Biology practical food test form four

Senkolink Author

Nov 22, 2022

BIOLOGY PRACTICAL: FOOD TEST

Food test is the test that can determine whether a specific food substance is present or absent in a given food sample solution.
The major food tested are:-

Starch
Reducing sugar.
Non-reducing sugar.
Protein.
Lipids.

When carrying out food test the following things should be noted:-

The reagent used for corresponding type of food substance.
Procedure to be followed during testing of a given type of food substance.
Practical report should be in past tense.
The appropriate colour should be observed.
The inference should be made.

TABLE FOR THE FOOD TYPE, REAGENT USED AD REAGENT COLOUR

FOOD TESTED/FOOD TYPE	REAGENT USED	REAGENT COLOUR
Starch	Iodine solution	Brown
Reducing sugar	Benedict’s solution	Blue
Non reducing sugar	Benedict’s solution	Blue
	Dilute Hydrochloric acid (Hcl)	Colourless
	Dilute sodium hydroxide (NaOH)	Colourless.
Protein	Dilute sodium hydroxide (NaOH)	Colourless.
Protein	1% Copper sulphate (CuSO4)	Blue.
Lipids	Sudan (III) solution	Red.

SAMPLE PRESENTATION OF FOOD TEST EXPERIMENTAL RESULTS

SAMPLE no 1

Food tested	Procedure	Observation	Inference
Starch	To 2mls of food sample W in a test tube, 2drops of iodine solution were added.	The colour of the mixture was changed to blue-black colour.	Starch was present
Starch		The mixture retained the colour of iodine solution	Starch was absent
Reducing sugar	To 2mls of food sample W in a test tube, 2mls of Benedict’s solution were added. The mixture was then heated to boil.	The series of colour change was observed from blue, to green, to yellow and finally to brick red precipitate.	Reducing sugar was present
Reducing sugar		The mixture retain the blue colour of Benedict’s solution.	Reducing sugar was absent
Non-reducing sugar	To 2mls of food sample W in a test tube, 2drops of dilute Hcl were added. The mixture was then boiled in a water bath and allowed to cool in cold water. 2drops of dilute sodium hydroxide was added to the cooled mixture followed by addition of 2mls of Benedict’s solution. The mixture then was boiled in a water bath.	The colour of the mixture was changed from blue, to green, to yellow and finally to brick red precipitate.	Non-reducing sugar was present
Non-reducing sugar		The mixture retains the blue colour of Benedict’s solution.	Non-reducing sugar was absent
Protein	To 1ml of food sample W in a test tube, 2drops of dilute sodium hydroxide was added followed by addition 2drops of 1% copper (II) sulphate solution. The mixture then was thoroughly shaked.	The colour of the mixture was changed to purple colour	Protein was present
Protein		The mixture retained the colour of 1% copper (II) sulphate solution.	Protein was absent
Lipids	To 2mls food sample W in test tube, 1ml of Sudan (III) solution was added.	Red ring was formed at the top of mixture	Lipid was present
Lipids		The mixture retained the colour of sudan(III) solution.	Lipid was absent

SAMPLE no 2

Food tested	Procedure	Observation	Inference
Starch	To 2mls of food sample solution W in a test tube, 2drops of iodine solution were added. The mixture was then shaked and allowed to settle.	The colour of the mixtrure was changed to blue-black colour.	Starch was present
Starch		The mixture retained the colour of iodine solution	Starch was absent
Reducing sugar	To 2mls of food sample solution W in a test tube, 2mls of Benedict’s solution were added. Then, the mixture was boiled in a water bath.	The colour of the mixture was changed from blue, to green, to yellow and finally to brick red precipitate.	Reducing sugar was present
Reducing sugar		The mixture retains the blue colour of Benedict’s solution.	Reducing sugar was absent
Non-reducing sugar	To 2mls of food sample solution W in a test tube, 1ml of dilute Hcl was added. The mixture was then heated to boil in a water bath and allowed to cool in cold water. 1ml of dilute sodium hydroxide was added to the cooled mixture followed by 2mls of Benedict’s solution. The mixture then was boiled.	The colour of the mixture was changed from blue, to green, to yellow and finally to brick red precipitate.	Non-reducing sugar was present
Non-reducing sugar		The mixture retains the blue colour of Benedict’s solution.	Non-reducing sugar was absent
Protein	To 2mls of food sample solution W in a test tube, 1 ml of dilute sodium hydroxide was added followed by addition of 1ml of 1% copper (II) sulphate solution. The mixture then was vigorously shaked.	Purple colour was developed	Protein was present
Protein		The mixture retained the colour of 1% copper (II) sulphate solution.	Protein was absent
Lipids	To 2mls food sample solution W in test tube, 1ml of Sudan (III) solution was added. The mixture was then shaked and allowed to settle.	Red ring was formed at the top of mixture	Lipid was present
Lipids		The mixture retained the colour of sudan(III) solution.	Lipid was absent

