Page 7 - exemple

B- Fehling test for reducing sugars

Pour 10 ml of water in a test tube A, and 10 ml of a glucose
solution in a test tube B. Add to each tube 2 ml of the blue
colored Fehling solution.
Heat the mixture in tubes A and B.
In tube A, the blue coloration persists whereas a brick red
precipitate appears in tube B indicating the presence of a
reducing sugar. Fehling test gives a positive result with all
the monosaccharides and disaccharides except sucrose.

Doc 3- Identification of reducing
sugar.

3 Iodine water test for starch (performed at cold temperature)

Pour few drops of iodine water (brown orange) in a test tube
containing a solution of cooked starch. A dark blue
coloration appears. We say that the reagent of starch is iodine
water.
Starch is found in potatoes, rice, wheat…
Starch is a carbohydrate without a sweet taste. It is soluble in
hot water only. Its molecule is formed by an association of
many glucose molecules.
By performing the iodine water test directly on a piece of
bread or on a slice of potato or banana, a dark blue
coloration appears indicating the presence of starch
(Doc. 4). Doc 4- Iodine water test on a piece
of bread.

4 Identification test for lipids

Place or scrub a foodstuff rich in lipids on a paper; a
translucent spot appears.
Wait for an hour, we observe that the spot becomes larger
and doesn’t disappear when heated.
Oil and milk creme have the same properties. They are lipids.

Doc 5- Only lipids leave a
translucent spot on a paper.

Food 11