Topic 7: Gels and Emulsion Flashcards
Why is oil immiscible with water?
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
what are “fat-in-water” examples of emulsions?
hollandaise (egg yolk w/ butter), mayonnaise (oil, egg yolks, vinegar/lemon juice), milk or cream
*fat dispersed in water
What are examples of “water-in-fat” emulsions?
vinaigrette (vinegar and oil), butter, margarine
*water dispersed in fat
what are the steps to making an emulsion?
- two phases, continuous phase (container of emulsion) and dispersed phase(the other liquid dispersed within)
- Emulsifier - liaisons between the two liquids to stabilize it (eg. amino acids, lecithin in egg yolks)
- mechanical force, shaking, stirring or blending, energy is used to bbreak up the dispersed phase and distribte it throughout the continuous phase evenly
- Stabilizer (or Thickner) to create more stable emulsion, makes the dispersed droplets more difficult to move. also thickens the emulsian
What are some examples of stabilizers (or thickeners)
porteins, starch, pectin, plant particles, and corn starch
what makes milk an emulsion?
- 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.
what is the outer surface of casein micelle made of
negatively charged kappa casein, these charges repel one another and thus are kept in solution
what does the addition of acids do to the kappa-casein molecules
the acids protonate kappa-casein molecules which causes them to lose their negataive chage, then binding together and becoming visible clumps in the milk
how does blending/whipping cream result in whipped cream?
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
what happens when you keep whipping the cream?
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
What packing material is ideal for milk?
glass, it preserves milk flavor. plastic can also work, as it can also help maintain freshness in absence of light exposure
what kind of emulsion is ice cream?
fat in water emulsion, also foam
What state of matter is ice cream?
ice cream contains all three states, ice crystals (solid) fat globules, air bubbles (gas) dispersed in water/sugar (liquid)
Marketing grade of ice cream
Regular : ~10% milk fat
Premium : 12~14% milk fat
Super-premiu: >14% milk fat (denser, smoother, richer)
what is MNSF?
Milk solids non-fat which are proteins and mineral salts
what are the ingredients of ice cream?
water (ice crystal), milk fat, sweetner, air MNSF (milk solids non-fat ie, proteins and mineral salts),, eggs, stabilizers (gums, gelatin), flavoring and coloring
Why must more flavor be added into ice cream?
Cold temperature decreases our tastebud sentivity so it may “mute” flavors
What determines the texture of ice cream?
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
What added affect does sugar have on ice cream?
sugar can lower the freezing point of the ice cream mixture so that it doesnt freeze completely, this creates a softer texture
Why ice cream shrinks as it ages?
the ice cream mix collapses over time and trapped air escapes
Why the ice cream tastes differently, usually worse when it
melts and is refrozen?
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.
Why is ice cream mix churned?
- promotes formation the numerous ice crystal for a smooth texture
- Encourages the mixture to be homogenized disrupts fat globules from rejoining, and dispersing them
- increases volute by incporating air
What are gel foods
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)
What is the composition of gelatin?
a mixture of proteins extracted from collagen found in bones, hids and connective tissues of animal
low nutrition content
What is the composition of agar?
a mixture of two polysaccharides: agarose (found in cell walls of algae) and agaropectin
a vegetarian gelatin substittue and high fiber content
what is pectin?
a strucural polysaccharide found in the skin & core of raw fruits
pectin functions as a structural cement that holds cell walls together
How is yogurt gelatinized
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
list various methods of coagulating cheese
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
What happens after cheese is coagulated into curds
curds are treated by cutting > heating > salting > knitting / pressing > cheese
what is a traditional Chinese gelatinization method?
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.
