Starch

Question 1

Sources of starch & starch granules:

Answer 1

Potato, corn, rice and wheat. important energy source in human food. Some starches are not degradable by human: act as a fiber.

Question 2

Starch structure:

Answer 2

1. Amylose: 25% . Linear molecule. Glucose units alpha 1,4 linkage.
   2.Amylopectin: 75%. branched molecule . Linear parts 1-4 linkage but the branched parts are 1,6 bond.
   Both of them present as a helix in the starch granules.
   Amylopectin is present in the crystalline region and in the amorphous region you have some parts of amylopectin together with amylose.

Question 3

GELATINIZATION OF STARCH: dissolving starch, what happen if we heat the solution of starch to get the starch dissolve in water ? (4)

Answer 3

1. Gelatinization temperature around 60ºC, the viscosity is going up because the starch granules starts to swell.
2. Loss of polarization cross.
3. Peak viscosity: highest point in viscosity,
4. Disruption of starch granules: break apart , lose of viscosity , getting separate amylose and amylopectin molecules.
   If we made the starch solution after gelatinization, and we leave it at room temperature, an a certain point retrogradation is starting to take place, this means the viscosity increased again because the starts molecules that were first in solutions start to connect again with each other, this is an irreversible reaction .

Question 4

Modification of the starch:

Answer 4

1. Physical modification: first heat up the starch solution and dry it, you get a powder that is called ISNTANT STARCH (soluble in cold water).
2. Chemical modification: hydrolysing the starch and then dry, you get THIN-BOILING STARCH. When you add this to the food is give much lower viscosity because the starch molecules are much smaller after modification.
3. Chemical modification: linking the starch molecules to each other (e.g. with phosphate), you get CROSS-LINKED STARCH. This is less sensitive to stirring.
4. Chemical modification: substituting the starch, you get SUBSTITUTED STARCH, retrogradation will not take place that easy.

Question 5

When cooling down the starch solution after gelatinization, retrogradation can take place.
• Complete the curve for retrogradation.

Answer 5

Retrogradation means that starch molecules start to connect each other a little bit and because of that the viscosity is going up again. So after some time you will slowly see an increase again.