Determination of N/Protein in Cereals by Kjeldahl Method (CAT#: STEM-EA-0037-ZJF)

Introduction

Cereals contain between 8-15% of different kinds of proteins such as albumins, globulins, prolamines, gliadins, glutelins and glutenins. Their chemical composition is important not only for nutritional purpose, but also for the bread dough and its process of baking. Gliadins and glutenins, with water contact, form gluten, a lipoproteic substance that gives viscosity, elasticity and cohesion to dough, helping it to rise and to keep its shape; it is found in wheat and other grains, including barley and rye.
For legal purpose it’s important to know the proteins amount in cereal flours, because, generally, their commercial quality depends on it.
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 digestion temperatures higher than 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.