Exam 2: Starch

Question 1

Structure of starch

Answer 1

20-25% amylose and 75-80% amylopectin

carbohydrate consisting of a large number of glucose units joined by glycosidic bonds = ploys

Question 2

Gelatinization

Answer 2

add water to starch molecules = formed into a solution 1st. add heat = swells
increase in volume, viscosity, and translucency of starch granules as they swell disrupting their granular structure

breaking down the bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites to engage more water. dissolves the starch granule in water.

Question 3

gelation

Answer 3

formation of a gel upon cooling; agitation during cooling disrupts amylose network that would form

acid & sugar both decrease gelation

Question 4

implosion

Answer 4

Implosion of the starch granule occurs when starch pastes are held at >95oC for several minutes
Implosion causes a ↓ in viscosity of the starch (bad)

Question 5

retrogradation

Answer 5

reversion back to crystalline structure upon cooling of starch after heating

Question 6

syneresis

Answer 6

clear liquid = WHEY = EAT IT
drainage of liquid from a gel (pectin)
liquid escaped the gel: can be stirred back in yogurt
- in cheese: curds + whey

to prevent:
use plastic wrap
thickening agent

Question 7

how added ingredients affect starch solutions

Answer 7

what affect does acid have when we’re coking - plant proteins
gels: acid to a gel or adding sugar; how does that affect the final product w/ respect in viscosity
acid: decreases viscosity bc of acid hydrolysis w/ the gel has formed
sugar: dec; increases translucence affect the appearance of the gel that has been made
avoid gel: (lemon meringue) adding acid on the end bc they are less acid hydrolysis; can make it thinner
firmer gel so when you add lemon juice it won’t change the viscosity too much

Question 8

gel strength

Answer 8

is a measure of the ability of a colloidal dispersion to develop and retain a gel form. In the gelatine world, referred to as Bloom.

It is the force, expressed in grams, necessary to depress by 4mm the surface of a gelatine gel with a standard 0.5” diameter cylinder probe.

Question 9

Extra Credit for final: 
What rice(s) do we use for Risotto?

Answer 9

Arborio & medium grain