Metrolab Blog

N/Protein Determination in Cheese according to the Kjeldahl method

Milk and dairy products play a role of primary importance in the human food, and are essential to the balance and the adequacy of the food ration. It is possible finding on the market, different kind of dairy products of different animal species, like sheep whole milk, goat whole milk and cheese, dried milk products including milk-based infant formulae. Commonly, it can be processed for the production of butter and cheese, such as the Greek “Feta” and the Italian “Caprino cheese”. Recently, this dairy product market has grown rapidly, because, for example, goat milk is very appreciated by lactose-intolerant people, due to low lactose content.
In order to create typical sensory features of these dairy products, it is important to know the attitude of the raw milk, depending also on its protein content. Due to the greater demand and consumption of goat/sheep dairy products, protein analysis has become more and more important to ensure food safety, food quality and fairness in international trade.

Protein Determination in Goat Cheese according to the Kjeldahl Method
Kjeldahl is nowadays the most used method for determining nitrogen and protein contents in foods and feeds, thanks to the high level of precision and reproducibility and to its simple application.
The modern Kjeldahl method consists in a procedure of catalytically supported mineralization of organic material in a boiling mixture of sulfuric acid and sulfate salt at with digestion block temperature at 400 °C. During the process the organically bonded nitrogen is converted into ammonium sulfate. Alkalizing the digested solution liberates ammonia which is quantitatively steam distilled and determined by titration.

Download the application note here.