According to James (1995), approximately 0.8-1.2 g of food was accurately weighed and transferred to a digestion tube. Two Kjeldahl tablets and concentrated sulphuric acid from an automatic dispenser were added. The tube was placed in the preheated digester at 420 0C for about 30 minutes until a clear solution is obtained.
After digestion, the tubes were removed from the digester, cooled and diluted with water. The tube with the digested and diluted sample was placed in the distillation unit. A conical flask containing 25 ml of boric acid (containing indicator) was placed under the condenser outlet. The alkali (25 ml of 40% NaOH) was dispensed and distilled for 4 minutes. The ammonium borate solution formed was titrated with 0.1M sulphuric acid to a purplish-grey end-point.
Using 0.1M sulphuric acid for titration
% Nitrogen content = 0.14 x A divided by
weight of food in grams
Where A = volume (ml) of 0.1M sulphuric acid used in the titration.
% Protein = % Nitrogen x 100 divided by
% Nitrogen in protein
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