Milk protein content estimation

Estimation of Protein content of Milk by Formol Titration Method

Author : Nadim Dinani

Is the milk you drink rich in proteins? Is the source of milk labelled on your milk carton true? many more questions and here is an answer.

Milk is the well known single food highly rich in protein content. Besides protein it contains fats, carbohydrates, inorganic salts and vitamins. Casein is the most prominent protein constituting 80% of all the milk proteins. Among the other proteins are beta-lactoglobulin, lactalbumin, and alpha-albumin.

Although proteins are too weak to be titrated with alkali, if formalin i.e. formaldehyde gas dissolved in water, is added to neutral milk, it reacts with the amino group of amino acids present to form dimethylamino acid derivatives. Consequently the amino acids release H⁺ ion i.e. free acid. Also the carboxyl group is available for titration. The amount of acidity developed is directly proportional to the concentration of protein. The amount of acid released is estimated by titrating it against NaOH using phenolphthalein as an indicator. The colour change is from colourless to faint pink.

Calcium which is found in milk in high concentration interferes with the titration. Hence it is removed by adding saturated potassium oxalate to milk prior to the titration. This sample is neutralized with NaOH to pH 7. This volume of NaOH will not be included in the titration reading.

A blank titration using distilled water is also carried out in the same manner. Distilled water does not require Calcium elimination and thus the step can be skipped.

Protein content of milk in Gram % will be 1.7 x (Test titration reading – Blank titration reading)

Using this, source of milk can be derived. Standard values of Buffaloes’ milk, cow’s milk, and goat’s milk are 3.9, 3.4 and 3.5 respectively.