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TEST FOR FOOD SUBSTANCES

HOW TO TEST FOR FOOD SUBSTANCES The chart below represents the TEST FOR FOOD SUBSTANCES various classes of food substances such as starch, protein, simple sugars, reducing sugars, fats and oil and water. 

test for food substance

1. HOW TO TEST FOR PROTEINS IN FOOD

(a) The Biuret’s test.
Process
i. Take a small quantity of milk or egg white solution
ii. Add 1cm of protein and sodium hydroxide and 1% copper (11) solution in drops
iii. Shake the mixture after each drop.
iv. Do not heat

OBSERVATION TEST FOR FOOD SUBSTANCES
The mixture will turn purple or violet colour.
INFERENCE
Protein is present
(b) Millon’s test
i. Put 3cm of protein food inside a test tube, e.g. fresh egg white
ii. Add 3cm of Millon’s reagent
iii. Warm the mixture in a water bath for few minutes

OBSERVATION
A red precipitate would appear

INFERENCE

Protein is present

(c) XANTHOPROTEIC TEST FOR FOOD SUBSTANCE

i. Put 2cm of egg white or milk solution in a test tube
ii. Add about 1cm of concentrated trioxonitrate (v) acid and 3cm of ammonium hydroxide solution
iii. Heat the solution
iv. Allow it to cool down

OBSERVATION

A white precipitate forms, which turns yellow on heating. On cooling the content after adding excess NH4OH, the solution becomes orange in colour

INFERENCE
Protein is present

2. FOOD TEST FOR STARCH

I. collect any starch material like bread or yam
II. Add a few drops of dilute Iodine solution

OBSERVATION
I. The colour will change to blue-black
INFERENCE
Starch is present

3. FOOD TEST FOR SIMPLE SUGARS e.g. glucose and fructose

i. Put a small quantity of glucose solution in a test tube
ii. Add 2% Benedict solution
iii. Boil the mixture for 4-6 minutes

OBSERVATION

A brick-red or orange precipitate is seen

INFERENCE
Glucose is present

4. FOOD TEST FOR REDUCING SUGARS e.g. sucrose, lactose or maltose

i. Put a small quantity of sucrose solution in a test tube
ii. Add a few drops of Benedict’s solution or Fehling solution
iii. Add a few drops of Hel:
iv. Boil the mixture for a few minutes
Dilute Hcl and boiling will help to hydrolyze the sucrose to simple sugars e.g. glucose

OBSERVATION
A yellow precipitate is observed

INFERENCE TEST FOR FOOD SUBSTANCES
Sucrose or non-reducing sugars is present

 TEST FOR FATS AND OILS IN FOOD

(a) Translucent test
i. Drop oil on a spot on a filter paper
ii. Observe the spot against a source of light
OBSERVATION
The drop of oil becomes more translucent. Which means it allow more light to pass through it when held in front of it

INFERENCE
The translucency shows the presence of fats and oils

(b) SUDAN (iii) TEST

i. Add a few drops of Sudan (iii) solution to in a test tube
ii. Then boil the solution
OBSERVATION TEST FOR FOOD SUBSTANCES
i. A red colouration appears before boiling.
ii. A black precipitate is form on boiling

INFERENCE

Fats and oil is present

(6) TEST FOR WATER
i. Dip a blue, dry cobalt chloride paper in a food item
OBSERVATION
The colour of the paper changes from blue to pink

INFERENCE

Water is present

agricultural biology topics
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Agricultural biology topics

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    61. MAIZE SMUT
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    63. MAIZE RUST
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    66. COCOA BLACK POD DISEASE

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