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Biology Practical O’level Food Tests

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Biology Practical O’level Food Tests

Food test: Are used to determine which nutrients are present in a food specimen.

At this level, we will learn how to test for carbohydrates, proteins, and lipids.

CARBOHYDRATES

Carbohydrates includes: starch, reducing sugar, and non-reducing sugar, that may contains glucose inside of them.

SOURCES OF CARBOHYDRATES

The following are some of the food that contains nutrients of carbohydrates:

Maize, Rice, Cassava, Potatoes, Bananas e.t.c

TYPES OF CARBOHYDRATES

There are three types of carbohydrates:

1. MONOSACCHARIDES

These are also known as simple sugar.

Example of monosaccharides are: Glucose, Fructose (fruit sugar), and Galactose (milk sugar).

Characteristics of monosaccharides

-They are sweet.

– They dissolve in water to form sweet solution.

– They are crystalline.

– They are all reducing sugar.

2. DISACCHARIDES

These are formed when two monosaccharides molecules combined.

Example of disaccharides are: maltose, lactose, and sucrose.

Characteristics of disaccharides

– They are sweet.

– They are crystalline.

– They dissolves in water to form sweet solution.

– Some are reducing sugar (maltose and lactose), and some are non-reducing sugar (sucrose).

3. POLYSACCHARIDES

Are formed by condensation involving several monosaccharides.

Example of polysaccharides are: starch, glycogen, chitin, and cellulose.

Characteristics of polysaccharides

– They are not sweet.

– They are insoluble in water.

– They are non-crystalline.

– They form suspensions with water.

– All are non reducing sugar

– Sources of Starch are: Cassava, potatoes, yams, cereals.etc

– Sources of Reducing sugar are: onion, carrot, sugar cane, germinating cereal grains.

– Sources of Non- reducing sugar are: sugar cane, fresh milk, beet root.etc

FUNCTIONS OF CARBOHYDRATES (starch, reducing, and non-reducing sugar)

– Used as a source of energy in the body.

– Regulation of blood glucose in the body.

– Dietary fiber.

– Biological recognition processes.

– Provides flavor and sweeteners. eg sucrose, fructose, and glucose.

– They form important component of cell membrane.

Hypoglycemia and Ketosis ; are diseases caused by lack or inadequate amount of carbohydrates in the body.

Carbohydrates are digested in the body inform of starch.

* Digestion of starch in the alimentary canal takes place at the mouth and duodenum.

* At the mouth, the enzyme involved in the digestion of starch is called salivary amylase (ptyalin).

* At the duodenum, the enzyme involved in the digestion of starch is called pancreatic amylase.

* The end- product of digestion of starch is Maltose.

PROTEINS

SOURCES OF PROTEINS

Egg, Irish potatoes, Beans, Meat, Milk, Fish e.t.c.

FUNCTIONS OF PROTEINS

– Used as a source of energy to the body.

– Used for tissue growth.

– Used for repair the damaged tissue.

– Used in the formation of some tissues. eg hair, nail e.t.c

– They form part of the cell structure.

:Lack of proteins in the body can cause disease called Kwashiorkor.

* The digestion of proteins in the alimentary canal takes place at the Stomach and duodenum.

* At the duodenum, the enzyme involved in the digestion of protein is called Trypsin.

* At the stomach, the enzyme involved in the digestion of protein is called Pepsin.

* The end- product of digestion of protein is Peptides.

LIPIDS

Lipids includes Fats and Oils.

SOURCES OF LIPIDS

.Groundnuts, Coconuts, Avocado, Milk, Meat e.t.c

FUNCTIONS OF LIPIDS

– Used as a sources of energy in the body.

– They protect internal organs like hear, kidney etc.

– Insulate the body against heat loss.

– They assist mechanism of buoyance in marine organisms.

– They are important component of cell membranes.

Excessive amount of lipids in the body can cause Obesity.

Lack of lipids in the body can cause the deficiency of vitamin: A, D, E, K etc

* The digestion of lipids in the alimentary canal takes place at the Duodenum.

* The enzyme involved in the digestion of lipids is called Pancreatic Lipase.

