How to Analyse Protein in Liquid Samples (Formol Titration Method) - BIOSCIENCE EDUCATION

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Monday 11 January 2021

How to Analyse Protein in Liquid Samples (Formol Titration Method)

 How to Analyse Protein in Liquid Samples (Formol Titration Method)

AIM: To determine the amount of protein in a liquid sample. 

APPARATUS: Conical flask, Burette, Retort stand, Clamp,  

REAGENT: 1% Phenolphthalein, 0.1M NaOH, Formaldehyde. 

PRINCIPLE: When formaldehyde (Methanal) is added to a previously neutralised food, the formaldehyde reacts with the side chains of basic amino acid residues such as lysine. This results in the conversion of –NH groups to 2-N=CH groups which leads to loss of basic properties and an increase in the acidity of the protein. The increase in acidity is then measured by titration with sodium hydroxide using phenolphthalein as indicator and the increase in acidity is correlated with protein concentration from previous calibrations or a known conversion factor.


1) Measure 10ml of the sample into a conical flask 2) Add 2-3 drops of 1% Phenolphthalein 3) Titrate against 0.1M NaOH in the burette till a pink colouration is observed, add 2ml of formaldehyde to return to original colour and continue the titration till colour change is obtained again, then add another 2ml of formaldehyde again till a pink colouration appear. 4) Record your titre value and calculate. 


% Protein (MSNF) = Titre value *5.67% 

%protein = T x 0.17 

Where T= ml M NaOH required to neutarlise the acidity produced in 1000 ml milk. 

It may also be used for estimating the non-fat milk solids present in ice cream 

MSNF= Milk Solid Non Fat

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