SAMPLE no 3

Food tested	Procedure	Observation	Inference
Starch	2drops of iodine solution were added in a test tube containing 2mls of tested food solution W.	Colour of the solution changed to blue black	Starch was present
Starch		The solution retained the colour of iodine solution	Starch was absent
Reducing sugar	2mls of Benedict’s solution were added in a test tube containing 2mls of tested food solution W. Then, the mixture was boiled	A series of colour change from blue to green, to yellow and finally to brick red precipitate was observed	Reducing sugar was present.
Reducing sugar		The solution retained the colour of Benedict’s solution.	Reducing sugar was absent
Non-reducing sugar	1ml of dilute Hcl was added in a test tube containing 2mls of tested food solution W. Then it was boiled and cooled. 1ml of Sodium hydroxide was to the mixture followed by 2mls of Benedict’s solution and boiled again.	A series of colour change from blue to green, to yellow and finally to brick red precipitate was observed	Non-reducing sugar was present.
Non-reducing sugar		The solution retained the colour of Benedict’s solution.	Non-reducing sugar was absent
Protein	1mls of sodium hydroxide solution were added in a test tube containing 2mls of tested food solution W followed by 1mls of 1%copper (II) suphate solution. Then, the mixture was shaked well.	The purple colour was observed in the mixture	Protein was present
Protein		The solution retained the colour of 1% copper (II) suphate solution	Protein was absent
Lipids	2drops of Sudan (III) solution were added in a test tube containing 2mls of tested food solution W. The mixture then was shaked and allowed to settle.	Red ring was formed at the top of the mixture	Lipid was present
Lipids		The solution retained the colour of sudan (III) solution.	Lipid was absent

SAMPLE ANSWERS

The table summarizing the digestion process

Part of the alimentary canal (Site of action )	pH medium (optimum pH of the substrate)	Source of enzyme	Digestive juice (secretion)	Enzyme	Food digested	Products of digestion
Mouth	Alkaline	Salivary gland	Saliva	Salivary amylase (ptyalin)	Starch	Maltose
Stomach	Acidic	Gastric gland	Gastric juice	Pepsin	Protein	Peptides
Stomach	Acidic	Gastric gland	Gastric juice	Rennin	Soluble milk protein (caseinogens)	Insoluble milk protein (casein)
Duodenum	Alkaline	Pancreatic gland	Pancreatic juice	Pancreatic amylase	Starch	Maltose
				Pancreatic lipase	Lipids	Fatty acids and glycerol
				Trypsin	Protein	Peptides
Small intestine( ileum )	Alkaline	Intestinal wall	Intestinal juice (Succus entericus)	Erepsin (peptidase)	Peptides	Amino acids
				Maltase	Maltose	Glucose
				Sucrase	Sucrose	Glucose and Fructose
				Lactase	Lactose	Glucose and Galactose
				Lipase	Lipids	Fatty acids and glycerol

STARCH

Natural sources of starch are as follows :-

Cassava
Maize
Millet.
Irish potato
Sweet potato
Wheat.
Rice

Properties of starch are as follows:-

They do not sweet taste.
They are insoluble in water.
They are non-crystalline.
They are macromolecules.
It reacts with iodine to form polyiodide complex which is blue-black in colour. This form the basis for testing starch.

Uses of starch are as follow:-

It provides the body with energy.
It is the food reserve in plant. It is the stored form of carbohydrate in plant

REDUCING SUGAR

Natural sources of reducing sugar are:-

Grapes.
Carrots.
Apples.
Onion
Milk.
Pineapple.
Banana.

