Short Note #21: Protein Determination in Cheese According to the Kjeldahl Method

Buchi Kjeldahl Solutions - Food & Beverage

Buchi Kjeldahl Solutions - Food & Beverage

The determination of protein in food is a routine procedure for quality assurance and labeling and is one of the key analyses performed in the food industry. A simple and fast procedure for protein determination in cheese, as described in the DIN EN ISO 8968:2001 appendix A regulations, is introduced in this short note. Download the short note on the protein determination in cheese and review our Kjeldahl Applications database to request or download our other short notes.

Introduction:
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 sulphuric acid solution. The nitrogen content is multiplied by a sample-specific factor (6.38 for cheese) to obtain the protein content.

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

Samples:
Cream cheese and Emmentaler cheese, grinded, labeled protein contents 6 % and 33 %, respectively.

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