Short Note #34: Protein Determination in Nuts According to Kjeldahl

The determination of protein in food is a routine procedure and one of the key analyses performed in the food industry for quality assurance and labeling. A simple and fast procedure for protein determination in nuts, as described in the AOAC 950.48, is introduced in this study. Please contact Buchi to request this short note and find out about our other Kjeldahl applications.

The samples require digestion with sulfuric acid to convert nitrogen into ammonium sulfate. After conversion to ammonia through the alkalinization with sodium hydroxide, the sample is distilled into a boric acid receiver by steam distillation, followed by a titration with sulfuric acid solution. The nitrogen content is multiplied by a sample-specific factor (5.18 for almonds and 5.30 for
other tree nuts) to obtain the protein content.

The sample is digested with sulfuric acid using the SpeedDigester K-436 or K-439, followed by distillation and titration with the KjelFlex K-360. The determined protein contents correspond to the labeled values.

Instrumentation: SpeedDigester K-436, K-439 (See Below Product Facts), KjelFlex K-360

Almonds and hazelnuts, labelled protein contents 22% and 14%, respectively.

SpeedDigester K-439 - Kjeldahl Digestion

SpeedDigester K-439 - Kjeldahl Digestion