Properties of reducing sugar are:-

They are soluble in water.
They have sweet taste. They form sweet tasting solutions.
They are crystalline. They can form crystals.
They are small molecule.
They are reducing sugar.This is because the Benedict’s solution which contain copper (II) sulphate when is mixed with reducing sugar, the copper (II) ions of copper (II) sulphate will be reduced to copper (I) ions which form a brick red precipitate of copper (I) oxide. This for form basis for testing reducing sugar.

Uses of reducing sugar are as follow:-

It provides the body with energy. For example glucose is the most common respiratory which is oxidized during respiration to release energy.
Play role in synthesis of disaccharides. For example when two molecule of glucose are combined through condensation reaction, maltose is formed.
They are used is synthesis of polysaccharides such as glycogen. Glucose is particularly important in this role.

NON-REDUCING SUGAR

Natural sources of reducing sugar are:-

Sugarcane

Properties of Non-reducing sugar are:-

They are soluble in water.
They have sweet taste. They form sweet tasting solutions.
They are crystalline. They can form crystals.
They are small molecule.
They are called non-reducing sugar because they cannot reduce copper sulphate of Benedict’s solution.
Note the following During testing of non reducing sugar :-

Dilute hydrochloric acid used to break down (hydrolyze) non-reducing sugars to reducing sugars.
Sodium hydroxide is used to neutralize the dilute hydrochloric acid.

Uses of non-reducing sugar are as follow:-

It provides the body with energy.

PROTEIN

Natural sources of reducing sugar are:-

Beans.
Peanuts.
Eggs.
Fish
Chicken
Milk.

Properties of protein are:-

They are insoluble in water.
They coagulate on heating. This means that small particles of protein clump together to form bigger particles when a mixture of protein and water is heated.
Protein reacts with sodium hydroxide and copper sulphate to produce violet colour/ purple clour. This is called biuret test.
Note the following during testing of protein

Sodium hydroxide is used to provide alkaline medium for the copper sulphate to react with nitrogen atoms of amino acids.
The purple colour formed during the test of protein is the result of a complex between four nitrogen atoms in the peptide bonds and the copper (II) ion (Cu2+) of Copper sulphate solution.

Uses of proteins are as follows:-

They used for growth and repair of worn out body tissues. The protein we eat are used to make new cells which will make tissues to replace those which are worn out.
They provide body protection and defence against disease. For example protein make antibodies which provide the body with immunity.
They can be used to provide energy when the body lacks carbohydrate and fats. This happen during starvation and when the person falls sick.
They form the structural components to various materials such as nails, hair and muscle fibres.
They are required for the formation of enzymes, hormones, and haemoglobin.
They play role in clotting of blood. This is because the fibrinogen which control blood clotting is protein in nature.
They transport oxygen in the blood. This is because the hemoglobin which transport oxygen is protein in nature.

LIPIDS

Natural sources of lipids are:-

Groundnuts.
Coconuts.
Sunflower.
beef fats
Avocado.
Oyster nuts.

The properties of lipids are:-

They are insoluble in water.
They are soluble in organic solvents such as alcohol, chloroform and ether.
When oil is shaken in water, the oil breaks down into droplets which disperse in water. After few minutes water and oil separates into two layers.
When water is added to a lipid that has dissolved in an organic solvent a white milky suspension is formed. This is an emulsion.
When fats rubbed against paper, the paper became translucent. When the paper is dipped in ether, translucent disappears because the oil dissolves in ether.
In mixtures of lipid and water, the lipid separates and moves to the top. When shaken with Sudan III solution, this lipid absorbs the dye of Sudan III solution, turns red, and produces a "red ring" at the top of the test tube. Stained lipids globules will float on the top of water because they are less dense then water. This is the basis for testing lipids by using Sudan (III) solution.

Uses of lipids are as follows:-

They are source of energy. They can be broken down during respiration process to release energy.
Fat adipose tissues below the skin insulate the body against heat loss.
Lipids act as a source of metabolic water when fats and oils are oxidized. This is an alternative source of water for the animal living in desert area like camel.
Fats deposited around the major organs such as kidney, liver and heart protect those organs and they act as shock absorbers.
They form major structural component of the cell membrane. For example phospholipid is a special type of lipid which is a major component of cell membrane.
They are medium for storing fat soluble vitamins like vitamins A, D, E and K.

Biology practical food test form four

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