Question 3 Answer

(a) Method A

Measure 1g of each type of flour and add to a test tube,respectively.

Add 5 ml of distilled water to test tube.

Add 6 ml of 1% Sodium or Potassium hydroxide followed by a few drops of aqueous Copper (II) Sulfate. (Biuret Test)

Note Colour Change in each.

Method B

Measure 1g of each type of flour and add to test tube respectively.

Add few drops of ninhydrin.

(b) Method A

Solution turns from blue to purple.

Method B

Solution  turn blue or purple.

(c) Wheat flour has more dietary fiber than white flour.
However White flour has more carbohydrate than wheat flour.
Wheat flour has more protein, fat and moisture than white flour.

(d) Gluten  helps the dough to rise, keep its shape and often gives the final product a chewy texture.

Yeast and baking powder are raising agents.

When sugar and moisture are added to yeast,fermentation begins and energy is released.

Yeast cell grows aerobically:

C12H12O11 + H2      2C6H12O6

C6H12O6+ 6O2      6 CO2 + 6 H2O + energy

C6H12O6        2C2H5OH+ 2 CO2

(Balanced equations)

Trapped carbon dioxide expands on heating which cause the dough to rise.

2NaHCO3(s)             Na2CO3 (s) + H2O (g) + CO2(g)

Baking powder is broken down by heat and carbon dioxide evolved. The trapped carbon dioxide expands on heating which the dough rise.

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