Short Note #47: Protein Determination in Eggs According to Kjeldahl

Protein Determination in Eggs

Protein Determination in Eggs Using Kjeldahl

A simple and fast procedure for protein determination in eggs, as described in the AOAC 925.31 and LFGB § 64 L05.00-15, is introduced within this Short Note #47.

The sample is digested with sulfuric acid using the SpeedDigester K-436 or K-439, followed by distillation and titration with the Kjeldahl Sampler System K-370/K-371. The determined protein contents correspond to the values from literature (see Short Note #47 for details).

Protein determination is one of the key analyses performed in the food industry. The samples require digestion with sulfuric acid to convert nitrogen into ammonium sulfate. After conversion to ammonia through the alkalization with sodium hydroxide, the ammonia is distilled into a boric acid solution by steam distillation, followed by a titration with sulfuric acid solution. The nitrogen content is multiplied by a sample specific factor (6.25 for egg) to obtain the protein content.

Instrumentation: SpeedDigester K-436, K-439, Kjeldahl Sampler System K-370/K-371

Samples: Whole chicken egg, protein content 12.5 g/100g

Determination: Approx. 1.2 g of the homogenized sample were weighed in directly into a sample tube. A portion of 20 ml of sulfuric acid and 2 Kjeldahl tablets were added, and the digestion was performed using the “egg” method (K-439) or the parameters specified. After digestion the ammonia of the sample was distilled into a boric acid solution by steam distillation and titrated with sulfuric acid (See Short Note #47 for details).

The method was verified by using 0.13 g glycine as the reference substance.