How to analysis protein in Bakery and Confectionery Product? Calculation explanation for Kjeldahl Method?

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How to Analysis Protein in Bakery and Confectionery Products

 

This method is applicable for the determination of Protein in Bakery and confectionary products.

 Method

     Kjeldahl Method

 

Required Chemicals

     Sodium Sulphate or Potassium Sulphate

     Cupric Sulphate

     0.1 N Sulphuric Acid

         Mix 1.4 ml of concentrated sulphuric acid in 500 ml SMF and makeup with distilled water.

        Standardize the solution using 0.1N Sodium Hydroxide or Potassium Hydroxide.

 

    4% Boric Acid Solution

         Weigh 4 g of boric acid into a beaker and dissolve the salt using distilled water and makeup to 100 ml.

 Sodium Hydroxide – 40%

        Take 400g of Sodium Hydroxide in a 1L beaker. Mix with distilled water. Mix Carefully.

         Concentrated Sulphuric Acid

         Mixed Indicator

 

PROCEDURE

 Sample Preparation  

        A Well-mixed sample is used for the test. For Solid sample weigh 0.2 to 0.3 g of the test sample(eg., Bakery products, Mixture, etc.,), for semi-solid sample weigh 0.3 to 0.5 g of the test sample (eg., fruits, sauces).

           

Sample Analysis

 Bakery and confectionery products weigh approximately about 0.2 to 0.3 gm of sample into the analysis Kjeldahl Flask.

 Add 10g of Sodium sulphate or Potassium Sulphate and 0.2 to 0.3g of Cupric Sulphate in the Flask. Then add 20ml of Concentrated Sulphuric Acid to the flask.

Kjeldhal method Digestion Process

 Digest the Flask on Heating Mantle until the complete digestion is approximately 90 minutes (the clear green color appears).

 Simultaneously prepare a blank without sample.

 After digestion cools the Flask using an insert tube rack.

 Then Fix the tube into the distillation unit using 35 to 50 ml of 40 % sodium hydroxide solution.

Simultaneously take 25 ml of 4 % Boric acid with mixed indicator into a 250 ml conical flask and immerse the tip of the receiver into the conical flask

Kjeldhal Method Digestion and Distillation Process Setup

 The initial stage of boric acid and the mixed indicator shows the pink color. After the process of Distillation the pink color change into green color.

 After complete, the distillation process, titrate the collected boric acid (That green colour solution) using 0.1 N H₂SO₄ (End Point Green to Pink) & titrate the blank also.

 Calculate the Nitrogen value from the calculation and multiply the Nitrogen by 5.7 for calculating the protein

           

Calculation Formula:

 

            Nitrogen % = 14.01 x (ml titrant-ml blank) x N x 100

                                     Sample weight (gm) x 1000

           

            Protein    %= Nitrogen x 5.7

 

 

Calculation Example:

 

            Sample Weight                          = 0.2598g

 

            Blank Titration Value                  = 0.1ml

 

            Sample Titration Value               = 2.4ml

 

            Normality of Sulphuric Acid       = 0.1N

 

 

            Nitrogen(%)       = 14.01 x (2.4-0.1) x 0.1 x 100

                                                0.2598 x 1000

 

 

                                    = 322.23

                                        259.8

 

                                    = 1.24 %

 

            Protein (%)        = 1.24 x 5.7

 

                                    = 7.1%

 

Reference

      

FSSAI Manual Method for Beverages and Confectionery products

AOAC 20^thEdn Chapter 32, 923.04-2016 – Official methods of Analysis & Instrument Manual