* The end- product of digestion of lipids is Fatty acids and Glycerol.

FOOD TEST EXPERIMENT

REAGENTS USED DURING FOOD TEST

Iodine solution,
Benedicts solution,
Hydrochloric acid (HCl),
Sudan III,
Sodium hydroxide (NaOH)/potassium hydroxide(KOH)/ Sodium hydrogen carbonate(NaHCO3),
Copper II sulphate.

*Starch can be tasted by using IODINE SOLUTION. If starch present , the colour will appear BLUE-BLACK.

* Reducing sugar can be tasted by using BENEDICT’S SOLUTION. If reducing sugar present, the colour will change from BLUE to GREEN to YELLOW to BRICK RED PRECIPITATE.

* Non- reducing sugar can be tested by using DILUTE HYDROCHLORIC ACID, SODIUM HYDROXIDE(NaOH)/ Potassium hydroxide(KOH)/ Sodium hydrogen carbonate(NaHCO3), and BENEDICTS SOLUTION. If non-reducing sugar present the colour will change from BLUE to GREEN to YELLOW to BRICK RED PRECIPITATES.

* Proteins can be tetsed by using SODIUM HYDROXIDE SOLUTION and COPPER II SULPHATE. If proteins present the colour will appear PURPLE.

*lipids can be tested by using SUDAN III. If lipids present, the RED DROPLETS will appear on the surface.

NOTE:

– The function of hydrochloric acid is to neutralizes disaccharides to monosaccharides.

– The function of Sodium hydrogen carbonate is to hydrolyzes the acid.

PRINCIPLES OF WRITTING FOOD TEST PRACTICAL REPORT

– It must have four parts: Food tested, Procedure, Observation, and Inference.

– Passive past tens must be used instead of present tens.

– If not guided, the food must be tested in a series of: Starch, Reducing sugar, Non- reducing sugar, Proteins, and the last is Lipids.

– Use specific amount of sample solution and reagents; eg 2mls or two drops and not few mls or few drops.

– It must have a heading at the top.

– If reducing sugar present, no need for testing non- reducing sugar.

Biology Practical O’level Food Tests

FOOD TEST PRACTICAL REPORT

NB:

Assume you are provided with solution Z.

S/NO.	TEST FOR	PROCEDURES	OBSERVATION	INFERENCE
1.	STARCH	2mls of solution Z was added in a test tube, then 2 drops of Iodine solution were added and shaken the mixture.	-Blue black colour was observed -Yellowish brown iodine was observed	-Starch was present. -Starch was absent.
2.	REDUCING SUGAR	2mls of solution Z was added in a test tube, then two mls of Benedicts solution was added and boiled for about 2 to 3 minutes.	-Colour changed from: blue to green to yellow to brick red precipitate. – Blue colour of Benedicts solution was retained.	-Reducing sugar was present. Reducing sugar was absent.
3.	NON-REDUCING SUGAR	2mls of solution Z was put in a test tube, then 1ml of dilute Hydrochloric acid was added and boiled for about 2 to 3 minutes then cooled. After cooled, 2mls of Sodium hydrogen carbonate was added followed by 2mls of Benedicts -solution and boiled for about 2 to 3 minutes.	– Colour changed from: blue to green to yellow to brick red precipitates. -Blue colour of Benedicts solution was retained.	– Non-reducing sugar was present. -Non-reducing sugar was absent.
4.	PROTEIN	2mls of solution Z was put in a test tube, then 1ml of sodium hydroxide solution was added and shaken followed by 2- drops of Copper two sulphate and shaken the mixture.	– Purple or violet colour was observed . Blue colour of Copper two sulphate was retained.	– Protein was present. -Protein was absent.
5.	LIPIDS	2mls of solution Z was put in a test tube,then 2-drops of Sudan three was added, shaken the mixture and allowed to settle. Few drops of solution Z was poured on a piece of paper.	– Red droplets was observed on the surface. Red colour of Sudan three was uniformly distributed throughout the solution. Translucent mark appeared on the paper.	– Lipids was present. Lipids was absent. -Lipids was present.