Skip to content
Home » Estimation of Lactose in Milk by Titration Method

Estimation of Lactose in Milk by Titration Method

Estimation of lactose in milk by titration method post we briefly summarise about: principle, reagents requirements, estimation of lactose in milk procedure, result, application and limitations of estimation of lactose in milk.

Estimation of Lactose in Milk by Titration Method

Fehling’s test for reducing sugars has been used since the 1800’s to determine the amount of glucose and other reducing sugars (lactose in milk, for example). It has had many applications including use in agriculture (glucose determination in corn for use in corn syrup) and in edicine (glucose determination in urine for diabetes tests).

Principle

Lactose is reduce in disaccharide when it is treated with visibility reagent like Fehling’s reagent. The cupric ion present in the reagent and converted into cuprous ions by reducing the activity of lactose. This property is mainly used in estimation of lactose in milk.

Requirements

Materials

1. Burette

2. Burner

3. Conical Flask

4. Stand

5. Water Bath

Chemicals

1. Cuprous sulphate

2. Sodium potassium hydroxide

3. Sodium hydride

4. Potassium tartarate

5. Methylene blue

6. Lactose

Reagents

1. Fehling’s solution A: Dissolve 34.64 gm of pure cuprous sulphate crystals in distilled water in a 500ml measuring flask and made up to 500ml.

2. Fehling’s solution B: Dissolve 173gm roucheller (sodium potassium hydroxide). In distilled water and dissolved 5gm at pure sodium hydride in 5ml of distilled water and added to the former potassium tartarate and made the solution to 500ml with distilled water.

3. Methylene blue indicator: Dissolve 1gm of methylene blue powder and made up to 100ml in total volume.

4. Lactose solution: Small amount of lactose was taken and dried in a vacuum desiccator over concentrated sulphuric acid for six hours. Dissolve 5gm of dried lactose crystal in 100ml with distilled water and boiled, cooled in dissolved water.

Procedure

1. 10ml of Fehling’s solution A and B are pipetted separately into 250ml conical flask with 25ml of lactose was added into a flask containing Fehling’s solution and mixed and boiled gently for 2 minutes. Added 2-3 drops of methylene blue indicator while boiling.

2. The addition of lactose was continued with 2 drops at 10 seconds by holding the burette in hands stop for the further addition of lactose as soon as the blue colour of the methylene blue is disappeared. 

3. The titration should be heated with 10 ml portion of Fehling’s solution. Thus the value of lactose is determined. Estimation of lactose in milk percentage estimated as follows. 10 ml of milk is estimated as measuring flask and made up to 100 ml by adding distilled water. 

4. 25 ml of dilute milk was taken in conical flask containing 10 ml of Fehling’s solution A and B. Boil for 2 minute and added 3-5 drops of lactose solution at a time intervals of 10 seconds until the end point reached. 

5. The titration is repeated two or more proportion of 25ml distilled milk to determine the exact quantity of lactose. Assuming that Fehling’s solution along required with 25ml of dilute milk. Since 1ml of lactose solution contain 0.005gm of lactose and the amount of lactose present in 25ml of dilute milk is obtained.

Calculation

The amount of lactose present in 100ml of undiluted milk is _______________.

Further Readings

Reference