

Question 4

what are the steps to making an emulsion?

Answer 4

1. two phases, continuous phase (container of emulsion) and dispersed phase(the other liquid dispersed within)
2. Emulsifier - liaisons between the two liquids to stabilize it (eg. amino acids, lecithin in egg yolks)
3. mechanical force, shaking, stirring or blending, energy is used to bbreak up the dispersed phase and distribte it throughout the continuous phase evenly
4. Stabilizer (or Thickner) to create more stable emulsion, makes the dispersed droplets more difficult to move. also thickens the emulsian

Question 5

What are some examples of stabilizers (or thickeners)

Answer 5

porteins, starch, pectin, plant particles, and corn starch

Question 6

what makes milk an emulsion?

Answer 6

• fat globbules are mixed into an oil-in-water emulsion
• casein proteins are in colloidal suuspension
• fat globules (larger) and casein micelles (smaller but large enough to deflect light) contribute to the opaque white color.

Question 7

what is the outer surface of casein micelle made of

Answer 7

negatively charged kappa casein, these charges repel one another and thus are kept in solution

Question 8

what does the addition of acids do to the kappa-casein molecules

Answer 8

the acids protonate kappa-casein molecules which causes them to lose their negataive chage, then binding together and becoming visible clumps in the milk

Question 9

how does blending/whipping cream result in whipped cream?

Answer 9

the addition of tiny air bubbles when blending or whipping cream. the whipping action strips away the protective outer membrane of the fat globules, allowing the fat to join together, forming bubbles around tiny pockets of air. The fat holds air suspended in liquid stable

Question 10

what happens when you keep whipping the cream?

Answer 10

the fat globules break open and release the fat molecules. The hydrophobic fat molecules clump together and mix to form larger solid fat and pushes out the liquid. This results in the creation of butter and buttermilk

Question 11

What packing material is ideal for milk?

Answer 11

glass, it preserves milk flavor. plastic can also work, as it can also help maintain freshness in absence of light exposure

Question 12

what kind of emulsion is ice cream?

Answer 12

fat in water emulsion, also foam

Question 13

What state of matter is ice cream?

Answer 13

ice cream contains all three states, ice crystals (solid) fat globules, air bubbles (gas) dispersed in water/sugar (liquid)

Question 14

Marketing grade of ice cream

Answer 14

Regular : ~10% milk fat
Premium : 12~14% milk fat
Super-premiu: >14% milk fat (denser, smoother, richer)

Question 15

what is MNSF?

Answer 15

Milk solids non-fat which are proteins and mineral salts

Question 16

what are the ingredients of ice cream?

Answer 16

water (ice crystal), milk fat, sweetner, air MNSF (milk solids non-fat ie, proteins and mineral salts),, eggs, stabilizers (gums, gelatin), flavoring and coloring

Question 17

Why must more flavor be added into ice cream?

Answer 17

Cold temperature decreases our tastebud sentivity so it may “mute” flavors

Question 18

What determines the texture of ice cream?

Answer 18

size of ice crystals, number/size of air bubbles and % of milk fat

If the ice crystals are smaller and more evenly distributed it will be smoother, larger crystals have a coarser texture, more fat also helps with smoothness

Question 19

What added affect does sugar have on ice cream?

Answer 19

sugar can lower the freezing point of the ice cream mixture so that it doesnt freeze completely, this creates a softer texture

Question 20

Why ice cream shrinks as it ages?

Answer 20

the ice cream mix collapses over time and trapped air escapes

Question 21

Why the ice cream tastes differently, usually worse when it
melts and is refrozen?

Answer 21

Ice cream quality is best when first
purchased because any increase in
temperature melts the small ice crystal. The extra water is taken up by the
remaining crystals, making them larger
and the ice cream more grainy and rough.

Question 22

Why is ice cream mix churned?

Answer 22

1. promotes formation the numerous ice crystal for a smooth texture
2. Encourages the mixture to be homogenized disrupts fat globules from rejoining, and dispersing them
3. increases volute by incporating air

Question 23

What are gel foods

Answer 23

a jelly-like solid that though mostly liquid behave like solids due to three dimensional cross-linked network within the liquid
gels are a dispersion of molecules of a liquid (dispersed phase) within a solid (continuous phase)

Question 24

What is the composition of gelatin?

Answer 24

a mixture of proteins extracted from collagen found in bones, hids and connective tissues of animal

low nutrition content

Question 25

What is the composition of agar?

Answer 25

a mixture of two polysaccharides: agarose (found in cell walls of algae) and agaropectin

a vegetarian gelatin substittue and high fiber content

Question 26

what is pectin?

Answer 26

a strucural polysaccharide found in the skin & core of raw fruits

pectin functions as a structural cement that holds cell walls together

Question 27

How is yogurt gelatinized

Answer 27

fresh milk is left in a container with the bacteria (Lactobacillus acidophilus) Lactic acid is produced as lactose ferments which unfolds the casein proteins which ten links together and creates a soft gel

Question 28

list various methods of coagulating cheese

Answer 28

enzyme coagulation (rennin or rennet)
acid coagulations (lemon juice/vinegar) it inoculates the milk with bacterial culture that acidfies the milk by converting lactose to lactic acid

Question 29

What happens after cheese is coagulated into curds

Answer 29

curds are treated by cutting > heating > salting > knitting / pressing > cheese

Question 30

what is a traditional Chinese gelatinization method?

Answer 30

water chestnut powder, for water chestnut cake. It has a lot of proteins, fiber and carbohydrates and is added to rock sugar, cane sugar, oil and water.