Determination of N/Protein in Soybean by Kjeldahl Method (CAT#: STEM-EA-0048-ZJF)

Introduction

Soybean meal is the most important protein source used to feed farm animals. Soybean meal is the by-product of the extraction of soybean oil. In the solvent extraction process, the soybeans are cracked, heated, flaked and the oil is extracted by solvent. The extracted flakes are then dried to eliminate the solvent, toasted and ground. The soybeans may have been de-hulled prior to extraction, and the hulls may be added back at the end of the process.<br />Thanks to the high level of precision and reproducibility and to its simple application, Kjeldahl is nowadays the most used method for determining nitrogen and protein contents in the food and feed industry. It also has several other applications in environmental control (phenols and nitrogen in water, sludge, soil and lubricants) and in the chemical and pharmaceutical industry according to official AOAC, EPA, DIN e ISO procedures. 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 temperature 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.